Ryan McLaughlin was curious about what transpires within a rat’s brain when it becomes intoxicated. More precisely, he wondered if a well-fed, satisfied rat — one that had eaten sufficiently and had absolutely no biological urge for additional food — would still pull a lever for treats after inhaling cannabis vapour. The outcome was clear-cut. “The sober animals are kind of like, ‘I’m full. Why should I care?’ They don’t exert any effort whatsoever,” states McLaughlin, a professor at Washington State University’s College of Veterinary Medicine. “But you get them stoned again, and although they’re now full and have eaten, they immediately return as if they’re starving.”
This observation, trivial to anyone who has ever scavenged a kitchen at midnight, proves to have significant scientific implications. A new study published in the Proceedings of the National Academy of Sciences (PNAS) represents one of the most thorough examinations of “the munchies” conducted to date, executing parallel experiments in both humans and rodents to determine not just whether cannabis boosts appetite but exactly where in the body this effect originates.
Parallel Experiments: From Pullman to Calgary
The human segment of the study involved 82 volunteers ranging from ages 21 to 62 from the Pullman, Washington area, who were randomly assigned to vaporize either 20 or 40 milligrams of cannabis, or an inert placebo. To replicate real-world usage, researchers employed a “whole-plant” vapor method instead of synthetic THC injections. This “translational” approach enables scientists to observe how the complex chemistry of the plant—not merely a single molecule—interacts with human behavior.
Then came the snack table. The findings were remarkable in their uniformity: independent of BMI, when the participants had last eaten, their gender, or the amount of cannabis consumed, those who actually became high consumed considerably more food. All of it. Within the initial half-hour of snack availability, the effect was already evident. One particular result baffled Carrie Cuttler, director of the Health and Cognition Lab at WSU and a research leader. “Beef jerky was among the top choices for intoxicated individuals, which I don’t quite grasp. Honestly, I would have expected chocolate, chips, Rice Krispies treats — items like that.”
Water also emerged as a leading preference, likely a physiological response to xerostomia (cottonmouth), triggered by THC binding to receptors in the salivary glands.
The rat experiments at the University of Calgary, led by Matthew Hill and Catherine Hume, reflected these findings with remarkable accuracy. The animals were placed in operant chambers — essentially boxes where pulling a lever dispensed food — and presented with various choices following cannabis vapour exposure. Satiated rats who typically wouldn’t make an effort suddenly worked energetically for food. “The same phenomenon we observed in humans was mirrored in the rats,” says Hill. “We had kind of expected it would increase their desire for carb-rich foods, but that didn’t appear to be the case. It just seemed to be any food.”
The Mechanism: A Top-Down Brain Hijack
This is significant as it begins to illuminate the underlying mechanism. Previous hypotheses suggested that cannabis might selectively heighten the allure of sweet or fatty foods — intensifying the hedonic attraction of particularly enjoyable options. Instead, what the study unveiled was something more comprehensive: cannabis seems to entirely bypass the brain’s satiety signals, enhancing motivation to consume and diminishing what researchers refer to as “food reward devaluation.”
What is Food Reward Devaluation?
Normally, as you eat, the pleasure derived from food diminishes—a biological “stop” signal. This study demonstrated that THC maintains the reward value, meaning the tenth bite of food feels as gratifying as the first, regardless of how full the stomach is.
The body naturally produces its own cannabinoids, molecules that bind to the same receptors as THC, and assist in regulating everything from mood to pain to appetite. In the hypothalamus, this endocannabinoid system plays a role in hunger signaling. “But THC takes over that entire system,” explains McLaughlin. “So even if you’re not particularly hungry, THC can stimulate cannabinoid receptors in the brain and induce a feeling of hunger.”
To verify that the action occurs in the brain rather than the gut, the Calgary team conducted a pharmacological experiment: they obstructed cannabinoid receptors in the peripheral nervous system of rats — the network that traverses the digestive tract.