In 2017, a National Academies of Sciences, Engineering, and Medicine (NASEM) report comprehensively evaluated the body of evidence regarding cannabis health effects through the year 2016. The objectives of this study are to identify and map the most recently (2016–2019) published literature across approved conditions for medical cannabis and to evaluate the quality of identified recent systematic reviews, published following the NASEM report. Following the literature search from 5 databases and consultation with experts, 11 conditions were identified for evidence compilation and evaluation: amyotrophic lateral sclerosis, autism, cancer, chronic noncancer pain, Crohn’s disease, epilepsy, glaucoma, human immunodeficiency virus/AIDS, multiple sclerosis (MS), Parkinson’s disease, and posttraumatic stress disorder. A total of 198 studies were included after screening for condition-specific relevance and after imposing the following exclusion criteria: preclinical focus, non-English language, abstracts only, editorials/commentary, case studies/series, and non-U.S. study setting. Data extracted from studies included: study design type, outcome definition, intervention definition, sample size, study setting, and reported effect size. Few completed randomized controlled trials (RCTs) were identified. Studies classified as systematic reviews were graded using the Assessing the Methodological Quality of Systematic Reviews-2 tool to evaluate the quality of evidence. Few high-quality systematic reviews were available for most conditions, with the exceptions of MS (9 of 9 graded moderate/high quality; evidence for 2/9 indicating cannabis improved outcomes; evidence for 7/9 indicating cannabis inconclusive), epilepsy (3 of 4 graded moderate/high quality; 3 indicating cannabis improved outcomes; 1 indicating cannabis inconclusive), and chronic noncancer pain (12 of 13 graded moderate/high quality; evidence for 7/13 indicating cannabis improved outcomes; evidence from 6/7 indicating cannabis inconclusive). Among RCTs, we identified few studies of substantial rigor and quality to contribute to the evidence base. However, there are some conditions for which significant evidence suggests that select dosage forms and routes of administration likely have favorable risk-benefit ratios (i.e., epilepsy and chronic noncancer pain). The body of evidence for medical cannabis requires more rigorous evaluation before consideration as a treatment option for many conditions, and evidence necessary to inform policy and treatment guidelines is currently insufficient for many conditions.

Background: Medical cannabis is available to patients by physician order in two-thirds of the United States (U.S.) as of 2020, but remains classified as an illicit substance by federal law. States that permit medical cannabis ordered by a physician typically require a diagnosed medical condition that is considered qualifying by respective state law. Objectives: To identify and map the most recently (2016-2019) published clinical and scientific literature across approved conditions for medical cannabis, and to evaluate the quality of identified recent systematic reviews. Methods: Literature search was conducted from five databases (PubMed, Embase, Web of Science, Cochrane, and ClinicalTrials.gov), with expansion and update from the National Academies of Sciences, Engineering, and Medicine’s (NASEM) comprehensive evidence review through 2016 of the health effects of cannabis on several conditions. Following consultation with experts and stakeholders, 11 conditions were identified for evidence evaluation: amyotrophic lateral sclerosis (ALS), autism, cancer, chronic pain, Crohn’s disease, epilepsy, glaucoma, HIV/AIDS, multiple sclerosis (MS), Parkinson’s disease, and posttraumatic stress disorder (PTSD). The following exclusion criteria were imposed: preclinical focus, non-English language, abstracts only, editorials/commentary, case studies/series, and non-U.S. study setting. Data extracted from studies included: study design type, outcome, intervention, sample size, study setting, and reported effect size. Studies classified as systematic reviews with or without meta-analysis were graded using the AMSTAR-2 tool by two raters to evaluate the quality of evidence, with additional raters to resolve cases of evidence grade disagreement. Results: A total of 438 studies were included after screening. Five completed randomized controlled trials (RCTs) were identified, and an additional 11 trials were ongoing, and 1 terminated. Cancer, chronic pain, and epilepsy were the most researched topic areas, representing more than two-thirds of all reviewed studies. The quality of evidence assessment for each condition suggests that few high-quality systematic reviews are available for most conditions, with the exceptions of MS, epilepsy, and chronic pain. In those areas, findings on chronic pain are mostly in alignment with the previous literature, suggesting that cannabis or cannabinoids are potentially beneficial in treating chronic neuropathic pain. In epilepsy, findings suggest that cannabidiol is potentially effective in reducing seizures in pediatric patients with drug-resistant Dravet and Lennox-Gastaut syndromes. In MS, recent high-quality systematic reviews did not include new RCTs, and are therefore not substantially expanding the evidence base. In sum, the most recent clinical evidence suggests that for most of the conditions assessed, we identified few studies of substantial rigor and quality to contribute to the evidence base. However, there are some conditions for which significant evidence suggests that select dosage forms and routes of administration likely have favorable risk-benefit ratios (i.e., epilepsy and chronic pain), with the higher quality of evidence for epilepsy driven by FDA-approved formulations for cannabis-based seizure treatments. Conclusion: The body of evidence for medical cannabis requires more rigorous evaluation before consideration as a treatment option for many conditions and evidence necessary to inform policy and treatment guidelines is currently insufficient for many conditions.