Cannabis Adverse Effects, Cannabis Use Disorder and When to Seek Help

Urgent help first

• A child may have eaten cannabis or an edible. Take the child to a physician or emergency department, especially if the child acts in an unusual way or feels sick. [1] In the US, call 911 for severe symptoms and Poison Help at 1-800-222-1222. [2] See poisoning: what to do first and Poison Help by country.
• Crisis or thoughts of self-harm. In the US, call or text 988 to reach the 988 Suicide & Crisis Lifeline. [2]
• Wanting to cut down or stop. NIDA lists the SAMHSA National Helpline at 1-800-662-HELP (4357) for treatment referrals in the US. [2] See substance use support and urgent help.

Adverse Effects

This page describes harms found in research. It does not tell anyone how to use cannabis. Evidence labels: established, evidence of harm (an association seen in studies), mixed, and insufficient evidence.

Short-term effects. Cannabis can alter time perception and impair thinking, memory and body movement, and can make people irritable or restless. [2] Anxiety, fear, panic or hallucinations are more common when a large amount is taken, the product is strong, or the person has little experience. [2] NIDA also lists an elevated heart rate and respiratory problems, and says cannabis can raise heart rate and blood pressure right after use. [2]

Stronger products. Between 1995 and 2022, THC strength in illegal cannabis products seized by law enforcement quadrupled from 3.96% to 16.14%. [2]

Edibles. Edibles typically take longer to show effects, and NIDA warns that people may use more as a result, increasing the likelihood of serious negative health effects. [2] Among children under six reported to US poison centers, edible exposures rose from 207 cases in 2017 to 3,054 in 2021. 22.7% of all reported cases in 2017 to 2021 were admitted to hospital, and about 70% of cases with a known outcome had central nervous system depression. [3] Delta-8 THC products have also caused emergencies; see CBD products and labels. [4]

Long-term effects (evidence of harm, associations). Long-term cannabis smoking is associated with respiratory problems such as airway inflammation and chronic bronchitis. [2] Frequent or heavy use has been linked to problems with learning, memory, attention and processing speed. [2] NIDA says some research links long-term use with stroke, heart attack and arrhythmia, but more research is needed to know if the link is direct. [2]

Psychosis and mental health

Some evidence links cannabis use to earlier onset of psychosis in people with genetic risk factors, and intoxication can cause a temporary psychotic episode, especially at high doses. [2] A meta-analysis found the risk of psychosis rose with how often people used: significantly for weekly or more frequent use, with no significant risk for less frequent use. [5] These are observational studies, so they show association and not proof of cause. The BMJ umbrella review reported, with high certainty, that in the general population cannabis worsened positive psychotic symptoms. [6]

If you or someone you know has hallucinations, severe confusion or thoughts of self-harm after using cannabis, seek urgent care and use the contacts above.

Cannabinoid hyperemesis syndrome

Cannabinoid hyperemesis syndrome (CHS) is nausea, vomiting and abdominal pain after long-term, heavy cannabis use. [2] It can recur and often needs medical attention. [2] People sometimes try to relieve it temporarily with hot showers or baths, but NIDA says CHS only resolves when a person stops using cannabis completely. [2] NCCIH describes some long-term users of high doses developing recurrent severe vomiting. [7]

Cannabis Use Disorder

Cannabis use disorder is a type of substance use disorder. NIDA says studies estimate 22% to 30% of people who use cannabis have it, and that frequency of use is the strongest predictor. [2] The DSM-5 defines it as a pattern of use that leads to clinically significant impairment or distress, with two or more symptoms in 12 months. [2] Symptoms include using more or longer than intended, failed attempts to cut down, craving, and continuing despite problems at work, school or home. [2] Two or three symptoms is mild, four or five is moderate and six or more is severe. [2]

Signs to take seriously: trouble cutting down, giving up activities, using in risky situations, or needing more for the same effect. [2]

Withdrawal

Withdrawal can follow stopping or greatly reducing heavy or long-term use, even without a use disorder. [2] Symptoms may include irritability, anger, anxiety, restlessness, lower appetite or weight, depression, insomnia, strange dreams, headaches, sweating, abdominal pain and tremor. [2] A 2020 meta-analysis of 47 studies (23,518 people) estimated an overall prevalence of 47% among regular or dependent users, but 17% in population samples, 54% in outpatient and 87% in inpatient samples. [8] Another study cited by NIDA estimated 12.1% among frequent users. [2] Estimates vary widely depending on who is studied.

Treatment

NIDA says cognitive behavioral therapy, motivational enhancement therapy and contingency management can be effective for cannabis use disorder, and no FDA-approved medicines exist for it or for medically assisted withdrawal. [2] A 2025 Cochrane review of 37 trials agreed that medicines remain experimental. [9] A clinician or the helpline above can help with a plan.

Who is at higher risk

The BMJ umbrella review supports avoiding cannabis in adolescence and early adulthood, in people prone to or with mental health disorders, and in pregnancy. [6] NIDA notes cannabis may interact with warfarin, opioids and benzodiazepines in older adults. [2] See cannabis, pregnancy, teens and driving and medicine interactions.

Laws differ by country and change; this is not legal advice.