Wellness Goals · Sleep habits
Caffeine, Alcohol, Nicotine and Sleep
Caffeine, alcohol and nicotine (substances that affect sleep) · also called Caffeine and sleep, alcohol and sleep, smoking and sleep, nicotine and sleep, coffee before bed, nightcap, cafeína alcohol y sueño
Caffeine and nicotine are stimulants, and alcohol is a depressant that can feel sedating at first. All three can change how fast you fall asleep, how deep your sleep is and how often you wake. This page covers how caffeine, alcohol and nicotine affect sleep: timing advice from the NHS and NHLBI, home and lab trials of late caffeine, alcohol and sleep apnea, quitting smoking, and safety notes. Evidence is strongest for caffeine timing and alcohol and REM sleep, and weaker for nicotine and vaping.
General information, not medical advice. Last substantive update · Not medically reviewed. A named clinician has not signed off on this page. How this page is made
About Caffeine, Alcohol, Nicotine and Sleep
Caffeine and nicotine are stimulants and can delay and fragment sleep, and alcohol may help you drop off but lightens and breaks up the rest of the night. A 2023 meta-analysis of 24 studies found caffeine cut sleep by about 45 minutes; a 2025 meta-analysis found even two drinks reduce REM sleep. The NHS advises no smoking, alcohol, tea or coffee for at least 6 hours before bed. See a doctor if poor sleep lasts months or if you snore loudly or stop breathing in your sleep.
How caffeine, alcohol and nicotine affect sleep: the short version
Caffeine and nicotine are stimulants. Alcohol is a depressant that can make you drowsy at first. All three can change how long it takes to fall asleep, how deep sleep is and how often you wake.
Responses differ a lot between people, and trials are often small, so the numbers here describe groups, not you.
Caffeine and sleep: timing, amounts and hidden sources
The FDA lists typical amounts per 12 fl oz: caffeinated soft drinks 23 to 83 mg, green tea 37 mg, black tea 71 mg, brewed coffee 113 to 247 mg and energy drinks 41 to 246 mg. Decaf typically still has 2 to 15 mg per 8 fl oz cup. For most adults the FDA cites 400 mg a day as not generally linked with negative effects, while sensitivity varies widely.
In a 2013 home trial a 400 mg dose disrupted sleep even 6 hours before bed. A 2025 crossover trial found 100 mg had no significant effect while 400 mg did, and the effect grew the closer to bedtime. A 2023 meta-analysis of 24 studies estimated a coffee should be taken at least 8.8 hours before bed to avoid losing sleep time. These are study results, not a personal limit.
Alcohol and sleep: why a nightcap can backfire
The NHLBI says alcohol can make it easier to fall asleep but can lead to lighter sleep and more waking. A 2025 meta-analysis of 27 studies found REM sleep was delayed and reduced even after about two standard drinks, worse with higher doses.
Meta-analyses link alcohol with more breathing pauses and lower oxygen levels in sleep, most in people who snore or have sleep apnea. If you drink heavily, speak to a doctor before stopping suddenly.
Nicotine, smoking, vaping and sleep
A review of 52 studies found nicotine use is linked with longer time to fall asleep, fragmented sleep and less deep and REM sleep. The NHS lists smoking among things to avoid for 6 hours before bed and nicotine among causes of insomnia.
Sleep stays disturbed for the first few weeks after quitting and predicts relapse in the studies reviewed. E-cigarette users had higher odds of short sleep in cross-sectional studies, which cannot show cause.
Who is most affected: teens, pregnancy, snorers, and people with insomnia
The FDA says medical experts advise against energy drinks for children and teens. The NHS advises up to 200 mg of caffeine a day in pregnancy and says it is safest to avoid alcohol. People who snore or have sleep apnea are more affected by evening alcohol.
For people with insomnia, guidelines list CBT-I first; see our Insomnia page.
At a glance
Traditional uses history, not proof
Studied for research
- Stopping caffeine hours before bed, moderate certainty
- Avoiding alcohol before bed, moderate certainty
- Limiting alcohol with snoring or sleep apnea, moderate certainty
- CBT-I when insomnia and heavy drinking go together, moderate certainty
- Smaller caffeine doses, low certainty
- Stopping smoking and sleep, low certainty
- Teen caffeine and energy drinks, very low certainty
- E-cigarettes and sleep, very low certainty
Main compounds
- Caffeine
- Alcohol (ethanol)
- Nicotine
Common forms
- Coffee, tea, energy drinks and pre-workout products
- Alcoholic drinks
- Cigarettes, e-cigarettes and nicotine replacement
Research links: Caffeine and subsequent sleep, meta-analysis, 2023 · Caffeine taken 0, 3 or 6 hours before bed, 2013 · Alcohol and subsequent sleep, meta-analysis, 2025 · Alcohol and breathing in sleep, meta-analysis, 2018 · NHS: Insomnia · FDA: How much caffeine is too much · Research Library · Genes & Biomarkers Library
What it is and its history
- Accepted scientific name
- Caffeine, alcohol and nicotine as sleep disruptors
- Common names
- Caffeine, alcohol, nicotine and sleep (English); Cafeína, alcohol, nicotina y sueño (Spanish); Stimulants and sleep (English); Sueño y café, alcohol y tabaco (Spanish)
- Family or group
- Substances that affect sleep: a stimulant (caffeine), a sedative-like depressant (alcohol) and a stimulant (nicotine).
- Look-alikes and adulterants
- Name: Insomnia; Note: A sleep disorder that these substances can contribute to; see its own page.; Name: Sleep apnea; Note: Breathing pauses at night that alcohol and smoking can worsen.
What is inside, and how it may work
What it contains and how those compounds act in cells and animals. Laboratory and animal mechanisms are not proven effects in people.
Main compounds
| Compound | Family | Where it is concentrated | Activity studied | Level of evidence |
|---|---|---|---|---|
| Caffeine | methylxanthine stimulant | FDA per 12 fl oz: soft drinks 23 to 83 mg, green tea 37 mg, black tea 71 mg, brewed coffee 113 to 247 mg, energy drinks 41 to 246 mg. | Stimulant; the 2024 review says it blocks adenosine receptors. 23 5 | Human data |
| Alcohol (ethanol) | depressant | May shorten time to fall asleep at high doses; reduces REM sleep and worsens breathing in sleep. 7 13 | Human data | |
| Nicotine | stimulant alkaloid | Linked with longer time to fall asleep, fragmented sleep and less deep and REM sleep. 8 | Human data |
Mechanisms, receptors and pathways
| Target or pathway | Gene or receptor | What was found | Level |
|---|---|---|---|
| Why caffeine disturbs sleep | The 2024 narrative review says caffeine blocks adenosine receptors. This is a proposed pathway and was not tested in the trials read. 1 | Proposed |
Isolated compounds versus whole extracts
The trials used caffeine capsules or coffee; real drinks contain other compounds and different amounts. Tea, chocolate and energy drinks differ in caffeine content.
4 moderate certainty2 mixed findings4 low certainty3 very low certainty
What was looked at
The 13 benefits and uses checked for Caffeine, Alcohol, Nicotine and Sleep, each with how strong the evidence is. Tap one to open it.
- Stopping caffeine hours before bedModerate certainty
- A smaller caffeine doseLow certainty
- Knowing your own caffeine sensitivityLow certainty
- Regular bedtime caffeine and partial toleranceLow certainty
- Evening caffeine before trainingMixed findings
- Reducing caffeine and energy drinks in teenagersVery low certainty
- Avoiding or limiting alcohol before bedModerate certainty
- Limiting alcohol if you snore or have sleep apneaModerate certainty
- Do alcohol and smoking cause insomnia? Genetic evidenceMixed findings
- CBT-I when insomnia and heavy drinking go togetherModerate certainty
- Stopping smoking and sleepLow certainty
- A behavioural sleep program for smokers with insomniaVery low certainty
- Electronic cigarettes and sleepVery low certainty
Lab markers tracked in the studies
Total sleep timeTime to fall asleep (sleep onset latency)Breathing pauses per hour (apnea-hypopnea index, AHI)REM (dream) sleep
What is Caffeine, Alcohol, Nicotine and Sleep good for?
