A Systematic Review of the Evidence for Medical Marijuana in Psychiatric Indications

Objective: Marijuana has been approved for a number of psychiatric conditions in many states in the US including posttraumatic stress disorder (PTSD), agitation in Alzheimer's disease, and Tourette's disorder. In this systematic review, we examine the strength of evidence for the efficacy of marijuana and other cannabinoids for these psychiatric indications.

Data sources: The literature (MEDLINE) was searched for studies published between January 1980 and March 2015 using search terms related to marijuana and other cannabinoids and the specific diagnosis.

Study selection: The best quality of evidence, namely placebo-controlled, randomized clinical trials (RCTs) and meta-analyses, was sought per PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. In the absence of RCTs, the next best available evidence (eg, observational studies, case reports) was reviewed. Of 170 publications that were screened, 40 were related to the topic, 29 were included in the qualitative synthesis, and 13 studies examined the efficacy of cannabinoids in humans.

Data extraction: The evidence was rated using the GRADE (Grading of Recommendations, Assessment, Development, and Evaluation) method.

Results: No RCTs have thus far examined the efficacy of marijuana for Tourette's disorder, PTSD, or Alzheimer's disease. Lower-quality studies examined the efficacy of marijuana, Δ⁹-tetrahydrocannabinol, and nabilone; the strength of evidence for the use of cannabinoids for these conditions is very low at the present time. The consequences of chronic cannabinoid exposure includes tolerance, dependence, and withdrawal. Early and persistent marijuana use has been associated with the emergence of psychosis. Marijuana impairs attention, memory, IQ, and driving ability.

Conclusions: Given its rapidly changing legal status, there is an urgent need to conduct double-blind, randomized, placebo- or active-controlled studies on the efficacy and safety of marijuana or its constituent cannabinoids for psychiatric conditions. Physicians and policy-makers should take into account the limited existing evidence and balance that with side effects before approving medical marijuana for psychiatric indications.