Marijuana May Not Be So Effective For Mental Health Issues, Study Finds

Forbes | Alice G. Walton

For people using cannabinoid medications to treat mental health issues, a new study may take the wind out of your sails. It finds that in general, the different versions of medicinal cannabis don’t have any clear therapeutic benefit for a range of disorders—in fact, the authors conclude, the risks may well outweigh the benefits. For anxiety, however, there may be some advantage; but even here, the quality of the evidence is low, making it unclear whether to put much stock in the association.

The meta-analysis, published in The Lancet Psychiatry, included 83 studies, half of which were randomized controlled trials, the gold-standard in research. Of the 83, 42 looked at depression, 31 at anxiety, 12 at post-traumatic stress disorder (PTSD), 11 at psychosis, eight at Tourette syndrome, and three at attention deficit/hyper activity disorder (ADHD). Different formulations were used in the various studies, including THC alone (THC is the psychoactive component of marijuana), THC with CBD (CBD inactive but purportedly more therapeutic compound), and more rarely, CBD alone.

There was some evidence that THC, either with or without CBD, was linked to reduced anxiety—but, they say, the quality of the evidence was low; that is, the quality of the studies was questionable. Additionally, THC was associated with an increased risk of adverse event (side effects) and withdrawal from the studies due to adverse events. Finally, there was “little evidence for the effectiveness of pharmaceutical CBD or medicinal cannabis for the treatment of any of these mental health disorders.”

They conclude that the benefits don’t likely outweigh the risks, given that there’s a larger body of evidence suggesting some concerning psychological risks of long term marijuana use. “There is scarce evidence to suggest that cannabinoids improve depressive disorders and symptoms, anxiety disorders, attention-deficit hyperactivity disorder, Tourette syndrome, post-traumatic stress disorder, or psychosis,” the authors, from the University of New South Wales, Australia, write in their paper.

It’s also important to think about how the compounds may affect mental health in the long term. Numerous studies have found that marijuana, especially high-potency varieties, increases the risk of psychosis in regular users, at least for those predisposed to it. And a study last year found that different formulations of medical marijuana had different effects on depression, anxiety, and stress. High CBD/low THC was best for reducing short-term depression, while low CBD/high THC was most effective for reducing stress; any type worked on anxiety. But the study also found that cannabis in general was linked to more significant symptoms of depression over the longer term, leading the authors to say, “continued use may exacerbate baseline symptoms of depression over time.”

More work will be needed to really understand the effects of cannabis in all its iterations both in the short and long runs. It’s important to remember that this area of work is still evolving and a lack of results can just mean that there aren’t enough well-designed studies to draw conclusions. But it’s also important to be skeptical of any medication that promises to be an amazing fix for mental health disorders, especially in isolation from other perhaps more-effective strategies.


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