These are the habits and approaches studied for caffeine, alcohol and nicotine in relation to sleep, and how strong the human evidence is for each. They describe what studies found, not advice to change anything. Established medical care is described in the About tab.
Benefits, one by one
Each card is a research question, not a promise. Tap a goal to filter. Open a card to see the studies, doses and limits.
Stopping caffeine hours before bed
Moderate certaintyA 2023 meta-analysis of 24 studies found caffeine cut total sleep time by about 45 minutes and sleep efficiency by 7 percent. A home trial found 400 mg disrupted sleep even when taken 6 hours before bed, and a later crossover trial found the disruption grew the closer the dose was to bedtime. The NHS advises no tea or coffee for at least 6 hours before bed.
5 studiesDoses in the trials were 100 mg to 400 mg given once; the meta-analys…
Studies, doses and limits
What the trials found
Meta-analysis of 24 studies (Gardiner 2023); a home randomised crossover trial in adults (Drake 2013; sample size not in the abstract); a randomised crossover trial in 23 men (Gardiner 2025).
Results
Pooled: total sleep time -45 min, sleep efficiency -7%, time to fall asleep +9 min, time awake after sleep onset +12 min, light sleep (N1) +6.1 min, deep sleep (N3 and N4) -11.4 min. The authors estimate a coffee (107 mg per 250 mL) should be taken at least 8.8 hours before bed to avoid losing total sleep time. Drake 2013: 400 mg at bedtime, 3 hours or 6 hours before bed each disturbed sleep versus placebo. Gardiner 2025: 400 mg within 12 hours of bed delayed sleep and changed sleep stages; more fragmentation within 8 hours.
Effect sizes as reported
Total sleep time -45 min; sleep efficiency -7%; sleep onset +9 min; wake after sleep onset +12 min (confidence intervals not in the abstract)
Why this rating
Moderate, the compiler's rating: a meta-analysis of 24 studies and two randomised, placebo-controlled crossover trials point the same way, but the trials were small, mostly in young, healthy people, and often used large single doses (400 mg).
Form and dose studied
Doses in the trials were 100 mg to 400 mg given once; the meta-analysis pooled many doses. These are amounts studied, not advice.
Who was studied
Healthy adults, mostly young; 23 men in the 2025 trial.
Limits
Small trials, mostly healthy young people with moderate habitual intake; 400 mg is a large single dose; older adults, women and people with insomnia are under-represented in the abstracts read.
Why researchers looked
Caffeine is a stimulant, and researchers wanted to know how long before bed it still matters.
Proposed mechanism Hypothesis
Proposed in the 2024 review: caffeine blocks adenosine receptors, which slows sleep onset and lightens sleep. Not tested directly in the studies read.
A proposed mechanism does not show that the effect happens in people.
Caffeine can raise heart rate and cause jitters and anxiety. The FDA lists insomnia among the signs of too much caffeine.
A smaller caffeine dose
Low certaintyIn a randomised crossover trial of 23 men, a 100 mg dose of caffeine had no significant effect on sleep even when taken 4 hours before bed, while 400 mg did. In 18 teenage boys, 80 mg taken 4 hours before bed did not strongly cut deep sleep or sleep quality on average, but some teens lost deep sleep.
3 studies100 mg and 400 mg once (adults); 80 mg once (teens). Amounts as repor…
Studies, doses and limits
What the trials found
Randomised crossover trials: 23 men aged 25 on average (Gardiner 2025) and 18 male teenagers aged 14 to 17 after a week of caffeine abstinence (Reichert 2020).
Results
100 mg: no significant effect on objective or subjective sleep versus placebo. 400 mg: significant effects. Teens (80 mg): subjective sleepiness fell; no strong group effect on deep sleep, but large differences between teens, and the ones with more deep sleep on placebo tended to lose some on caffeine.
Effect sizes as reported
Not given as numbers in the abstracts for the 100 mg result.
Why this rating
Low, the compiler's rating: two small trials, one in men only, one in boys only, with high person-to-person variation.
Form and dose studied
100 mg and 400 mg once (adults); 80 mg once (teens). Amounts as reported, not advice.
Who was studied
Healthy young men and teenage boys.
Limits
Male-only samples; single doses; people with insomnia not studied; the adult trial found people had trouble judging how caffeine had affected their own sleep.
Why researchers looked
Dose matters: many people have a morning coffee but not several, so researchers compared smaller and larger doses.
Proposed mechanism Hypothesis
Not studied. The reviews propose that sensitivity and body size change the effect.
A proposed mechanism does not show that the effect happens in people.
Teens and children are more at risk from large amounts: the FDA says too much caffeine can cause fast heart rate, high blood pressure, anxiety and sleep problems in children and teens.
Knowing your own caffeine sensitivity
Low certaintyA 2023 review of 22 reports found that variation in the ADORA2A gene was linked with anxiety and sleep problems after caffeine, and variation in CYP1A2 with thinking tasks. This may explain why some people sleep fine after an espresso and others do not, but gene testing is not a proven way to pick a cut-off time.
2 studiesGenetic testing is not part of any guideline read here. Keeping a sim…
Studies, doses and limits
What the trials found
Systematic review of 22 reports (15 randomised trials, 6 cross-sectional studies, 1 genome-wide study) in healthy adults (Kapellou 2023).
Results
ADORA2A variants were associated with anxiety and sleep disturbance; CYP1A2 variants with cognitive function. Six reports covered sleep disturbance or insomnia.
Effect sizes as reported
Not given in the abstract.
Why this rating
Low, the compiler's rating: associations from mixed study types; the review calls for more work on which variants matter.
Form and dose studied
Genetic testing is not part of any guideline read here. Keeping a simple sleep diary is one way to see your own pattern (suggested by the NHS and by a 2024 narrative review).
Who was studied
Healthy adults.
Limits
Mixed designs, abstract only, not tested as a guide to personal advice.
Why researchers looked
People differ a lot in how caffeine affects them, and researchers looked for reasons.
Proposed mechanism Hypothesis
Proposed: gene differences change how fast caffeine is cleared (CYP1A2) and how strongly it acts on the brain (ADORA2A). Partly supported by the associations found; not tested as a way to guide advice.
A proposed mechanism does not show that the effect happens in people.
Do not rely on a gene result to judge caffeine safety.
Regular bedtime caffeine and partial tolerance
Low certaintyIn 19 good sleepers given 250 mg at bedtime for five days, most of the sleep disruption showed up on the first night, and only lower sleep efficiency lasted the week. Partial tolerance seemed to develop. That is not a reason to take caffeine near bedtime: sleep was still worse than on placebo.
1 studies250 mg at bedtime for five days, as reported.
Studies, doses and limits
What the trials found
Randomised, placebo-controlled, double-blind 2-week crossover trial in 19 good sleepers with low daily intake (0 to 141 mg) (Keenan 2014).
Results
On the first day: lower sleep efficiency, more fragmented sleep, poorer rated sleep quality, more early waking. Over the week only the lower sleep efficiency remained. Next-day effects on mood and performance appeared all week; working memory was better after caffeine, which the authors think was prevention of overnight withdrawal rather than a net benefit.
Effect sizes as reported
Not given as numbers in the abstract.
Why this rating
Low, the compiler's rating: one small trial in good sleepers with low usual intake, which may not apply to heavy users or people with insomnia.
Form and dose studied
250 mg at bedtime for five days, as reported.
Who was studied
Good sleepers with low habitual intake.
Limits
19 people; short; no people with insomnia.
Why researchers looked
Daily caffeine users wonder whether the body adapts.
Proposed mechanism Hypothesis
Proposed: the body adapts to repeated caffeine. Not tested directly.
A proposed mechanism does not show that the effect happens in people.
A habit of late caffeine can be hard to see because of withdrawal tiredness the next day; see a doctor if tiredness is heavy.
Evening caffeine before training
Mixed findingsA 2025 review of 10 studies of 128 athletes found a small drop in sleep efficiency (about 5 percent) after evening caffeine in randomised trials, but the result was not robust and total sleep time change was not significant. Athletes felt their sleep was clearly worse even when the measurements did not always show it.
1 studies3 to 6 mg per kg of body weight, as reported in the trials.
