Cannabis is not a gateway drug, says new study

Has the theory of cannabis as a stepping stone to drug escalation been definitively laid to rest?

In a study published at the beginning of January 2023, American researchers refute the idea that cannabis is a gateway drug, a substance that leads to the consumption of other «harder» drugs.

The study shows that American states that have legalized cannabis have not seen an increase in substance use disorders or the use of other illicit drugs. Rather, it reveals that cannabis legalization can reduce alcohol-related problems.

What does the study say?

Using data from two studies conducted over several decades at the University of Colorado and the University of Minnesota, the study involved more than 4,000 twins, 40 % of whom lived in a U.S. state where cannabis was legal (Colorado) and 60 % in a state where cannabis was not legal (Minnesota).

Using twins in the study «controls for a wide range of variables, including age, social background, early family life and even genetic inheritance,» said author John Hewitt.

The subjects were studied at two different times: before 2014, when the Colorado opened its first dispensaries, and after. The study measured consumption of alcohol, tobacco, cannabis and illicit substances, as well as mental health.

«For low-level cannabis use, which was the majority of users, among adults, legalization does not appear to increase the risk of substance use disorders,» said study co-author Dr. Christian Hopfer. This was the case for both cannabis and other substances.

Nor did the study find any link between cannabis legalization and cognitive problems, psychological, social, relational or financial.

She adds that cannabis abuse prevention and intervention would be better targeted at risk factors, such as family history or mental disorders.

It's important to note that the study is limited in some respects, since it only involved individuals from Minnesota and Colorado, and 92 % of the participants were white. In addition, the subjects were «characterized by low levels of substance use and psychosocial dysfunction», according to the study.

The end of a prohibitionist theory?

The theory that cannabis is a gateway drug was born in the 1970s, as part of the political campaign against drugs, which publicly sought to reduce drug use in the United States, but under the guise of public health, aimed at mass incarceration of people of color. Today, cannabis is often presented as a gateway drug to block regulatory efforts.

«We really didn't find support for many of the harms people fear with legalization,» said lead author Stephanie Zellers in a press release. «From a public health perspective, these results are reassuring.».

The study's authors note that, while legalization does not lead to substance abuse disorders, whether cannabis or another substance, more research is needed on the plant, particularly on THC potency, dosage and consumption patterns.

A study published last year in the Journal of Adolescent Health came to a similar conclusion, estimating that the legalization of cannabis has not led to «a dramatic increase in the consumption of alcohol, cigarettes and non-prescribed opioids».