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Caffeine and Medicines: Interactions Pharmacists Check

How caffeine and some medicines affect each other, what small studies found for antibiotics, antidepressants, thyroid and other medicines, and what to ask a pharmacist.

Content last updated . This page has not been medically reviewed.

Quick answer
Caffeine can interact with some medicines, and some medicines can change how long caffeine stays in the body. Caffeine is cleared mainly by one liver enzyme called CYP1A2, which handles about 95 percent of the caffeine a person takes in. [1] A medicine that slows that enzyme can leave caffeine active for longer, and caffeine in turn can affect how a few medicines are absorbed or handled. Reviews say caffeine "interacts with many medications," and MedlinePlus tells people who take stimulants, certain antibiotics, asthma medicines or heart medicines to check with a health care provider. [1][2]

This page explains what pharmacists look for. It is information, not advice about your own medicines. A pharmacist or prescriber who knows your full list can judge what matters for you. See also Medication Interactions.

How the evidence is labeled

Most caffeine interaction studies are small and were done in healthy volunteers over a few days. We label each finding: promising but limited (small studies that point one way), mixed (studies disagree), insufficient evidence (too little to judge), and case report (one person's experience, which cannot show how common a problem is). A change in caffeine blood levels is a lab measure, not proof that someone will feel unwell.

What the sources found

Medicine or situationWhat the source foundStrength of evidence
Ciprofloxacin (a fluoroquinolone antibiotic)In ten healthy men, caffeine half-life rose from about 5.2 to 8.2 hours during ciprofloxacin; the authors said the clinical significance remained to be determined. [3] A review found enoxacin and ciprofloxacin reduced caffeine clearance while ofloxacin did not. [4]Promising but limited (older volunteer studies)
Fluvoxamine (an antidepressant)In eight healthy volunteers, caffeine clearance fell from 107 to 21 ml per minute and half-life rose from 5 to 31 hours; the authors said caffeine intake during treatment may lead to caffeine intoxication. [5] In 30 patients with depression, fluvoxamine and caffeine blood levels were positively correlated. [6]Promising but limited
Clozapine (an antipsychotic)One reported patient on a stable clozapine regimen began drinking caffeinated energy drinks and developed life-threatening clozapine toxicity; the authors note caffeine is a known inhibitor of clozapine metabolism. [7]Case report
Estrogen-containing oral contraceptivesIn small studies, caffeine half-life was longer in users than in non-users (about 7.9 vs 5.4 hours in one, 10.7 vs 6.2 in another). [8][9]Promising but limited
Levothyroxine (thyroid hormone)A systematic review found limited evidence that coffee lowers levothyroxine absorption and suggested keeping a time gap. [10] The NHS says some foods can affect how levothyroxine works. [11]Limited; ask your pharmacist about timing
Statins after a heart eventA literature review found the only caffeine interaction in these patients was with a protective effect of statins on cardiac ischemia, and called these interactions less studied. [12]Insufficient evidence
Stimulants, asthma, heart medicinesMedlinePlus lists these groups as ones to check with a provider. [2] We did not find a source we could read that gives details for each.Proper evidence not found here

Other things that change caffeine in the body

Medicines are not the only factor. Smoking tends to speed caffeine breakdown, while pregnancy, oral contraceptives and various kinds of liver disease prolong its half-life. [13] Age, sex, hormones, obesity and diet also matter. [1] That is one reason the same cup of coffee feels different from person to person.

Caffeine you may not count

Caffeine can be an added ingredient in pain relievers, cold medicines and alertness products, as well as energy bars, gum and dietary supplements. [2][14] The FDA says the body handles added caffeine the same way as caffeine from coffee or tea, so all sources add up. [14] MedlinePlus also warns that combining alcohol and caffeine is dangerous. [2]

What we did not find

We searched PubMed for caffeine together with MAO inhibitors, lithium, theophylline and decongestants and did not find a source we could read and verify for this page, so we make no statement about them. That does not mean there is no interaction. It means this page is not a complete list. Official patient pages may not mention caffeine; the NHS ciprofloxacin page we read does not. [15] Ask the pharmacist rather than relying on a leaflet alone.

