Medical Cannabis Clinical Research: What Trials Show

Answer first

Clinical research on medical cannabis rests on a small set of randomized controlled trials. Most test purified cannabinoids, not smoked flower. The FDA has approved three cannabis-related drugs: Epidiolex (cannabidiol) for Dravet syndrome, Lennox-Gastaut syndrome and tuberous sclerosis complex, plus dronabinol and nabilone, both synthetic THC, for chemotherapy-induced nausea and vomiting. No smoked or vaporized cannabis product holds FDA approval.

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Where the evidence is strongest

Chronic pain

A 2015 meta-analysis in JAMA by Whiting and colleagues pooled 79 trials with 6,462 participants. It found moderate-quality evidence that cannabinoids reduce chronic pain. A 2018 Cochrane review of neuropathic pain covered 16 studies with about 1,750 people and rated the evidence low quality. Both reviews note small samples and short follow-up.

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Multiple sclerosis spasticity

Oromucosal nabiximols (Sativex), a THC and CBD spray, is approved for MS spasticity in Canada, the UK and several European countries. It is not approved in the United States. Trials show a modest drop in spasticity scores, with results that vary by study.

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Chemotherapy nausea

Dronabinol (Marinol) received FDA approval in 1985 for nausea and vomiting in patients who fail standard antiemetics. It gained a second approval in 1992 for appetite loss in AIDS. Nabilone (Cesamet) was approved in 1985 for the same nausea use.

Epilepsy

Epidiolex won FDA approval in 2018 after three pivotal trials. Two enrolled about 171 and 225 patients with Lennox-Gastaut syndrome. One enrolled about 120 patients with Dravet syndrome. The trials measured median reduction in monthly seizure frequency against placebo. Approval for tuberous sclerosis complex followed in 2020.

How US research is regulated

Cannabis sits in Schedule I of the Controlled Substances Act. A study needs DEA registration, an FDA investigational new drug application and institutional review board approval. For decades the only legal supply came from the NIDA Drug Supply Program at the University of Mississippi. The DEA has moved to register additional growers since 2021.

In August 2023 the Department of Health and Human Services recommended moving cannabis to Schedule III. The DEA has not issued a final rule. Most states allow medical cannabis, but state law does not change federal trial requirements.

Design problems

• Blinding. THC causes psychoactive effects, so participants can guess their assignment.

• Product variance. THC and CBD content shifts by batch, strain and growing method.

• Delivery. Smoking and vaping give variable doses and add combustion byproducts.

• Size. Most trials run under 12 weeks with fewer than 200 participants.

• Funding. Industry sponsors run many trials, which raises bias questions.

Open questions

Long-term safety. Psychosis risk in heavy users with a family history. Heart and blood pressure effects. Cannabis use disorder. Effects on adolescent brains. Whether whole-plant preparations beat purified cannabinoids. Dose standards. Driving impairment.

Where to check current work

ClinicalTrials.gov lists registered studies with phase and enrollment status. PubMed and the Cochrane Library hold peer-reviewed results and systematic reviews. The 2017 National Academies report remains the broadest US review. It found conclusive evidence for chronic pain, chemotherapy-induced nausea and MS spasticity, and limited or no evidence for most other conditions.