Studies, doses and limits
What the trials found
Systematic review with meta-analysis of 10 studies, 128 athletes (Kocak 2025).
Results
Sleep efficiency mean difference -4.87% (CI -7.45 to -2.29), not robust in leave-one-out checks; total sleep time -32.47 min (CI -69.93 to 4.99), not significant. Doses were 3 to 6 mg per kg body weight.
Effect sizes as reported
Sleep efficiency -4.87%
Why this rating
Mixed: objective changes were small and fragile, but athletes consistently reported worse sleep.
Form and dose studied
3 to 6 mg per kg of body weight, as reported in the trials.
Who was studied
Mostly male athletes.
Limits
Few studies, mostly men, mixed designs.
Why researchers looked
Athletes often use caffeine before late training or matches.
Proposed mechanism Hypothesis
Not tested.
A proposed mechanism does not show that the effect happens in people.
Large doses by body weight can cause jitters and fast heartbeat.
Reducing caffeine and energy drinks in teenagers
Very low certaintyIn a 2024 meta-analysis of studies of adolescents, higher caffeine intake went with higher odds of sleep problems (odds ratio 1.67). A UK-commissioned overview found that frequent energy drink use (5 or more days a week) went with sleep problems, headaches and other problems, but the evidence is weak and cannot show cause. No trial of cutting down was read.
3 studiesSurvey data on intake; no amounts are advised here.
Studies, doses and limits
What the trials found
Systematic review of 33 publications with a meta-analysis of 6 studies in ages 12 to 18 (Zhong 2024); overview of 15 systematic reviews plus UK surveys (Khouja 2022).
Results
Caffeine: odds of sleep problems OR 1.67 (CI 1.28 to 2.17). Energy drinks: linked with headaches, sleep problems, irritability, alcohol use and smoking; 13% to 67% of children had drunk them in the past year.
Effect sizes as reported
OR 1.67 for sleep problems with higher caffeine intake
Why this rating
Very low, the compiler's rating: mostly cross-sectional surveys, high differences between studies, GRADE weak, and the authors say intervention studies are needed.
Form and dose studied
Survey data on intake; no amounts are advised here.
Who was studied
Adolescents aged 12 to 18 and children under 18.
Limits
Cross-sectional data cannot separate cause and effect; sleepy teens may use more caffeine.
Why researchers looked
Teens are often short of sleep and many use caffeine or energy drinks to cope.
Proposed mechanism Hypothesis
Not tested.
A proposed mechanism does not show that the effect happens in people.
The FDA says medical experts advise against energy drinks for children and teens.
Avoiding or limiting alcohol before bed
Moderate certaintyA 2025 meta-analysis of 27 studies in healthy adults found that even about two standard drinks delayed and shortened REM (dream) sleep, and the effect grew with the dose. Only large doses (about five drinks) shortened the time to fall asleep, and that likely worsened REM sleep later. A large community survey linked heavier drinking with short sleep and snoring. The NHS and NHLBI both advise avoiding alcohol close to bedtime.
4 studiesAlcohol doses are given in grams per kg of body weight in the review;…
Studies, doses and limits
What the trials found
Systematic review and meta-analysis of 27 studies in healthy adults (Gardiner 2025); cross-sectional study of 11,905 adults in China (Zheng 2021).
Results
REM sleep onset delayed and REM duration reduced after low doses (0.50 g per kg or less, about two standard drinks), worse with higher doses. Shorter time to fall asleep only at 0.85 g per kg or more (about five drinks). Effects on total sleep time, efficiency and waking after sleep onset were too uncertain to call. Community study: heavy versus non-drinkers had higher odds of short sleep (OR 1.31) and snoring (OR 1.38).
Effect sizes as reported
Short sleep OR 1.31 (CI 1.09 to 1.57); snoring OR 1.38 (CI 1.22 to 1.57) for heavy versus non-drinkers
Why this rating
Moderate, the compiler's rating: a meta-analysis of 27 studies shows a consistent REM effect, but many studies were small and lab-based, and the survey cannot show cause.
Form and dose studied
Alcohol doses are given in grams per kg of body weight in the review; no amounts are advised here.
Who was studied
Healthy adults; adults in one Chinese community (hard liquor, not beer or wine, was linked to poor sleep quality).
Limits
Small short studies, uncertain effect on total sleep time; the survey was cross-sectional.
Why researchers looked
Many people use a drink to relax before bed, so researchers tested what it does to the night's sleep.
Proposed mechanism Hypothesis
Alcohol changes the balance of sleep stages; the review notes a delay and loss of REM sleep. The reason is not tested in the abstract.
A proposed mechanism does not show that the effect happens in people.
Alcohol is not a safe sleep aid; heavy drinkers who stop suddenly can have withdrawal, which can be serious, so they should get medical advice first.
Limiting alcohol if you snore or have sleep apnea
Moderate certaintyA 2018 meta-analysis of 14 trials (422 people) found breathing pauses per hour rose after alcohol, more in snorers and much more in people with sleep apnea. A 2020 analysis of lab data (279 people) and a 2018 analysis of 21 observational studies point the same way. The NHS advises not drinking too much alcohol, especially just before sleep, with sleep apnoea.
4 studiesSingle doses of alcohol in trials; amounts as reported, not advice.
Studies, doses and limits
What the trials found
Meta-analysis of 14 trials, 422 people (Kolla 2018); meta-analysis of 13 studies with sleep-lab data, 279 people (Burgos-Sanchez 2020); meta-analysis of 21 observational studies (Simou 2018).
Results
Apnea-hypopnea index +2.33 events per hour overall, +4.20 in snorers and +7.10 in people with sleep apnea; mean oxygen saturation -0.60%. Lab data: +3.98 events per hour and lowest oxygen -2.72%. Observational: higher alcohol use linked with 25% higher risk of sleep apnoea (RR 1.25), with publication bias.
Effect sizes as reported
AHI +2.33 (CI 1.41 to 3.25); RR 1.25 (CI 1.13 to 1.38)
Why this rating
Moderate, the compiler's rating: randomised-trial data and observational data agree, but studies were small, mostly male, and results varied (I2 up to 82 percent) with publication bias in one analysis.
Form and dose studied
Single doses of alcohol in trials; amounts as reported, not advice.
Who was studied
Adults who snore or have sleep apnea, and general adults (71.9% male in the trials).
Limits
Small studies, mostly men, heterogeneity, observational designs for the risk estimate.
Why researchers looked
Alcohol relaxes throat muscles, and researchers asked whether it worsens breathing in sleep.
Proposed mechanism Hypothesis
Proposed in the 2018 review: alcohol is a muscle relaxant that can worsen airway collapse. Not tested directly.
A proposed mechanism does not show that the effect happens in people.
Loud snoring, gasping or breathing pauses should be checked by a doctor; alcohol can mask or worsen them.
Do alcohol and smoking cause insomnia? Genetic evidence
Mixed findingsA genetic (Mendelian randomisation) study found strong evidence that insomnia raises the chance of alcohol dependence, smoking and cannabis use, that smoking initiation raises insomnia risk, and no evidence that alcohol per week or alcohol dependence causes insomnia. This does not match what sleep labs show about alcohol and night-time sleep, so the picture is mixed.
1 studiesNot a dosing study.
Studies, doses and limits
What the trials found
Two-direction Mendelian randomisation study using genome-wide data (Pasman 2020).
Results
Insomnia liability increased smoking traits, alcohol dependence and cannabis initiation; smoking initiation increased insomnia risk; no causal effect of drinks per week, alcohol dependence or cannabis on insomnia. Smoking heaviness and cessation could not be tested as exposures.
Effect sizes as reported
Not given in the abstract
Why this rating
Mixed: strong signals in one direction, but genetics measure long-term liability, not a single night of drinking.
Form and dose studied
Not a dosing study.
Who was studied
Large genetic cohorts; the abstract does not give the ancestry.
Limits
Cannot speak to one evening's drinks; ancestry and cohorts not given in the abstract.
Why researchers looked
Observational links between substances and insomnia could run either way, so researchers used genetics to test cause.
Proposed mechanism Hypothesis
Method: genetic variants act like a natural experiment. Findings depend on the method's assumptions.
