Long term medical cannabis use carries documented risks. The main ones are cannabis use disorder, memory and attention changes, airway symptoms from inhaled products, cannabinoid hyperemesis syndrome, and liver enzyme changes from cannabidiol. Heart and mental health risks appear in a smaller share of users. Evidence quality differs by outcome, and several areas have no long term data.
medical cannabis vs recreational weed differences
What counts as long term
Trials of FDA-approved cannabinoid medicines run 3 to 14 weeks. Observational studies follow people for 1 to 30 years. Most long term data comes from people who used cannabis for years before any medical use. Patients who start under clinical supervision have less follow-up data.
Best Medical Strains for Anxiety and Depression: A Convenience-First Comparison
Regulated cannabinoid medicines
Epidiolex (cannabidiol)
In trials lasting 3 to 4 months, adverse reactions reported in 10% or more of patients included diarrhea, sleepiness, decreased appetite, fatigue, fever, vomiting, and elevated liver enzymes. Liver monitoring is part of the label.
medical cannabis for chronic pain patients
Dronabinol and nabilone
Both are synthetic THC. Labels list drowsiness, dizziness, and impaired coordination. Dronabinol is approved for nausea and appetite loss in chemotherapy and AIDS patients.
how to get a medical cannabis card online
Cannabis use disorder
CDC and NIDA report about 3 in 10 people who use cannabis develop cannabis use disorder. Risk is higher for people who start before age 18. Signs include use despite problems at work or home, tolerance, withdrawal, and failed attempts to cut back.
Cognitive effects
Studies of heavy users show small effects on memory and attention during periods of use. Effects on IQ in adults are small and can fade after about 1 month of abstinence. Adolescent onset is linked to larger effects. Causality is not settled.
Breathing and lungs
Smoked cannabis produces tar, carbon monoxide, and irritants. Regular smoking is linked to chronic bronchitis, cough, and phlegm. Evidence on COPD and lung cancer is mixed. Vaping avoids combustion but carries its own risks.
Cannabinoid hyperemesis syndrome
CHS causes repeated vomiting, abdominal pain, and nausea. Symptoms often improve with hot showers. Episodes appear after years of regular use. Stopping cannabis ends the episodes in most cases. Prevalence in medical users is unknown.
Mental health
High-THC products and early use are linked to a higher risk of psychosis in people with genetic risk. A causal link is debated. Reviews note a dose-response pattern. Screening for personal or family history of psychosis matters before starting.
Heart and blood vessels
Cannabis raises heart rate for up to 3 hours after use. Case reports link use to heart attack and stroke. Observational studies show a small rise in risk. People with existing heart disease face the largest concern.
Interactions and monitoring
- CBD inhibits CYP2C19 and CYP3A4. Levels of clobazam, warfarin, tacrolimus, and some anticonvulsants can rise.
- Sedatives and opioids add to drowsiness and slow breathing.
- Liver tests are advised for CBD-dominant products.
- No safe amount in pregnancy has been established.
What is not known
Data on high-THC concentrates is thin. Data on users over 65 is thin. State programs track few outcomes, so long term safety data on medical products sold at dispensaries is limited.
When to talk to a clinician
Get help for repeated vomiting, chest pain, fainting, new psychotic symptoms, or an inability to cut back. Withdrawal peaks in the first week and includes irritability, sleep problems, and craving.