There Is Almost No Evidence That Cannabis Will Improve Mental Health Conditions
Disorders of negative affect, such as depression and anxiety, are among the most common psychiatric illnesses in the United States. According to the Anxiety and Depression Association of America, 40 million adults are affected by anxiety disorders. Not surprisingly, anti-depressants are some of the most frequently prescribed medications in the US. While these drugs undoubtedly help many manage their conditions, they are not without side effects, and often lose efficacy over time, leading the depressed and anxious to turn to other sources of relief.
Increasingly, this takes the form of medical marijuana. A 2016 survey revealed that 58% of medical cannabis consumers in Washington state did so for anxiety relief. Similar numbers were obtained for those seeking to ease their depression. In a separate survey, 12.7% of respondents said they were using cannabis in place of their prescription anti-depressants. Clearly, there is a demand for alternatives, and a belief that marijuana can help.
Unfortunately, there is very little research to suggest that cannabis is effective for this purpose. In fact, there’s a troubling paucity of trustworthy clinical research on this subject, as demonstrated by a new study published in The Lancet Psychiatry. In this paper, the authors examine the evidence showing either a positive or negative effect of cannabis on six different mental disorders. What they found shows just how far we still have to go in investigating the potential of medical marijuana.
What Did They Do?
Rather than perform new research on this subject, the authors of this paper used a technique called meta-analysis. The strength of any scientific finding comes from repeated measurements and replication by multiple research groups. The goal of a meta-analysis, then, is to synthesize every piece of research in an attempt to generate a consensus. However, this goes beyond simply reading a bunch of papers to see if the results are similar or not. Meta-analysis uses statistical methods to directly combine the results from each paper and treat them all as a single result. When done correctly, the conclusions drawn from meta-analyses are stronger than those from any single study alone.
Citing the increasing popularity of cannabis use for mental disorders, the authors chose six conditions to focus on: Depression, Anxiety, ADHD, Tourette Syndrome, PTSD, and Psychosis. Then they scoured databases of scientific literature searching for any papers mentioning cannabis and any one of these conditions. From there, they filtered out their results based on pre-determined criteria, keeping only the most relevant pieces of evidence. In particular, they focused on Randomized Controlled Trials (RCTs), the so-called “gold standard” in medical research. Using their systematic approach, the authors were able to filter through thousands of research articles and narrow their focus to a much more manageable eighty-three.
The final step in the process was to evaluate each of the remaining papers and grade the strength of the evidence. Under their scheme, an RCT is initially rated as “high quality”, and then downgraded to “moderate”, “low”, or “very low” as befit the situation. With all of their data collected and graded, they grouped the papers together based on the condition being studied and analyzed the results.
What Did They Find?
Unfortunately, after all that work collecting, evaluating, and synthesizing the best available clinical research, they found very few positive results. I should point out that “positive” in this case only means “proof of effect”, and not that the results are “good”. For Depression, ADHD, and Tourette Syndrome, there was no evidence that cannabinoids had any effect whatsoever. However, the evidence for these conclusions were all rated either “low” or “very low” due to methodological flaws. The other results are summarized below:
A combination of pharmaceutical grade THC and CBD was found to alleviate symptoms of anxiety better than a placebo. However, the size of effect was quite small, and the evidence is graded as “very low quality”. This is because none of the studies used for this analysis were examining anxiety directly. Rather, these were studies done on patients with chronic conditions that happened to keep track of anxiety symptoms. There was also a lot of inconsistency across studies, and some did such a poor job of reporting their results that they had to be thrown out of the analysis.
There was slightly better evidence for studying CBD on its own. A pair of RCTs studied the effect of pharmaceutical grade CBD on those with social anxiety, and found that it had no effect when compared to placebo.
Post-Traumatic Stress Disorder
The authors found only one RCT looking at the effect of cannabinoids on PTSD. While there was no evidence that THC-CBD could lessen the intensity of episodes or make them go away, it did show a reduction in nightmares and “improved global functioning”. Unfortunately, this evidence was graded “low” due to inconsistent, imprecise results.
To understand these results, we first need a little context. The symptoms of psychosis are separated into two types, Positive and Negative. In this case, Positive refers to abnormal symptoms that occur as part of the disease. This includes hallucinations, delusions, and scattered thinking. Negative symptoms are normal behaviors that are absent due to disease, such as a lack of pleasure, reduced motivation, or reduced spontaneous speech.
One RCT investigated the use of a combination of THC-CBD to treat psychosis. There was no change in the Positive symptoms (compared to placebo), but a significant worsening of the Negative symptoms. Further, the researchers found a strong negative effect on cognitive functioning after cannabinoid treatment. CBD on its own did not effect either the Positive or Negative symptoms, but it did significantly improve “global functioning”.
Adverse Events/Study Withdrawals
The authors also looked at whether or not those taking cannabinoids were more likely to suffer from side effects. Taking THC led to significantly more side effects and to more people dropping out of studies than placebo. However, when compared to other active drugs, there was no measurable difference. Further, this evidence was graded “low to moderate”, as most of the participants in these studies did not have mental disorders.
What Does This Mean?
The biggest takeaway from all of this is just how little we know when it comes to using cannabinoids to treat mental health disorders. To quote the authors:
“To our knowledge, this is the most comprehensive systematic review and meta-analysis examining the available evidence for medicinal cannabinoids in treating mental disorders and symptoms. There is a notable absence of high-quality evidence where mental disorders are the primary target of treatment[…]”
To put it another way, there is almost no evidence that cannabinoids can treat mental health disorders. Now, this does not mean that cannabis can’t treat them. Absence of evidence is not evidence of absence. But given that so many are turning to cannabis and cannabinoids for mental health reasons, we need to understand this much better, and sooner rather than later.
Highlighting this gap in our knowledge is important for several reasons. First, it’s possible that people are putting themselves at risk with little or no chance of reward. Every drug comes with side effects. Often these are negligible, or at the very least they are worth suffering in order to make the original issue go away. But in the case of cannabis and mental disorders, there’s evidence for negative side effects with little or no benefit. Further, cannabis can exacerbate certain conditions, as we saw with the patients with psychosis. This paper demonstrates how little we actually know, and might help sway some people to choose a different path.
This lack of knowledge also impacts policy decisions. Without federal legalization, each state is left to choose which conditions qualify a patient for medical marijuana. As of now, 29 states allow doctors to authorize medical marijuana use for the treatment of PTSD, 8 for the treatment of Tourette, and only 1 for anxiety. Clearly, these decisions were not made based on the strength of the science. It’s impossible to know what harm, if any, will come as a result of these decisions… but that’s exactly my point. We are acting blindly on this issue.
Finally, it arms people against dubious claims. Illegality leads to a lack of regulation. As it stands, there is very little oversight as to what claims can be made in advertising and selling marijuana. Therefore, it’s on the consumer to be educated and understand the risks and rewards before trying a new drug. By making it clear just how little we truly know, consumers can more effectively gauge the messages their receiving and make informed decisions.
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About the author:
J. Brandon Lowry holds a PhD from the Institute of Molecular Biology at the University of Oregon. A digital nomad and freelance writer, he writes about cannabis, science, health, and travel. He is also editor at Midnight Mosaic Fiction.