Cannabis can help mental health and harm it. The result depends on THC dose, CBD ratio, age at first use, family history of psychosis, and how often a person uses. Evidence for harm is strongest at high THC doses and with daily use. Evidence for benefit is strongest for CBD in a small number of conditions.
What the evidence supports
- CBD for two epilepsy syndromes. The FDA approved Epidiolex, a purified CBD oral solution, for seizures tied to Lennox-Gastaut and Dravet syndromes in patients age 1 and older.
- CBD for anxiety. Small trials report lower anxiety at doses of 300 mg to 600 mg before public speaking and in social anxiety settings. Results across studies differ.
- THC for sleep onset. THC can shorten the time to fall asleep. Tolerance builds in days to weeks, and sleep can worsen after stopping.
- THC for nausea and appetite. Dronabinol, a synthetic THC, is FDA approved for chemotherapy-induced nausea and for weight loss in AIDS patients.
What the evidence warns about
- Psychosis. A 2019 study in Lancet Psychiatry across 11 sites found daily use of high-potency cannabis (THC above 10%) linked to about 3 to 5 times higher odds of a psychotic disorder. Confounding remains. A family history of psychosis raises risk more than cannabis alone.
- Anxiety and paranoia. THC at high doses can trigger panic, a fast heart rate, and paranoia. Inhaled effects last 1 to 3 hours. Edible effects can last 6 hours or longer.
- Depression and suicidal thoughts. Observational studies link heavy use to depression and suicide risk. The direction of cause is unclear. People with depression may use cannabis to self-treat.
- Cannabis use disorder. NIDA reports about 3 in 10 users develop some level of dependence. Withdrawal includes irritability, insomnia, appetite loss, and cravings. Symptoms peak in the first week and ease over 1 to 2 weeks.
- Teen use. Starting before age 18 is tied to higher risk. The endocannabinoid system is still developing in the teen brain.
What is unknown
Few long-term randomized trials exist. Most data is observational, so reverse causation is possible. CBD dosing standards are lacking for anxiety and sleep. Label accuracy for retail products varies by state testing rules. Long-term effects of concentrates above 60% THC are not well studied.
Steps to lower risk
- Start with low THC. Products above 10% THC carry more risk than flower from the 1990s, which averaged about 4% THC.
- Check the CBD to THC ratio. Higher CBD may offset some THC effects. Evidence on this point is thin.
- Limit frequency. Use once a week or less, not every day.
- Skip cannabis with a personal or family history of psychosis, schizophrenia, or bipolar disorder.
- Check drug interactions. CBD inhibits the CYP3A4 and CYP2C19 enzymes. This can raise blood levels of warfarin, clobazam, and some antidepressants. Ask a pharmacist.
- Buy from licensed shops and ask for a certificate of analysis.
Bottom line
Cannabis is not one drug. A 5 mg THC edible, a 25% THC vape, and a 600 mg CBD capsule act in different ways. People with a psychosis risk profile face the largest known harm. People seeking CBD for seizures have the clearest evidence of benefit. Anyone with a mental health diagnosis should tell their prescriber about cannabis use.