Cannabis and Cannabinoid Clinical Research: What Systematic Reviews Show

Clinical Studies: the big picture

Clinical research means studies in people. The strongest summaries are systematic reviews, which search for all trials on a question and combine them. Reviews in this field keep reaching a similar overall picture: a few clear benefits for specific conditions, small effects for others, little evidence for many popular uses, and a steady list of side effects.

Evidence labels used on this page: approved medicine (a regulator reviewed trials for a stated use), established, promising but limited, mixed, insufficient evidence, no good evidence of benefit, and evidence of harm.

The main reviews

• JAMA, 2015. A review of 79 trials with 6,462 participants found only 4 at low risk of bias. It rated the evidence moderate-quality for chronic pain and spasticity and low-quality for chemotherapy nausea, HIV weight gain and sleep disorders. Short-term side effects were more common with cannabinoids. [1]
• BMC Medicine, 2022. A review of 152 randomized trials (12,123 participants), organized by product, found a significant effect of CBD for epilepsy and moderate evidence for dronabinol and nabiximols in some uses. All other significant effects had low, very low or no grade of evidence. [2]
• BMJ umbrella review, 2023. It examined 101 meta-analyses. It found that cannabidiol is effective in people with epilepsy and that cannabis-based medicines are effective in people with multiple sclerosis, chronic pain, inflammatory bowel disease and in palliative medicine, but not without adverse events. [3]

These reviews counted products differently. The BMC review looked only at trials of four named products: dronabinol, nabilone, cannabidiol and nabiximols. [2] That matters, because most people asking about "medical cannabis" are thinking of a store product, and a trial of a drug does not tell you about a store product.

By condition

Why the answers are not clean

• Short studies. Trials in the BMJ pain review followed patients for 1 to 5.5 months, so long-term effects are unknown. [7]
• Mixed quality. Only 4 of 79 trials in the JAMA review were at low risk of bias. [1]
• Different products. The effect of a purified CBD drug, a THC drug and a mouth spray with both can differ, and the BMC reviewers suggested future reviews be based on each product's specific pharmacology. [2]
• Dated reviews. NCCIH's summary was last updated in November 2019, so it does not include newer trials. [6]

Side effects across the research

Short-term adverse events were more common with cannabinoids in the JAMA review, which listed dizziness, dry mouth, nausea, fatigue, somnolence, euphoria and confusion among the common ones. [1] In the BMJ pain review, oral medical cannabis probably caused a small increase in transient cognitive impairment, and dizziness was more frequent. [7] The umbrella review concluded that avoiding cannabis is supported during adolescence and early adulthood, in people prone to or with mental health disorders, and in pregnancy. [3]

Read more at cannabis adverse effects and use disorder and approved cannabinoid medicines.

What this does not tell you

These findings are not advice to start or stop treatment. FDA says it has not approved cannabis for any disease or condition, and it warns that unapproved products have not been evaluated for dosage or interactions. [5] Discuss any use with a clinician; see talking with a health professional. Laws differ by country; see cannabis laws by country.