A proposed mechanism does not show that the effect happens in people.
Poor sleep and substance use can feed each other; talk to a clinician if you rely on alcohol or nicotine to cope with sleep.
CBT-I when insomnia and heavy drinking go together
Moderate certaintyA 2025 meta-analysis of 8 randomised trials (426 adults) found CBT-I, a structured talking-and-habits program, reduced insomnia severity by a large amount in people with heavy alcohol use or alcohol use disorder. Alcohol-related outcomes were not reliably changed. Guidelines list CBT-I first for chronic insomnia.
1 studiesCBT-I delivered as in each trial; not described in the abstract.
Studies, doses and limits
What the trials found
Meta-analysis of 8 randomised trials, 426 adults, 68.78% men (Türkmen 2025).
Results
Insomnia Severity Index fell by 5.51 points versus control after treatment, 4.39 at 1 to 3 months and 4.55 at 6 months. No significant differences in craving, drinking days or alcohol problems.
Effect sizes as reported
ISI -5.51 (CI -7.13 to -3.90)
Why this rating
Moderate, the compiler's rating: 8 trials of low or moderate bias but a small total sample and no alcohol-outcome benefit.
Form and dose studied
CBT-I delivered as in each trial; not described in the abstract.
Who was studied
Adults with insomnia and heavy drinking or alcohol use disorder.
Limits
Small total sample, mostly men, alcohol outcomes inconsistent.
Why researchers looked
Insomnia is common in alcohol use disorder and may raise the risk of relapse.
Proposed mechanism Hypothesis
Proposed: treating insomnia may support recovery. Not shown by the alcohol outcomes.
A proposed mechanism does not show that the effect happens in people.
Anyone who drinks heavily should ask a doctor before stopping suddenly.
Stopping smoking and sleep
Low certaintyA 2025 review found sleep changes persist for the first few weeks of withdrawal and predict relapse, with some sleep restoration in people using nicotine patches. An older review of 52 studies found nicotine use goes with trouble falling asleep, fragmented sleep, less deep sleep and less REM sleep. The NHS lists smoking among things to avoid for 6 hours before bed.
3 studiesNicotine replacement products as used in each study; not advice.
Studies, doses and limits
What the trials found
Systematic review of studies comparing sleep before and after quitting (Mauries 2025); descriptive review of 52 studies (Jaehne 2009).
Results
Without nicotine replacement, light sleep fell in those staying quit for 6 months and REM fell only in those who relapsed. Long-term patches were linked with more deep sleep than short-acting patches in one study. Findings were heterogeneous.
Effect sizes as reported
Not given as numbers
Why this rating
Low, the compiler's rating: heterogeneous small studies, mostly observational, and older descriptive data.
Form and dose studied
Nicotine replacement products as used in each study; not advice.
Who was studied
Smokers, with and without cessation treatment.
Limits
Different measures, small studies, withdrawal masks effects.
Why researchers looked
Nicotine is a stimulant and withdrawal disturbs sleep, so researchers studied what happens when people quit.
Proposed mechanism Hypothesis
Proposed in the 2009 review: nicotine acts on several brain chemicals that regulate sleep.
A proposed mechanism does not show that the effect happens in people.
Quitting can cause temporary sleep trouble; a GP or pharmacist can help with a quit plan.
A behavioural sleep program for smokers with insomnia
Very low certaintyIn a pilot of 19 smokers with insomnia, adding CBT-I to smoking-cessation counselling improved sleep efficiency, quality, duration and insomnia symptoms, but quit rates were low in both groups and did not differ.
1 studies8 sessions over 10 weeks plus a nicotine patch for 6 weeks, as report…
Studies, doses and limits
What the trials found
Randomised pilot study, 19 smokers with insomnia (Fucito 2014).
Results
Sleep improved in the CBT-I group; 7-day abstinence at end of treatment 14% versus 20% (not different).
Effect sizes as reported
Not given as numbers
Why this rating
Very low, the compiler's rating: 19 people, no significant smoking effect.
Form and dose studied
8 sessions over 10 weeks plus a nicotine patch for 6 weeks, as reported.
Who was studied
Adults seeking to quit who had insomnia.
Limits
Very small pilot; the authors call for a larger trial.
Why researchers looked
Poor sleep predicts quitting failure, so researchers tested adding sleep treatment.
Proposed mechanism Hypothesis
Not tested.
A proposed mechanism does not show that the effect happens in people.
Nicotine patches can affect sleep in some people; ask a pharmacist.
Electronic cigarettes and sleep
Very low certaintyA 2025 meta-analysis of 14 cross-sectional studies found e-cigarette users had higher odds of short sleep duration (OR 1.38) than non-users. Among adolescents inadequate sleep was 33 to 61 percent more likely. Surveys cannot show whether vaping causes poor sleep.
1 studiesNot a dosing study.
Studies, doses and limits
What the trials found
Meta-analysis of 14 cross-sectional studies (Sulthana 2025).
Results
Short sleep duration OR 1.38 (CI 1.24 to 1.55); also more insomnia and use of sleep medication in several studies.
Effect sizes as reported
OR 1.38 for shorter sleep
Why this rating
Very low, the compiler's rating: cross-sectional only, with the authors calling for long-term studies.
Form and dose studied
Not a dosing study.
Who was studied
Adults and adolescents.
Limits
Cross-sectional data cannot separate cause and effect.
Why researchers looked
Vaping delivers nicotine, and researchers wondered whether it affects sleep like smoking does.
Proposed mechanism Hypothesis
Not tested.
A proposed mechanism does not show that the effect happens in people.
E-cigarettes deliver nicotine; ask a clinician for evidence-based help to quit.
Connections to the rest of health
How Caffeine, Alcohol, Nicotine and Sleep connects to the rest of our health knowledge graph. Every link says what kind of connection it is. A safety link (for example to the liver) is a warning, not a benefit. A study that merely mentions a topic never creates a benefit link.