Who should ask first

  • Anyone taking a prescribed medicine long term, especially an antibiotic, an antidepressant, an antipsychotic, a thyroid medicine, a heart or asthma medicine, or the contraceptive pill. Tell the pharmacist about coffee, tea, energy drinks, caffeine pills and any supplement. [2][11]
  • People who are pregnant or breastfeeding. Pregnancy lengthens caffeine half-life. [13] See Caffeine in Pregnancy, Breastfeeding, Children and Teens.
  • People with liver disease, where caffeine stays longer. [13] We did not find a source on caffeine and kidney disease that we could read.
  • Anyone with a procedure planned. Pre-surgery caffeine advice is not described in the sources we read, so ask the surgical team, and do not change a prescribed medicine on your own.
  • Children, teens and people with anxiety, sleep problems, high blood pressure or heart rhythm problems, who MedlinePlus says should check about limiting caffeine. [2]

Signs of too much caffeine include a fast heartbeat, jitters, nausea and trouble sleeping. [14] If these appear after starting a new medicine, tell a clinician or pharmacist. For a large amount swallowed, see Caffeine Overdose and Toxicity.

Related pages

Caffeine: Supplements, Alertness and Limits · Caffeine and Energy Drinks · Nootropics and Medicine Interactions · Quality Testing and Certifications

Frequently asked questions

Does coffee stop antibiotics from working?

The sources we read did not test that question. They looked at the opposite direction for one antibiotic: ciprofloxacin slowed the body's clearance of caffeine in volunteers. [3] Ask a pharmacist about your specific antibiotic.

Can I drink coffee with thyroid medicine?

A systematic review found limited evidence that coffee reduces levothyroxine absorption, and the NHS notes foods can affect how it works. [10][11] Your pharmacist can explain the timing that fits your prescription.

Why does my antidepressant make caffeine feel stronger?

Fluvoxamine strongly slowed caffeine clearance in a small volunteer study. [5] Other antidepressants were not covered by the sources we read, so talk to your prescriber or pharmacist.

Are caffeine tablets or energy drinks riskier with medicines?

They can carry more caffeine in one go, and the one clozapine case involved energy drinks. [7][14] One case cannot show how common the problem is.

Is it safe to stop caffeine if I take regular medicines?

Do not change any prescribed medicine yourself. Stopping caffeine suddenly can bring headaches and drowsiness, [2] and the FDA says that cutting back gradually is best. [14] A pharmacist can say whether your medicines make that important.

References
  1. Nehlig A, Interindividual differences in caffeine metabolism and factors driving caffeine consumption. Pharmacol Rev 2018. Read 2026-10-23.
  2. MedlinePlus (US National Library of Medicine), Caffeine Read 2026-10-23.
  3. Healy DP et al., Interaction between oral ciprofloxacin and caffeine in normal volunteers. Antimicrob Agents Chemother 1989. Read 2026-10-23.
  4. Edwards DJ et al., Inhibition of drug metabolism by quinolone antibiotics. Clin Pharmacokinet 1988. Read 2026-10-23.
  5. Jeppesen U et al., A fluvoxamine-caffeine interaction study. Pharmacogenetics 1996. Read 2026-10-23.
  6. Yoshimura R et al., Interaction between fluvoxamine and cotinine or caffeine. Neuropsychobiology 2002. Read 2026-10-23.
  7. Yartsev A, Peisah C, Caffeine-clozapine interaction associated with severe toxicity and multiorgan system failure: a case report. BMC Psychiatry 2021. Read 2026-10-23.
  8. Abernethy DR, Todd EL, Impairment of caffeine clearance by chronic use of low-dose oestrogen-containing oral contraceptives. Eur J Clin Pharmacol 1985. Read 2026-10-23.
  9. Patwardhan RV et al., Impaired elimination of caffeine by oral contraceptive steroids. J Lab Clin Med 1980. Read 2026-10-23.
  10. Wiesner A et al., Levothyroxine interactions with food and dietary supplements: a systematic review. Pharmaceuticals 2021. Read 2026-10-23.
  11. NHS (UK), Levothyroxine (page last reviewed 6 July 2026) Read 2026-10-23.
  12. Yaghoobian R et al., Caffeine drug interactions and its clinical implication after acute coronary syndrome: a literature review. Crit Pathw Cardiol 2023. Read 2026-10-23.
  13. Kalow W, Variability of caffeine metabolism in humans. Arzneimittelforschung 1985. Read 2026-10-23.
  14. U.S. Food and Drug Administration (US), Spilling the Beans: How Much Caffeine is Too Much? (content current as of 08/28/2024) Read 2026-10-23.
  15. NHS (UK), Ciprofloxacin Read 2026-10-23.
Education, not medical advice. This page is for general information. It does not diagnose or treat any condition and is not a substitute for care from a qualified health professional. Natural does not automatically mean safe. Ask a clinician or pharmacist before changing your care, especially if you take medication, are pregnant or breastfeeding, or have a health condition.