The Mystery of the Munchies

Currently, 47 states and the District of Colombia allow marijuana for medical use, recreational use, or both to varying degrees. Medical research, including many preclinical studies from my laboratory, largely concludes that low-dose, daily marijuana provides extensive medicinal benefits. The most common reason someone uses a cannabis product is for relief for chronic and temporary pain or relief from anxiety. A common experience associated with medical or recreational use is an increase in appetite, especially for high caloric foods containing fat, salt and sugar. This proclivity, called the “munchies,” has been documented for many centuries. Despite a well-established relationship between marijuana use and increased appetite, the impact that legalizing marijuana may have on obesity rates remains an open and under-investigated question.

Marijuana use is popular. Over 130 million Americans say that they have tried marijuana; over forty million admit using it each month, and over sixty million admit to using marijuana in the past year. Due to changes in state laws, marijuana use has surged over the past decade. Given the prevalence of its continued use, why aren’t marijuana users overweight? Population studies suggest that cannabis users often have lower body mass index and lower obesity rates compared to non-users, even though THC, the active ingredient in marijuana, by acting within the brain’s feeding center, can increase appetite and calorie intake (Sansone & Sansone, 2014). Numerous meta-analyses and population surveys have confirmed the association between cannabis use and reduced body weight.

A recent study (March et al., 2022) examined the effects of legalizing recreational marijuana on obesity rates in the state of Washington, which legalized recreational marijuana use in 2012 and allowed dispensaries to open in 2014. Data obtained from Washington State provided a sufficiently long observational period to draw useful implications. The study reported that the opening of recreational marijuana dispensaries led to decreases in obesity rates. Another study (Sabia et al., 2017) reported that access to medicinal marijuana was associated with a two to six percent decrease in the probability of obesity and between a $58–$115 decrease in obesity-related medical costs per-person.

Why don’t the “munchies” increase body weight?

A recent study (Lin et al., 2023) using animals administered a daily low dose of THC and investigated for lasting changes in energy balance. The study focused on adolescent males that were monitored into adulthood. The daily THC exposure induced an adult metabolic phenotype characterized by reduced fat mass, increased lean mass, and a higher utilization of fat as fuel associated with a partial resistance to diet-induced obesity and enhanced thermogenesis (energy wasting during metabolism). Essentially, the daily, low-dose THC, acting via type-1 cannabinoid receptors, altered the behavior of adipose (fat) tissues. All of the known constituents of the endocannabinoid system are found in white and brown adipose tissues (Jung et al., 2022). Under normal circumstances, this system enhances lipogenesis, i.e., the production of adipose tissue. Therefore, adolescent exposure to THC may promote a long-lasting ‘pseudo-lean’ state that superficially resembles healthy leanness but might in fact be due to a dysfunction of adipose tissues. The fat cells showed another striking change due to a change in gene transcription: they started producing muscle proteins. The long-term consequences of these metabolic changes are yet to be determined.

A final note

Marijuana use is associated with lower body weight; however, studies (March et al., 2022) did not show that THC directly causes weight loss, and marijuana use should not be relied on as a weight-loss method. In multiple studies, overweight adolescents who regularly used marijuana were more likely to remain overweight and become obese as young adults.

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