For every study that gives weight to marijuana’s medicinal benefits, there’s another claiming medical marijuana is not only ineffective but a danger to anyone who uses it for the treatment of certain conditions, including cancer, HIV/AIDS, multiple sclerosis, epilepsy, anxiety, and depression. A recent study conducted by Dr. Penny F. Whiting and his colleagues from the University of Bristol in the United Kingdom highlighted the mixed findings associated with use of cannabinoids for medical purposes.

Medical marijuana has been legalized in 23 states and the District of Columbia with multiple states currently mulling over potential legalization laws. With nearly half of the United States falling in line with the use of cannabinoids as medical therapy, one would think the benefits and drawbacks of pot are more unambiguous than they actually are. This begs the question: Why is it so hard to prove that medical marijuana is either good or bad?

"Further large, robust, randomized clinical trials are needed to confirm the effects of cannabinoids, particularly on weight gain in patients with HIV/AIDS, depression, sleep disorders, anxiety disorders, psychosis, glaucoma, and Tourette syndrome are required,” the authors said in a statement. “Further studies evaluating cannabis itself are also required because there is very little evidence on the effects and AEs of cannabis.”

The research team analyzed 79 randomized clinical trials, which included 6,462 participants, exploring both the benefits and adverse events related to medical marijuana. Although most trials found that cannabinoids improved certain symptoms, the numbers showed dissimilarities in these findings. For example, the evidence supporting medical marijuana’s beneficial effect on symptoms for cancer and multiple sclerosis was considered moderate-quality. On the other hand, the evidence supporting medical marijuana’s beneficial effect on chemotherapy-induced vomiting, weight gain related to HIV, sleep disorders, Tourette syndrome, and anxiety was consider low- or very low-quality.

"If the states' initiative to legalize medical marijuana is merely a veiled step toward allowing access to recreational marijuana, then the medical community should be left out of the process, and instead marijuana should be decriminalized," Dr. Deepak Cyril D'Souza and Dr. Mohini Ranganathan from the Yale University School of Medicine said in an accompanying editorial.

Researchers from the University of Bristol also found an increased risk for adverse events associated with medical marijuana use, such as dizziness, dry mouth, nausea, fatigue, somnolence, euphoria, vomiting, disorientation, drowsiness, confusion, loss of balance, and hallucination.

"Conversely, if the goal is to make marijuana available for medical purposes, then it is unclear why the approval process should be different from that used for other medications,” D’Souza and Ranganathan explained. “Evidence justifying marijuana use for various medical conditions will require the conduct of adequately powered, double-blind, randomized, placebo/active controlled clinical trials to test its short- and long-term efficacy and safety.”

So why is it so hard to study medical marijuana? Well, to put it mildly, because the government makes it hard. Any researcher looking to study the effects of cannabinoids have only one option to turn to: the Marijuana Research Project at Ole Miss. In fact, the university and the Drug Enforcement Administration (DEA) have held the monopoly on medical marijuana for more than 45 years. Unfortunately, it looks like this monopoly may last a lot longer after the National Institutes of Health awarded the University of Mississippi $68.8 million to continue growing federally legal pot.

“The federal government and states should support medical marijuana research,” D’Souza and Ranganathan added. “Since medical marijuana is not a life-saving intervention, it may be prudent to wait before widely adopting its use until high-quality evidence is available to guide the development of a rational approval process."

Source: Wolff R, Deshpande S, Whiting P, et al. Cannabinoids for Medical Use: A Systematic Review and Meta-analysis. JAMA. 2015.