The benefits of legalizing medical marijuana are many—but few would expect that reducing the probability of obesity would be one of them.

Researchers at San Diego State University and Cornell University found that states that legalize pot experience a "two percent to six percent decline in the probability of obesity." The counterintuitive study was recently published in the journal Health Economics.

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After looking at more than 20 years of data from the federal Behavioral Risk Factor Surveillance Survey (including over five million individual survey responses), the researchers determined that "there may be some important physical health benefits associated with medical marijuana laws," the study's lead author, Dr. Joseph Sabia, told ATTN:.

"For younger individuals, we find some evidence that MMLs (medical marijuana laws) may induce substitution away from alcohol and toward a lower-caloric buzz, resulting in lower body weight," Sabia added. "For older individuals, we find some evidence that MML-induced increases in marijuana use may result in effective treatment of medical conditions that impede mobility (such as fibromyalgia or other joint ailments), increasing exercise and reducing body weight."

In other words, the public health impact of medical marijuana laws differs between age brackets. The study seems to confirm something known as the "substitution effect," which refers to the argument that access to legal pot would lead to lower rates of alcohol consumption.

After passing medical marijuana laws, states saw a "3.1 percent reduction in the probability of alcohol consumption and a 4.8 percent reduction in the probability of binge drinking," the researchers wrote. And since high-calorie alcoholic beverages can contribute to weight gain, that reduction seems to have led to lower rates of obesity in legal states.

Of course, marijuana stimulates appetite and gives people the "munchies," but as ATTN: has previously reported, several studies have shown that users are, on average, less likely to have diabetes or problems with obesity than non-users.

Older marijuana users included in the new study also had lower rates of obesity, but not necessarily because they were drinking less alcohol. Instead, the lower rate is related to the effective medical treatment that marijuana offers patients, such as those suffering from chronic pain or arthritis. Having access to medical marijuana—which patients can safely use at their discretion—meant that older users with health complications were able to exercise more and lose weight.

"Some researchers caution against reading too much into the results of this one study," the Washington Post reports. "Rosalie Pacula, director of the BING Center for Health Economics at the RAND Corp., says that the nationally representative BRFSS data is not necessarily the best for sussing out state-level effects. Beyond that, in a number of the states in this study, medical marijuana laws are still very new, so the data on the impact of those laws are relatively sparse."