Explore every connection: goals, body systems, organs, symptoms, genes
A. Wellness goals
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Better Sleep | Moderate certainty | Stopping caffeine hours before bed: A 2023 meta-analysis of 24 studies found caffeine cut total sleep time by about 45 minutes and sleep efficiency by 7 percent. A home trial found 400 mg disrupted sleep even when taken 6 hours before bed, and a later crossover trial found the disruption grew the closer the dose was to bedtime. The NHS advises no tea or coffee for at least 6 hours before bed. Evening caffeine before training: A 2025 review of 10 studies of 128 athletes found a small drop in sleep efficiency (about 5 percent) after evening caffeine in randomised trials, but the result was not robust and total sleep time change was not significant. Athletes felt their sleep was clearly worse even when the measurements did not always show it. | 5 3 6 26 23 12 7 21 24 13 2 17 25 19 | |
| Better Sleep | Low certainty | A smaller caffeine dose: In a randomised crossover trial of 23 men, a 100 mg dose of caffeine had no significant effect on sleep even when taken 4 hours before bed, while 400 mg did. In 18 teenage boys, 80 mg taken 4 hours before bed did not strongly cut deep sleep or sleep quality on average, but some teens lost deep sleep. Regular bedtime caffeine and partial tolerance: In 19 good sleepers given 250 mg at bedtime for five days, most of the sleep disruption showed up on the first night, and only lower sleep efficiency lasted the week. Partial tolerance seemed to develop. That is not a reason to take caffeine near bedtime: sleep was still worse than on placebo. | 6 16 23 10 4 | |
| Better Sleep | Low certainty | Knowing your own caffeine sensitivity: A 2023 review of 22 reports found that variation in the ADORA2A gene was linked with anxiety and sleep problems after caffeine, and variation in CYP1A2 with thinking tasks. This may explain why some people sleep fine after an espresso and others do not, but gene testing is not a proven way to pick a cut-off time. Stopping smoking and sleep: A 2025 review found sleep changes persist for the first few weeks of withdrawal and predict relapse, with some sleep restoration in people using nicotine patches. An older review of 52 studies found nicotine use goes with trouble falling asleep, fragmented sleep, less deep sleep and less REM sleep. The NHS lists smoking among things to avoid for 6 hours before bed. | 9 26 14 8 | |
| Better Sleep | Very low certainty | Reducing caffeine and energy drinks in teenagers: In a 2024 meta-analysis of studies of adolescents, higher caffeine intake went with higher odds of sleep problems (odds ratio 1.67). A UK-commissioned overview found that frequent energy drink use (5 or more days a week) went with sleep problems, headaches and other problems, but the evidence is weak and cannot show cause. No trial of cutting down was read. Electronic cigarettes and sleep: A 2025 meta-analysis of 14 cross-sectional studies found e-cigarette users had higher odds of short sleep duration (OR 1.38) than non-users. Among adolescents inadequate sleep was 33 to 61 percent more likely. Surveys cannot show whether vaping causes poor sleep. | 22 11 23 18 | |
| Better Sleep | Mixed findings | Do alcohol and smoking cause insomnia? Genetic evidence: A genetic (Mendelian randomisation) study found strong evidence that insomnia raises the chance of alcohol dependence, smoking and cannabis use, that smoking initiation raises insomnia risk, and no evidence that alcohol per week or alcohol dependence causes insomnia. This does not match what sleep labs show about alcohol and night-time sleep, so the picture is mixed. | 15 |
B. Body systems
E. Health conditions
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Sleep apnea | Health agency guidance | Alcohol worsens breathing pauses and oxygen levels in sleep, most in people who snore or have sleep apnea. Preparation or compound: Alcohol |
25 13 | |
| Insomnia | Health agency guidance | The NHS lists alcohol, caffeine and nicotine among the most common causes of insomnia. Preparation or compound: Caffeine, alcohol, nicotine |
26 | |
| Insomnia | Health agency guidance | The NHS lists them among common causes of insomnia. Preparation or compound: Caffeine, alcohol, nicotine |
26 | |
| Sleep apnea | Moderate certainty | Meta-analyses link alcohol with more breathing pauses. Preparation or compound: Alcohol |
13 2 |
I. Biomarkers
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Total sleep time | Biological association | Moderate certainty | Measured in trials: Longer is better. A lab change is not the same as a health benefit. | 5 3 |
| Time to fall asleep (sleep onset latency) | Biological association | Moderate certainty | Measured in trials: Shorter is better. A lab change is not the same as a health benefit. | 5 6 |
| Breathing pauses per hour (apnea-hypopnea index, AHI) | Biological association | Moderate certainty | Measured in trials: Lower is better. A lab change is not the same as a health benefit. | 13 2 |
| REM (dream) sleep | Biological association | Moderate certainty | Measured in trials: Not in itself better or worse; reduction is the concern. A lab change is not the same as a health benefit. | 7 8 |
L. Active compounds
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Caffeine | Biological association | Human | Stimulant; the 2024 review says it blocks adenosine receptors. | 23 5 |
| Alcohol (ethanol) | Biological association | Human | May shorten time to fall asleep at high doses; reduces REM sleep and worsens breathing in sleep. | 7 13 |
| Nicotine | Biological association | Human | Linked with longer time to fall asleep, fragmented sleep and less deep and REM sleep. | 8 |
Each connection is stored with the ingredient, the connected record, the kind of connection, the evidence status, the supporting studies, the preparation or compound involved, and a review date (last reviewed October 31, 2026).
Evidence at a glance: what the research found for 13 outcomes
Each outcome below is one thing researchers measured. Certainty is how far the evidence can be trusted, not how well it works. The full studies are on the next tab.
The evidence
The research centre for Caffeine, Alcohol, Nicotine and Sleep. Every record here was checked against PubMed or the publisher's page; we never list a study we have not verified.
Evidence by outcome
Bars show how many studies we found for each outcome, not how well it works. People are added up across trials only (reviews are not added, to avoid double counting).
How we rate evidence
High certainty
Several well-run trials or reviews agree; further research is unlikely to change the picture much.
Moderate certainty
Good trials point the same way, but some doubt remains.
Low certainty
Small, short or inconsistent trials. The finding could change with better research.
Very low certainty
Very little or very weak human data. Treat as a possibility only.
Mixed findings
Trials or reviews disagree with each other.
Not enough evidence
Not enough human research to say either way.
Evidence against
Good research found no benefit, or found harm.
We take the reviewers' own risk-of-bias and GRADE statements where they exist, and otherwise judge from study size, design, consistency, directness and whether a product matches what is sold. Many publications do not make evidence high. Method note: We searched PubMed, re-read the abstract of every review and trial cited, and read the NHS, NHLBI and FDA pages through a tool that summarises pages. Full texts were not read. Certainty ratings are the compiler's own reading. Funding is not stated in most abstracts, and this is noted where relevant.
Study library: every study we checked 27
| Study | Design | People | Product, dose, length | Result |
|---|---|---|---|---|
| Bagheri Davisaraei 2024 Coffee and sleep: Benefits and risks Prog Brain Res · PMID 39168560 · DOI |
Narrative review |
Review of coffee and sleep | Coffee and caffeine Not given · vs Not given |
Caffeine slows sleep onset, blocks adenosine receptors, lowers deep sleep and REM sleep; sensitive people are more affected. Narrative (Not given) Methods, limits and fundingOutcomes: Sleep onset, deep sleep, REM Limitations: Narrative review, no data pooled. Funding and conflicts: Not stated in the abstract. Read: abstract |
| Burgos-Sanchez 2020 Impact of Alcohol Consumption on Snoring and Sleep Apnea: A Systematic Review and Meta-analysis Otolaryngol Head Neck Surg · PMID 32513091 · DOI |
Systematic review meta analysis |
279 13 studies with polysomnography data, 279 people |
Alcohol Not given · vs Control without alcohol |
AHI mean difference 3.98 events per hour; lowest oxygen saturation -2.72%. AHI MD 3.98; LSAT MD -2.72% (AHI 3.27 to 4.68; LSAT -3.69 to -1.76) Methods, limits and fundingOutcomes: AHI, lowest oxygen saturation, snoring, sleep stages Limitations: Only sleep-lab data; small studies. Funding and conflicts: Registered with PROSPERO. Read: abstract |
| Drake 2013 Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed J Clin Sleep Med · PMID 24235903 · DOI |
