Research explores liberalization of medical marijuana and mental health in the US

The approval of marijuana for medical use has had little effect on the mental health of the general population in the US. But legalization for therapeutic purposes does benefit those for whom it is intended. This is the conclusion of a study by researchers at the University of Basel. The research is published in the journal Health Economics, Policy and Law.

In the US, access to marijuana has been facilitated in most states since the mid-1990s—whether through medical clearance or through decriminalization of recreational use. However, liberalization is still controversial, and the effects on the well-being of specific groups and the therapeutic value of marijuana remain debated.

While some fear negative consequences from addiction, others highlight the potential medical benefits for people suffering from chronic pain, nausea or convulsions.

In a new study, researchers from Basel have now investigated whether medical cannabis legislation in the U.S. is improving the situation for sick people and whether it has a negative impact on the mental health of the overall population.

Probability-based analysis

For their analysis, the researchers combined two large datasets. They used data from almost eight million people who took part in telephone surveys between 1993 and 2018 as part of the Behavioral Risk Factor Surveillance System, which collects data about mental well-being, among other things. But they also used data from the National Survey on Drug Use and Health, which collects information on health-related issues such as drug use in the United States.

The researchers formed different groups using statistical assignment. They include individuals who are highly likely to abstain from using marijuana, to use marijuana as a recreational drug or to use it for medical reasons. It was also possible to identify individuals with a high probability of chronic pain. Mental health was measured using self-assessment, in which respondents reported the number of days they had had mental health problems in the previous month.

Positive effects of therapeutic use

Using statistical methods, the researchers were able to estimate the impact of the legal approval of marijuana for medical use. The result: Easier access improves the mental health of individuals who use marijuana for medical reasons. The same applies to people who are very likely to suffer from pain. The study authors estimate that these two groups spend 0.3 days less per month in poor mental health due to the change in the law.

At the same time, the researchers found no effect on the mental health of recreational users or on younger populations.

"Overall, our results show that medical cannabis legislation in the U.S. benefits the people it is intended for without harming other groups," summarizes the study leader, Prof. Alois Stutzer from the University of Basel.