The Legalization of Marijuana and Its Link to Psychosis

A growing body of scientific studies suggest that marijuana use increases the risk of developing psychotic illnesses such as schizophrenia.  There is an ongoing debate among scientists regarding the exact nature of the risk, including whether the risk is largely confined to those who are already genetically predisposed to these illnesses.  But many scientists have raised the concern whether legalization of marijuana might lead to increases in these illnesses.

Which leads me to the current issue of JAMA Psychiatry, with the viewpoint article Balancing the Public Health Costs of Psychosis vs Mass Incarceration With the Legalization of Cannabis.  In essence, the article argues that marijuana prohibition is a unique risk factor for the development of psychotic illness.  How so, you may ask?   Let’s take a look.

First the authors make the observation that legalization of marijuana is a trend among the states.  They then make the very reasonable claim that marijuana use is associated with an increased risk of psychotic illness.  Then the authors state:

The US has the world’s highest incarceration rate, at 655 per 100 000 adults (followed by El Salvador at 590 per 100 000) and the world’s largest total prison population, at 2 121 600 (followed by China at 1 700 000), according to the World Prison Brief database. The criminalization of cannabis is a significant contributor with approximately 8 million cannabis-related arrests between 2001 and 2010, most owing to possession. Cannabis possession accounts for 36.8% of all drug use arrests in the US according to 2018 US Federal Bureau of Investigation data.

So, as written, the reader is to believe that many marijuana users are languishing in jail for mere possession.  If we dig into the some of the latest DOJ data, however, we learn that about 14% of the state prison population are serving time for drug offenses — and that includes both possession and distribution offenses.   To be sure, it is a nontrivial number of citizens, but anyone who works in the trenches knows that personal possession of small amounts of marijuana does not lead to a lengthy (if any) prison sentence.

Which matters as the authors then state:

Although psychosis is not the only form of psychological distress that may result from incarceration, it is worth considering the consequences of incarceration as a potential trauma or stressor that may contribute to the onset or exacerbation of psychosis given that psychosis risk is a primary argument raised against the legalization of cannabis.

We have known for quite some time that stress can be a precipitating factor for the onset of psychotic illness in people predisposed to it.  But, it is absurd to claim that psychosis can be the direct result of incarceration.  Many factors likely contribute to the onset of psychosis, with age being one of the most robust factors among those who are predisposed.  Another known factor is drug use itself.

I am agnostic about the legalization of marijuana.  But linking the criminalization of marijuana to psychosis by claiming mass incarceration of marijuana users as a robust risk factor is unserious.

To their credit, the authors recognize potential problems with legalization and offer some harm reduction policies:

These may include supply-side efforts, such as age restrictions, minimizing advertising and commercialization, regulating tetrahydrocannabinol content, regulating product types (eg, those encouraging youth consumption), warning labels (eg, black box warnings), racial bias reduction training for law enforcement, criminalizing selling to minors, and considering circumstances in which a misdemeanor might be appropriate.

My guess is that most of these will come to pass as marijuana legalization moves forward.  But I doubt any of it will do much good (except for limiting THC content).  We have warning labels on cigarettes, and their use has declined substantially in the past 50 years, but the decline is due to changing attitudes.  For marijuana, the popular sentiment is quite the reverse.