Randomised controlled trial |
Adults sleeping in their own homes (number not given in the abstract) | 400 mg caffeine Single doses at 0, 3 and 6 hours before habitual bedtime · vs Placebo |
400 mg at bedtime, 3 h or 6 h before bed each had significant effects on sleep disturbance versus placebo (p<0.05); the loss of total sleep time was large enough that 6 hours has important effects. Significant versus placebo (p<0.05) (Not given in the abstract) Methods, limits and fundingOutcomes: Self-reported sleep and sleep-monitor disturbance Limitations: Sample size not stated in the abstract; single large dose. Funding and conflicts: Not stated in the abstract. Read: abstract |
| Fucito 2014 Integrating a Behavioural Sleep Intervention into Smoking Cessation Treatment for Smokers with Insomnia: A Randomised Pilot Study J Smok Cessat · PMID 24995044 · DOI |
Randomised controlled trial |
19 19 smokers with insomnia seeking to quit |
CBT-I plus smoking-cessation counselling 8 sessions over 10 weeks; nicotine patch 6 weeks · vs Counselling alone |
No significant difference in quitting; sleep improved in the CBT-I group. Abstinence 14% versus 20% at end of treatment (Not given) Methods, limits and fundingOutcomes: Smoking abstinence, sleep efficiency and quality Limitations: Pilot with 19 people. Funding and conflicts: Not stated in the abstract. Read: abstract |
| Gardiner 2023 The effect of caffeine on subsequent sleep: A systematic review and meta-analysis Sleep Med Rev · PMID 36870101 · DOI |
Systematic review meta analysis |
24 studies of caffeine and night-time sleep | Caffeine (coffee, pre-workout and others) Not given in the abstract · vs Placebo or no caffeine |
Caffeine reduced total sleep time by 45 min and sleep efficiency by 7%; time to fall asleep +9 min; wake after sleep onset +12 min; light sleep up, deep sleep down. Coffee (107 mg per 250 mL) should be taken at least 8.8 h before bed. Total sleep time -45 min; sleep efficiency -7% (Not given in the abstract) Methods, limits and fundingOutcomes: Total sleep time, sleep efficiency, time to fall asleep, time awake after sleep onset, sleep stages Limitations: Study sizes and populations not given in the abstract; the cut-off time is a model estimate. Funding and conflicts: Not stated in the abstract. Read: abstract |
| Gardiner 2025 Dose and timing effects of caffeine on subsequent sleep: a randomized clinical crossover trial Sleep · PMID 39377163 · DOI |
Randomised controlled trial |
23 23 men aged 25.3 (SD 5.0) with moderate habitual intake (under 300 mg a day) |
Caffeine 100 mg and 400 mg 12, 8 or 4 hours before bed; 48-hour washout · vs Placebo |
100 mg: no significant effect. 400 mg within 12 h of bed delayed sleep and altered sleep stages; within 8 h more fragmentation; perceived sleep quality fell 34% when taken 4 h before bed. People misjudged the effect. Perceived sleep quality -34.02% (p=.006) with 400 mg at 4 h (Not given in the abstract) Methods, limits and fundingOutcomes: Home partial polysomnography and sleep diaries Limitations: Men only, one night per condition, healthy and moderate users. Funding and conflicts: Registered ACTRN12621001625864; funding not stated in the abstract. Read: abstract |
| Gardiner 2025 The effect of alcohol on subsequent sleep in healthy adults: A systematic review and meta-analysis Sleep Med Rev · PMID 39631226 · DOI |
Systematic review meta analysis |
27 studies in healthy adults | Alcohol, at different doses and times Not given in the abstract · vs Placebo or none |
REM delayed and reduced after about two drinks and worse with dose; sleep onset shorter only after about five drinks; other effects uncertain. Dose-response for REM; no numbers in the abstract (Not given in the abstract) Methods, limits and fundingOutcomes: REM sleep, sleep onset latency, N3 latency, total sleep time, efficiency Limitations: Large uncertainty for total sleep time and efficiency. Funding and conflicts: Not stated in the abstract. Read: abstract |
| Jaehne 2009 Effects of nicotine on sleep during consumption, withdrawal and replacement therapy Sleep Med Rev · PMID 19345124 · DOI |
Systematic review |
52 studies in animals and humans | Nicotine use, withdrawal and replacement Not given · vs Not given |
During use: longer sleep latency, fragmentation, less slow-wave sleep and efficiency; most studies showed REM suppression; replacement effects masked by withdrawal; smoking linked with more sleep-related breathing disorders. Descriptive (Not given) Methods, limits and fundingOutcomes: Sleep latency, fragmentation, deep and REM sleep Limitations: Descriptive overview; different methods across studies. Funding and conflicts: Not stated in the abstract. Read: abstract |
| Kapellou 2023 Genetics of caffeine and brain-related outcomes - a systematic review of observational studies and randomized trials Nutr Rev · PMID 37029915 · DOI |
Systematic review |
22 reports in healthy adults (15 randomised trials, 6 cross-sectional, 1 genome-wide study) | Caffeine intake or supplementation and gene variants (CYP1A2, ADORA2A) Not given · vs Not part of the design |
ADORA2A variants were associated with anxiety and sleep disturbance; CYP1A2 variants with cognitive function. Associations, no numbers in the abstract (Not given in the abstract) Methods, limits and fundingOutcomes: Cognition, anxiety, sleep disturbance and insomnia Limitations: Mixed designs; not tested as a guide to personal advice. Funding and conflicts: Registered CRD42021257556. Read: abstract |
| Keenan 2014 Naturalistic Effects of Five Days of Bedtime Caffeine Use on Sleep, Next-Day Cognitive Performance, and Mood J Caffeine Res · PMID 24868491 · DOI |
Randomised controlled trial |
19 19 good sleepers with usual caffeine intake of 0 to 141 mg a day |
250 mg caffeine at bedtime 5 days in a 2-week crossover · vs Placebo |
Sleep disrupted mainly on day 1; only lower sleep efficiency persisted over the week; partial tolerance. Working memory better after caffeine, likely reversing overnight withdrawal. Not given as numbers (Not given in the abstract) Methods, limits and fundingOutcomes: Actigraphy, sleep diary, next-day performance and mood Limitations: Small, good sleepers, low usual intake. Funding and conflicts: Not stated in the abstract. Read: abstract |
| Khouja 2022 Consumption and effects of caffeinated energy drinks in young people: an overview of systematic reviews and secondary analysis of UK data to inform policy BMJ Open · PMID 35131813 · DOI |
Systematic review |
Overview of 15 systematic reviews plus 5 UK datasets of under-18s | Caffeinated energy drinks Frequent use = 5 or more days a week · vs Non-users |
Frequent drinking was associated with low well-being; drinking was associated with headaches, sleep problems, alcohol use, smoking and irritability. Evidence is weak. Associations only (Not given in the abstract) Methods, limits and fundingOutcomes: Health and behaviour including sleep problems Limitations: Review quality rated low or critically low; surveys cannot show cause. Funding and conflicts: Registered CRD42018096292 and CRD42018110498. Read: abstract |
| Kocak 2025 The Effect of Consuming Caffeine Before Late Afternoon/Evening Training or Competition on Sleep: A Systematic Review with Meta-Analysis Sports (Basel) · PMID 41003623 · DOI |
Systematic review meta analysis |
128 10 studies of 128 athletes |
Caffeine 3 to 6 mg per kg body weight before evening training Not given in the abstract · vs Placebo or none |
Sleep efficiency -4.87% (not robust); total sleep time -32.47 min (not significant); athletes reported substantial sleep impairment. Sleep efficiency MD -4.87%; total sleep time MD -32.47 min (Sleep efficiency CI -7.45 to -2.29; total sleep time CI -69.93 to 4.99) Methods, limits and fundingOutcomes: Sleep efficiency, total sleep time, subjective sleep Limitations: Few studies, mostly male athletes; results not robust. Funding and conflicts: Not stated in the abstract. Read: abstract |
| Kolla 2018 The impact of alcohol on breathing parameters during sleep: A systematic review and meta-analysis Sleep Med Rev · PMID 30017492 · DOI |
Systematic review meta analysis |
422 14 studies, 422 people (71.9% male) |
Alcohol administration Not given · vs Before versus after alcohol / control |
AHI +2.33; SpO2 -0.60%; larger in snorers (+4.20) and people with sleep apnea (+7.10). AHI WMD 2.33 (1.41 to 3.25) Methods, limits and fundingOutcomes: AHI and oxygen saturation Limitations: Mostly male; moderate heterogeneity. Funding and conflicts: Not stated in the abstract. Read: abstract |
| Mauries 2025 Conditions of sleep restoration after smoking cessation: A systematic review Sleep Med Rev · PMID 39893864 · DOI |
Systematic review |
Studies comparing sleep before and after quitting, and relapsers versus abstainers | Smoking cessation with or without medication or therapy Up to 6 months in some studies · vs Relapse versus abstinence |
Without NRT, N1 reduced after 6 months of abstinence; REM reduced only in relapsers; sleep alterations persist the first weeks and predict relapse; some restoration with NRT. Not given (Not given) Methods, limits and fundingOutcomes: Sleep stages and subjective sleep Limitations: Heterogeneous results; limited data. Funding and conflicts: Not stated in the abstract. Read: abstract |
