As Maryland legislators appointed to the “Cannabis Workgroup” begin their study of the pros and cons of marijuana legalization, they should pay particular attention to the mental health risks of this drug. Unfortunately, they may not have heard much about the epidemiology of psychosis associated with marijuana use, since relevant U.S. expertise lags behind Western Europe, Canada and a couple of countries in the southern hemisphere.
Epidemiological studies are observational, not interventional, so our slow entry into the field has nothing to do with the illegal status of marijuana. Instead, I would point to our lack of centralized health care, which would otherwise facilitate collection of data on large populations — data pertaining to health status, history of health-related habits and key demographics. Another factor is how biomedical research here is tightly coupled to the pharmaceutical industry, a sector less interested in environmental factors that cause disease than in developing blockbuster drugs.
From the perspective of many of us who have researched the causes of psychosis in the laboratory or in clinical settings, the book by journalist Alex Berenson “Tell Your Children the Truth About Marijuana, Mental Illness, and Violence” provides an important wake-up call for America. The former New York Times business reporter wrote it after his psychiatrist wife suggested he learn more about the topic. But it’s a lone voice of caution on the national stage. While Medical associations in the U.S. have issued position papers citing harms of marijuana, these documents are largely buried in their websites out of view.
Here’s what you should know: Researchers looking for a dose-response correlation found that the heavier the marijuana use, and the more potent the product, the more likely a psychotic outcome like schizophrenia. Daily use of potencies considered moderate by current U.S. standards increases risk 4- to 5-fold.
Some will argue that individuals with psychosis who use marijuana are merely self-medicating pre-existing symptoms, despite research showing symptoms remit for many who quit using, and return if they use again. Studies in Europe and New Zealand of thousands of teens followed through young adulthood, demonstrated the marijuana habit preceded psychosis in the majority of marijuana users who developed it.
Yes, initial psychotic symptoms associated with marijuana are usually temporary, and only 12 percent to 15 percent of users reported these transient symptoms with lower strength marijuana common in the 1900s — symptoms like paranoia, delusions or auditory hallucinations. But 35 percent of those who experience such occasional symptoms can be expected to transition to a full psychotic break, a cluster of intense symptoms happening at once.
Could other drugs laced into marijuana explain these devastating outcomes? The answer is a resounding no. When compared to other recreational drugs that cause a full psychotic break (LSD, PCP, cocaine, amphetamine, methamphetamine), marijuana-induced psychotic breaks were the most likely to lead to a diagnosis of schizophrenia eight years out. As I like to say, lace your LSD with a little marijuana and you’re more likely to become psychotic.
Psychiatrists who admit marijuana can trigger schizophrenia will often maintain it does so only in those with a genetic predisposition. If asked, they would not be able to tell you the precise genetic predisposition, just that it derives from family history, much like susceptibility to heart disease. Yet, clinical studies in the U.K. have shown that 40 percent of individuals lacking a 1st degree family history of psychosis will exhibit transient psychotic symptoms when administered a moderate dose of pure THC. And for users and non-users alike, relatively few of those diagnosed with schizophrenia have any family history of schizophrenia in a 1st- or 2nd-degree relative.
The causal link between marijuana use and the development of psychosis is quite simply the most well-replicated, high-impact finding in schizophrenia research today. Given current use rates and the strong potency of the drug available, it stands to be responsible for a larger proportion of schizophrenia cases than any other established factor. Who may be at risk cannot be reliably predicted. The time is long overdue for the surgeon general and American neuroscientists and psychiatrists, along with their universities and professional societies, to inform the public and for journalists to pay heed.
Christine L. Miller (firstname.lastname@example.org) is a neuroscientist and author of “The Impact of Marijuana on Mental Health in: Contemporary Health Issues on Marijuana” (Oxford University Press, 2018).