Many People with Bipolar Disorder Use Cannabis. It May Sometimes Help

People with bipolar disorder may continue to smoke cannabis, despite all the negative effects.

Credit: Michael M. Santiago/Getty imagesMany people suffering from bipolar disorder are attracted to marijuana. A 2019 review of 53 studies found that almost a quarter of a combined sample of 51,756 individuals with the condition used cannabis or had a problematic pattern of consumption (cannabis use disorder), compared with 2 to 7 percent in the general population—and an earlier study placed usage estimates still higher.

Cannabis and bipolar disorder don’t mix well. There may be an increase in manic and paranoid symptoms due to cannabis consumption, as well as a higher risk of suicide. Is it possible to explain the allure of cannabis as a form of substance misuse? Is it possible that bipolar disorder sufferers are attracted to cannabis? Is there any benefit to them?

Alannah Miranda of University of California San Diego is a postdoctoral researcher working with U.C.S.D. These questions were explored by William Perry, a psychiatrist professor, and Arpi Minassian, psychiatry professors. Miranda presented her and her colleagues’ unpublished work at this year’s giant Society for Neuroscience conference, which attracted more than 24,000 people earlier this month. She Scientific American interviewed her about the findings of this ongoing study, which was funded by The National Institute on Drug Abuse.

[An edited transcript of the interview follows.]

Tell me about what you’re studying.

I’m researching the effects of cannabis on cognition in people with bipolar disorder. People with bipolar disorder report that it’s helping alleviate some of their symptoms in terms of issues related to memory, attention, focus and anxiety.

What did the preliminary study that you’re presenting at this conference show?

There were four groups in our study: healthy participants without cannabis use, healthy participants with cannabis use, bipolar disorder sufferers who don’t use cannabis, and bipolar patients who do.

We evaluated their goal-directed behavior. They were tested on their willingness to accept a challenge despite decreasing reward potential. We found that bipolar patients who use cannabis make fewer risky choices and are less likely to take on trivial tasks over a long period of time. The risk-taking and effortful motivation levels of those who had not ingested cannabis were higher in people with bipolar disorder.

What number of people participated in the study?

So far, there have been 60 participants. The study is continuing, and we’re aiming for about 100 in total. And we’ll finish it in less than a year.

Previous studies have shown that cannabis can be used to treat bipolar disorder. What is the difference between your study and others?

The main focus of cannabis use to treat bipolar disorder has been on how the drug affects mood symptoms. This could make mania and psychosis more severe. However, impaired cognition like decision-making and memory loss is often overlooked. So we’re looking at these cognitive functions that are really impacting people’s everyday functioning.

Do you also do animal studies?

Yes, I’ve been collaborating with Jared Young at U.C.S.D. On his animal work. Our study is different from many other studies on bipolar and cannabis. We are not only looking at it in humans but also in animals. The paradigm is to test cognitive functions in humans, but we have very similar tasks that we’re using in mice. And we can do some genetic manipulations in mice or administer specific levels of drugs in the animals that we can’t do in humans. We can examine the mechanism of bipolar disorder we believe to exist. This could include a dysregulation in the signaling molecule, dopamine. It’s much more difficult to look at specific proteins in humans, but we can certainly do that in our animal research.

Do you have hypotheses about what might be going on with cannabis and how it’s affecting the brain?

We believe that cannabis could be affecting motivation and reward processing. Dopamine controls our behavior and how we use it to reach certain goals. Bipolar disorder may have excessive dopamine activity, which can lead to cognitive impairment.

So we think that cannabis may be reducing the excess dopamine in people with bipolar disorder that’s leading to cognitive impairment.

Could you talk about your work’s implications for possible treatments?

There would be concern that cannabis could make bipolar disorder symptoms worse. So I wouldn’t go so far as to say people with bipolar disorder should use cannabis. Our research could help us understand the mechanisms that cannabis effects and possibly develop drug treatments.

What do you think about the future of your work?

Right now, with our ongoing study, we’re looking at acute effects of THC (tetrahydrocannabinol) versus CBD (cannabidiol). I think that’s probably one of the more promising directions that we’re taking this research. We want to understand the differences between THC and CBD. We are trying to maximize the therapeutic benefits and minimize side effects. CBD doesn’t have the same kind of psychoactive effects that THC has, generally speaking, so you don’t get a high from it. It’s a possibility that CBD might be a better candidate for a therapy, but there are very little data on it so far.

And we’re extending this to other populations as well. This includes HIV patients who suffer from similar neurocognitive impairments. We also plan to investigate the impact of cannabis on older people, who are also at high risk for cognitive decline. With the increasing legalization of cannabis, more older people are turning to cannabis as a medical treatment, but we don’t know how cannabis effects the aging brain. This branch of research is important to me.

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