| Pasman 2020 Causal relationships between substance use and insomnia Drug Alcohol Depend · PMID 32634714 · DOI |
Mendelian randomisation |
Genome-wide association study data on insomnia, smoking, alcohol and cannabis | Genetic liability to substance use or insomnia Not part of the design · vs Not part of the design |
Insomnia liability raised smoking traits, alcohol dependence and cannabis initiation; smoking initiation raised insomnia risk; no evidence that drinks per week, alcohol dependence or cannabis initiation caused insomnia. Not given in the abstract (Not given in the abstract) Methods, limits and fundingOutcomes: Causal effects in both directions Limitations: Genetic liability is not the same as one evening's use. Funding and conflicts: Not stated in the abstract. Read: abstract |
| Reichert 2021 Wide awake at bedtime? Effects of caffeine on sleep and circadian timing in male adolescents - A randomized crossover trial Biochem Pharmacol · PMID 33069664 · DOI |
Randomised controlled trial |
18 18 male teenagers aged 14 to 17 after 6 days of caffeine abstinence |
80 mg caffeine Once, 4 hours before an EEG-recorded night · vs Placebo |
Sleepiness fell with caffeine. No strong group reduction in deep sleep or sleep quality, but large person-to-person differences; those with more deep sleep on placebo lost more. Melatonin delays only above 1.3 mg per kg. Not given as numbers (Not given in the abstract) Methods, limits and fundingOutcomes: Deep (slow-wave) sleep, subjective sleep quality, melatonin onset Limitations: Boys only; one dose and one night; in the lab. Funding and conflicts: Not stated in the abstract. Read: abstract |
| Simou 2018 Alcohol and the risk of sleep apnoea: a systematic review and meta-analysis Sleep Med · PMID 29458744 · DOI |
Systematic review meta analysis |
21 comparative epidemiological studies in adults | Higher alcohol consumption Not part of the design · vs Lower consumption |
Higher alcohol consumption increased risk by 25%; average intake only two units a week higher in people with apnoea (not significant); publication bias detected. RR 1.25 (1.13 to 1.38) Methods, limits and fundingOutcomes: Risk of sleep apnoea Limitations: High heterogeneity (I2 82%) and publication bias. Funding and conflicts: Not stated in the abstract. Read: abstract |
| Sulthana 2025 Impact of electronic cigarette use and sleep duration, sleep issues and insomnia: a systematic review and meta-analysis Front Public Health · PMID 40951402 · DOI |
Systematic review meta analysis |
14 cross-sectional studies | E-cigarette use Not part of the design · vs Non-users |
Shorter sleep duration OR 1.38 for users; more insomnia and sleep-medication use in several studies; adolescents 33 to 61% more likely to have inadequate sleep. OR 1.38 (1.24 to 1.55) Methods, limits and fundingOutcomes: Sleep duration, insomnia, sleep medication use Limitations: Cross-sectional only. Funding and conflicts: Not stated in the abstract. Read: abstract |
| Türkmen 2025 Cognitive behavioral therapy for insomnia across the spectrum of alcohol use disorder: A systematic review and meta-analysis Sleep Med Rev · PMID 39864131 · DOI |
Systematic review meta analysis |
426 8 randomised trials, 426 adults (68.78% men) with heavy alcohol use or alcohol use disorder and insomnia |
CBT-I Post-treatment and follow-up at 1 to 3 and 6 months · vs Control conditions |
ISI fell 5.51 post-treatment, 4.39 at 1 to 3 months, 4.55 at 6 months; alcohol outcomes not significantly different. ISI -5.51 (-7.13 to -3.90) Methods, limits and fundingOutcomes: Insomnia Severity Index, craving, drinking days Limitations: Small sample; alcohol outcomes inconsistent. Funding and conflicts: Registered CRD42023464612. Read: abstract |
| Vanderkam 2024 Insomnia and parasomnia induced by validated smoking cessation pharmacotherapies and electronic cigarettes: a network meta-analysis CNS Spectr · PMID 38433577 · DOI |
Systematic review meta analysis |
37 randomised trials of adult smokers without unstable or psychiatric comorbidity | Varenicline, nicotine replacement, bupropion Not given in the abstract · vs Placebo or other cessation methods |
Insomnia and parasomnia were more frequent with cessation therapies than placebo except bupropion; insomnia was less frequent with nicotine substitutes; no e-cigarette trials were included. Not given in the abstract (Not given in the abstract) Methods, limits and fundingOutcomes: Insomnia and parasomnia Limitations: Sleep reported as side effects; no e-cigarette studies. Funding and conflicts: Not stated in the abstract. Read: abstract |
| Zheng 2021 Alcohol consumption and sleep quality: a community-based study Public Health Nutr · PMID 33183388 · DOI |
Cross sectional |
11905 11,905 adults in the Kailuan community, China |
Alcohol intake (none, light, moderate, heavy) Intake 2006 and 2012; sleep 2012 · vs Non-drinkers |
Dose-response link between more alcohol and worse sleep quality; heavy drinkers had higher odds of short sleep (OR 1.31) and snoring (OR 1.38); hard liquor, not beer or wine, linked to poor sleep. Short sleep OR 1.31; snoring OR 1.38 (1.09 to 1.57; 1.22 to 1.57) Methods, limits and fundingOutcomes: Insomnia, daytime sleepiness, sleep duration, snoring or sleep apnoea Limitations: Cross-sectional; single community. Funding and conflicts: Not stated in the abstract. Read: abstract |
| Zhong 2024 Modifiable dietary factors in adolescent sleep: A systematic review and meta-analysis Sleep Med · PMID 38350307 · DOI |
Systematic review meta analysis |
33 publications of adolescents aged 12 to 18; meta-analysis of 6 studies | Dietary factors, including caffeine and alcohol intake Usual intake · vs Lower intake |
Higher caffeine intake: odds of sleep problems OR 1.67; alcohol: odds of insomnia OR 1.17. OR 1.67 (caffeine); OR 1.17 (alcohol) (1.28 to 2.17 (caffeine); 1.07 to 1.27 (alcohol)) Methods, limits and fundingOutcomes: Sleep problems and insomnia Limitations: Mostly cross-sectional, self-reported, high differences between studies. Funding and conflicts: Not stated in the abstract. Read: abstract |
| s-fda-caffeine FDA: Spilling the Beans, How Much Caffeine Is Too Much? (content current as of 28 August 2024) · Source |
Health agency n/a |
Methods, limits and fundingRead: full-text | ||
| s-nhlbi-treatment NHLBI: Insomnia treatment (last updated 24 March 2022) · Source |
Health agency n/a |
Methods, limits and fundingRead: full-text | ||
| s-nhs-apnoea NHS: Sleep apnoea (last reviewed 11 May 2026) · Source |
Health agency n/a |
Methods, limits and fundingRead: full-text | ||
| s-nhs-insomnia NHS: Insomnia (last reviewed 19 March 2024) · Source |
Health agency n/a |
Methods, limits and fundingRead: full-text | ||
| s-nhs-pregnancy NHS: Foods to avoid in pregnancy (last reviewed 15 June 2026) · Source |
Health agency n/a |
Methods, limits and fundingRead: full-text |
What we do not know yet
- No randomised trial of cutting out an evening drink in people with insomnia was read.
- Nicotine replacement and vaping effects on sleep in trials were not found in the sources read.
- No trial of people with insomnia who cut caffeine back was read.
- Most caffeine trials are in young, healthy people, often men, with a single large dose.
- Nicotine replacement and vaping effects on sleep in randomised trials were not found.
How new research is added
New studies are found by a saved PubMed search and placed in a review queue before the page changes.
Lab markers
What changed in blood or saliva tests during trials. A changed number is not the same as feeling or being healthier, and we give no "normal ranges".
Other 4
Total sleep time
Longer is better in trials
How long you actually sleep, measured by a sleep monitor or diary.
Moderate certaintyResults and what it means
Why it was measured
To see whether caffeine timing changes how much sleep you get.
Statistical vs. clinical meaning
A clear loss in the pooled analysis; sizes vary by dose and timing.
Time to fall asleep (sleep onset latency)
Shorter is better in trials
How long it takes to fall asleep.
Moderate certaintyResults and what it means
Why it was measured
To see whether stimulants delay sleep.
Statistical vs. clinical meaning
Delay is modest but consistent.
Breathing pauses per hour (apnea-hypopnea index, AHI)
Lower is better in trials
How many breathing pauses or shallow breaths happen per hour of sleep.
Moderate certaintyResults and what it means
Why it was measured
To see whether alcohol worsens breathing in sleep.
Statistical vs. clinical meaning
A clinically relevant rise in people who already have sleep apnea.
REM (dream) sleep
Not in itself better or worse; reduction is the concern in trials
The stage of sleep with vivid dreams, thought to matter for memory and mood.
Moderate certaintyResults and what it means
Why it was measured
To see how alcohol and nicotine change the structure of sleep.
Statistical vs. clinical meaning
Consistent change across studies; the long-term effect was not measured in the abstracts.
