Bipolar disorder and weed: how experts say they go together

Patients with bipolar disorder who use cannabis have an earlier onset of mental illness, a lifetime of more severe symptoms and more suicide attempts, a new study finds.

The researchers, who did not respond to an interview request, found that people with bipolar disorder who use cannabis are most likely to be single males having a lifetime of psychotic symptoms, have a history of tobacco, alcohol, and psychoactive use, and have attempted suicide. But other researchers who study marijuana and bipolar disorder have doubts. 

“What [the researchers] are saying is that people with bipolar disorder have a number of negative outcomes associated with cannabis use. I think that’s true in general,” said Staci Gruber, an associate professor who studies cannabis in people with mental illnesses at Harvard University. She was not involved in the study. 

The researchers, based out of various institutions in Brazil, sifted through 2,918 bipolar-cannabis articles down to find 53. The researchers noted, among other things, the sample size, age, gender, ethnicity, prevalence of cannabis use, type of bipolar disorder, age at onset of bipolar disorder and lifetime suicide attempts of the subjects included in their studies. The researchers then analyzed these to pull out commonalities. 

Those with bipolar disorder were also significantly more likely to abuse cannabis to the point of having a disorder than those without the mental illness. According to the study, 24% of people with bipolar disorder used cannabis or abused it to the point of harming their lives. The researchers did not respond to requests for further comment on their study. 

Bipolar disorder is a mental condition involving unusual changes in energy, mood and ability to function in daily life. Approximately 4.4% of Americans — or 14.5 million people in the United States — experience bipolar disorder. 

The quarter of bipolar patients who use cannabis, according to the study, could be doing so at the risk of their mental health and lives. 

However, Gruber and other marijuana and bipolar disorder researchers are skeptical of the Brazilian study’s results. Gruber says the study has unaddressed limitations that make it difficult to discern precisely how marijuana affects bipolar patients. 

To create comprehensive studies, also called systematic reviews or meta-analyses, researchers assess numerous scientific papers to tease out broader trends. The findings are generally considered robust because they average the points of numerous peer reviewed papers. 

But Gruber says the study should have disentangled why people use marijuana. Some bipolar patients may use cannabis recreationally to induce an altered emotional or mental state. Others might pragmatically use marijuana to alleviate depressive episodes or calm manic periods. 

Gruber also notes that bipolar patients are likely to use more than one substance at once, meaning they could be consuming marijuana as well as alcohol and other drugs. To say cannabis alone causes negative outcomes skews the context in which the drug was used. 

Trine Vik Lagerberg, a clinical psychologist from the Oslo University Hospital in Norway researching cannabis and bipolar disorder, also sees limitations in the study. She has read high-quality studies indicating correlation between an earlier onset of bipolar disorder symptoms and cannabis use, but she’s more skeptical that marijuana is the sole cause. 

“I am not fully convinced that this relationship is independent from other factors,” Lagerberg says. “With this, I mean that cannabis users may have some characteristics that leave them at greater risk for suicide which does not have to do with the cannabis use itself.”

In other words, here’s what hobbles the efficacy of this study: the failure to differentiate the reason for marijuana use among bipolar patients and the types of marijuana used, as well as the generalized correlation between cannabis use and suicide in bipolar disorder.

With Luxembourg, Mexico, and other countries poised to legalize marijuana, cannabis use is becoming a common pastime in many nations. Comprehensive studies like this one provide stronger support for how marijuana affects people with bipolar disorder, but Gruber notes a more nuanced take on the research is needed to support definitive claims. 

“Why are they using and what are they using? […] Did cannabis use precede the bipolar disorder, or did it follow?” Gruber says. “All these things are important.”