Smoking marijuana has long been known to give people the “munchies,” but a recent study has suggested that its legalization for medical purposes could actually lead to a decrease in obesity rates. This is due in part to marijuana’s pain-killing properties, which enable users to lead more active lives, and in part to a “spillover” effect, whereby increased availability causes some people to smoke marijuana instead of consuming high-calorie alcohol.

The study, which was published in Health Economics, examined data recorded between 1990 and 2012 as part of the Behavioral Risk Factor Surveillance System (BRFSS), which contains information about various aspects of participants’ lifestyles. By tracking changes in these responses as new medical marijuana laws (MMLs) came into effect, and cross-referencing these changes with fluctuations in participants’ body mass, the researchers concluded the introduction of these laws generated a measurable improvement in obesity.

Interestingly, this effect cannot be attributable to a single cause, but is instead produced by a range of factors that apply to specific demographic groups. For instance, the study found that older people tend to use medical marijuana to help treat debilitating pain, and are subsequently able to exercise more as they become less hindered by physical disorders.

Younger people, meanwhile, reported that the spillover of medical marijuana into the recreational market had sparked a decrease in street prices, which then encouraged them to seek out the substance as a partial replacement for alcohol. Since the average serving of beer contains around 150 calories, and the standard glass of wine contains 120, a switch to smoking instead of drinking may well be responsible for reductions in body mass, the paper claims.

^{For certain groups, medical marijuana availability leads to a decrease in high-calorie alcohol consumption, while for others it helps to relieve pain and enables a more active lifestyle. Image credit: Stanimir G.Stoev/Shuttertock}

This is in spite of the fact that marijuana contains cannabinoids, which bind to the brain’s CB receptors, causing signals to be transmitted to various parts of the body including the gastrointestinal system. These signals influence feelings of hunger, and are responsible for the “munchies” effect commonly associated with smoking marijuana.

Regardless, the study authors conclude that “the enforcement of MMLs is associated with a 0.4% to 0.7% reduction in body mass index (BMI) and a 2% to 6% reduction in obesity.” They also note that these effects tend to increase around five years after MMLs are implemented, which corresponds with the logic that states that the benefits of medical marijuana legalization should take a while to manifest themselves.

Speaking to IFLScience, study co-author Tim Young of San Diego State University said that this data represents just “one of the first steps towards understanding the broader public health implications of passing these [medical marijuana] laws.” As such, he recommends caution when drawing conclusions about the role of cannabis in treating obesity, explaining that there is “not necessarily a direct relationship of causation from starting to intake marijuana to seeing declines in body mass,” since these results were mediated via wider lifestyle changes.

However, he is on the whole confident that the positive changes were driven by the use of medical marijuana rather than any non-related factors. “I’ve thought a lot about different things that could be at work and I can’t think of anything that could be driving those results besides these laws,” he said.