Safety
What studies and official sources say about side effects, medicines and who should check first. Each point shows what kind of evidence it comes from.
Main points to know 7
- See a doctor if poor sleep lasts, or if you rely on caffeine, alcohol or nicotine to cope. The NHS says to see a GP if changing sleep habits has not helped, if trouble sleeping has lasted months, or if insomnia makes it hard to cope day to day. Alcohol, caffeine or nicotine are among its common causes of insomnia. Do not stop drinking suddenly if you drink heavily without advice, because withdrawal can be dangerous. Health agency guidance 26
- Loud snoring, gasping or breathing pauses may be sleep apnoea. The NHS lists breathing that stops and starts, gasping, snorting or choking noises and always feeling very tired in the day as reasons to see a GP, and advises against drinking too much alcohol, especially shortly before sleep. Meta-analyses find alcohol worsens breathing pauses and oxygen levels, most in people who snore or have sleep apnea. Health agency guidance and meta analysis 25 13 2
- Too much caffeine: signs and who is at higher risk. The FDA lists fast heart rate, palpitations, high blood pressure, insomnia, anxiety, jitters, upset stomach, nausea and headache as signs of too much caffeine and suggests talking to a health professional if they occur. It says certain medical conditions and some medicines can make people more sensitive. Decaf is not caffeine-free. Health agency guidance 23
- Children and teens: avoid energy drinks. The FDA says medical experts advise against energy drinks for children and teens and that too much caffeine can cause fast heart rate, high blood pressure, anxiety and sleep problems. A UK overview found weak evidence linking frequent energy drink use with sleep problems and headaches. Health agency guidance and systematic review 23 11
- Pregnancy and breastfeeding. The NHS advises no more than 200 mg of caffeine a day in pregnancy and says it is safest to avoid alcohol. The FDA advises anyone pregnant, trying to become pregnant or breastfeeding to talk with a health care provider about limiting caffeine. Ask a clinician before using any nicotine product, including patches. Health agency guidance 27 23
- Alcohol is not a safe sleep aid. The NHLBI notes alcohol can make it easier to fall asleep but can lead to lighter sleep and more waking. Reviews find it reduces REM sleep even at low doses. Combining alcohol with sleep medicines, antihistamines or melatonin can add sleepiness; ask a pharmacist. This page does not recommend any medicine. Health agency guidance and meta analysis 24 7
- Not a replacement for care. This page describes studies and agency guidance. It does not replace advice from a clinician, especially for dependence on alcohol or nicotine, for people with heart conditions or anxiety, and for anyone taking medicines. Editorial 26
Side effects 5
| Effect | How often | Severity and recovery | Evidence |
|---|---|---|---|
| Insomnia, jitters, fast heartbeat, anxiety from too much caffeine Listed by the FDA among signs of too much caffeine. | Not given | Mild to moderate Not stated | Health agency guidance 23 |
| Poorer sleep quality and less REM sleep from evening alcohol Even about two drinks reduced REM sleep in the pooled data. | Dose-related in meta-analysis | Mild to moderate Not stated | Systematic review 7 |
| More breathing pauses and lower oxygen at night Greater in snorers and people with sleep apnea. | Average rise of about 2 to 7 events an hour | Can be serious in sleep apnea Not stated | Meta analysis of randomised trials 13 |
| Sleep trouble during the first weeks of quitting smoking Sleep alterations predicted relapse in the studies reviewed. | Not given | Mild to moderate Persists for the first few weeks in studies | Systematic review 14 |
| Insomnia and unusual dreams from smoking cessation medicines A clinician can discuss options; not recommended here. | More frequent than placebo for most | Mild to moderate Not stated | Network meta analysis 20 |
Medicines and supplements 2
| With | Why it matters | Importance | Evidence | What to do |
|---|---|---|---|---|
| Other sedating products (alcohol, antihistamines, sleep aids) general | Could add to drowsiness | The NHS advises not drinking alcohol when taking some sleep products; this page covers no specific medicine. | Health agency guidance Not enough evidence 26 | Ask a pharmacist before mixing alcohol with any medicine. |
| Caffeine and conditions or medicines that raise sensitivity general | Some conditions and medicines make people more sensitive to caffeine | The FDA says this without naming specific ones in the page read. | Health agency guidance Not enough evidence 23 | Ask a clinician if you take regular medicines and notice jitters or palpitations. |
Who should check first 3
| Situation | Advice | Evidence |
|---|---|---|
| Pregnancy | NHS: keep caffeine to 200 mg a day or less; it is safest to avoid alcohol. | Health agency guidance 27 |
| Children and teenagers | The FDA says experts advise against energy drinks for them. | Health agency guidance 23 |
| Heavy or dependent drinking | Withdrawal can be dangerous; speak to a doctor before stopping suddenly. CBT-I has been studied in this group (see Benefits). | Systematic review 19 |
Overdose, product quality and regulators
| Body | Action | Date |
|---|---|---|
| U.S. Food and Drug Administration (FDA) (United States) | Cites 400 mg a day as an amount not generally associated with negative effects in most adults, with wide differences in sensitivity; advises against energy drinks for children and teens. source | 2024-08 |
| National Health Service (NHS) (United Kingdom) | Advises no smoking, alcohol, tea or coffee at least 6 hours before bed; caffeine limit 200 mg a day in pregnancy. source | 2024-03 |
When to get medical help
- Chest pain, a racing or irregular heartbeat that does not settle, fainting or severe shortness of breath after caffeine, energy drinks or nicotine: seek emergency care now.
- Thoughts of harming yourself, or feeling unable to keep yourself safe: contact your local emergency number or a crisis line in your country now, or go to the nearest emergency department.
- Heavy daily drinking followed by shaking, sweating, confusion, seeing things that are not there, or seizures after stopping: seek emergency care.
- Loud snoring, gasping or breathing pauses, or falling asleep during the day without warning: see a doctor, because sleep apnea may be the cause.
- Sleep problems that last months or make work, driving or daily life hard: book a doctor visit, as the NHS advises.
Stop using the product and contact a clinician or emergency service. In the US, Poison Control is 1-800-222-1222.
General information only, not medical advice. Ask a clinician or pharmacist before use, especially with medicines, in pregnancy or with a health condition. See the Natural Remedy Safety guide.
Frequently asked questions
How many hours before bed should I stop caffeine?
How does caffeine affect sleep?
Pooled studies found about 45 minutes less sleep, 7 percent lower sleep efficiency, and less deep sleep.
Does alcohol help you sleep?
How long before bed should I stop drinking alcohol?
Does smoking or nicotine affect sleep?
Will my sleep improve if I quit smoking?
Sleep stays disturbed for the first few weeks and predicts relapse, then some restoration was seen, especially with nicotine patches. Ask a GP or pharmacist for help.
Does vaping affect sleep?
E-cigarette users had higher odds of short sleep (OR 1.38) in cross-sectional studies; cause cannot be shown.
Does alcohol make sleep apnea worse?
Is decaf coffee okay before bed?
Decaf is not caffeine-free; the FDA says it typically has 2 to 15 mg per 8 fl oz cup. No trial of decaf and sleep was read beyond a 6-person study from 2002, so no conclusion is drawn.
How much caffeine is too much?
Are energy drinks a problem for teens?
Explore by health goal
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- Written by
- AlternativeMed editorial team. Research compiled with AI assistance, then checked against PubMed records.
- Medical review
- None. This page has not been reviewed by a physician or pharmacist.
- First published
- 2026-10-22
- Last substantive update
- 2026-10-31
- How we research
- We searched PubMed, re-read the abstract of every review and trial cited, and read the NHS, NHLBI and FDA pages through a tool that summarises pages. Full texts were not read. Certainty ratings are the compiler's own reading. Funding is not stated in most abstracts, and this is noted where relevant.
- How we rate evidence
- See "How we rate evidence" in the Evidence tab.
- Independence
- No product is promoted on this page. No affiliate links are shown.
Sources 27
Each source was opened and checked. Where we read only the abstract, it says so. The small numbers in the text point here.
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- . FDA: Spilling the Beans, How Much Caffeine Is Too Much? (content current as of 28 August 2024). . . (full-text)
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