The White House has just announced that it will be relaxing some of its strict regulations on marijuana research, making it easier for scientists to conduct clinical studies on the drug. This could not have come at a better time, it seems, as a comprehensive review of 40 years of human trials that examined its potential use in treating a variety of ailments has suggested that high-quality evidence supporting its therapeutic use is lacking.

Interest in the use of marijuana in the treatment of various medical conditions has grown over the last few decades, with numerous clinical trials suggesting that it could serve as a useful addition to the arsenal of therapies already available for some health problems, including pain, chemotherapy-induced nausea and appetite loss. Although marijuana has not been FDA-approved as an effective treatment for anything, the agency has considered the available evidence and instead approved synthetic versions of an active compound, or cannabinoid, found in the plant.

More than 20 states have now legalized the use of medical marijuana for a range of conditions, and a further seven are still considering legislation. With its increasing popularity, now is the time to critically evaluate its effectiveness in clinical settings, which is precisely what a team of researchers from the University of Bristol recently set out to do.

As described in the journal JAMA, the team set out to review the benefits of cannabinoids in the treatment of various diseases or symptoms. Almost 80 randomized clinical trials were included in the study, which revealed that the majority found an improvement in symptoms with the use of cannabinoids. While this may sound positive, they actually found that most of these associated health improvements were not statistically significant.

Importantly, many studies were found to be poorly designed, for example including only a small number of participants or continuing despite a high dropout rate, leading to issues with the reliability of the data. Of those that were considered to be of moderate quality, support was found for the use of cannabinoids in the treatment of chronic pain and spasticity due to multiple sclerosis. But for sleep disorders, weight gain in HIV infection, Tourette's syndrome, and nausea due to chemotherapy, studies reporting improvements with cannabinoid use were considered to be of low quality.

So if the studies aren’t good enough, why is medical marijuana so widely used to treat certain diseases? The FDA actually requires a minimum of two randomized clinical trials of adequate quality before a drug can be approved for a specific medical condition, but it seems that many cannabis studies have slipped through the net. But as pointed out by an accompanying editorial, this arguably reflects difficulties in conducting clinical studies on the drug due to its classification as a Schedule 1 drug.

The take-home message from this review is therefore not that marijuana has no place in modern medicine, but that there is a clear need for more robust studies into its use, especially given the fact that more governments are now contemplating its legalization as a medicinal or recreational drug. 

[Via JAMA, JAMA and New Scientist]