Increasing consideration of the public health impact of cannabis legalization has led to a closer look at its impact on obesity. Cannabis is associated with weight loss and decreased opioid use, in spite of the munchies and the gateway theory of addiction. Weight loss and the consequent savings on health care for obesity-related complications need to be considered in economic and political analyses of cannabis legalization. The importance of these factors is bolstered by a new longitudinal study from researchers at Michigan State University, who analyze data from roughly 40,000 people over three years. Any amount of cannabis use was associated with lower BMI, but persistent users had the greatest decrease in BMI. Longitudinal studies, which track how individuals change over time, are more able to draw conclusions about cause and effect than other kinds of surveys. There are limitations, however. For example, cannabis users are more likely to smoke tobacco, which is known to reduce appetite and lower weight. As well, “use” was defined as any cannabis exposure in the past 12 months, but did not take into account the frequency and duration of use. Such considerations limit more detailed conclusions, although the study adds to the growing consensus that cannabis use leads to weight loss.