Why smoking pot causes the ‘munchies’

"It's like pressing a car's brakes and accelerating instead," says Tamas Horvath. "We were surprised to find that the neurons we thought were responsible for shutting down eating, were suddenly being activated and promoting hunger, even when you are full." (Credit: Seth Anderson/Flickr)

Smoking marijuana causes neurons that normally suppress appetite to signal an uncontrollable urge to eat instead.

For a new study, researchers monitored the brain circuitry that promotes eating by selectively manipulating the cellular pathway that mediates marijuana’s action in transgenic mice.

“By observing how the appetite center of the brain responds to marijuana, we were able to see what drives the hunger brought about by cannabis and how that same mechanism that normally turns off feeding becomes a driver of eating,” says Tamas Horvath, professor of neurobiology and of obstetrics, gynecology, and reproductive sciences at Yale University.

“It’s like pressing a car’s brakes and accelerating instead. We were surprised to find that the neurons we thought were responsible for shutting down eating, were suddenly being activated and promoting hunger, even when you are full. It fools the brain’s central feeding system.”

In addition to helping explain why you become extremely hungry when you shouldn’t be, the new findings, published in  Nature, could provide other benefits, like helping cancer patients who often lose their appetite during treatment.

Researchers have long known that using cannabis is associated with increased appetite even when you are full. It is also well known that activating the cannabinoid receptor 1 (CB1R) can contribute to overeating. A group of nerve cells called pro-opiomelanocortin (POMC) neurons are considered to be key drivers of reducing eating when full.

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“This event is key to cannabinoid-receptor-driven eating,” says Horvath, who points out that the feeding behavior driven by these neurons is just one mode of action that involves CB1R signaling. “More research is needed to validate the findings.”

Whether this primitive mechanism is also key to getting “high” on cannabis is another question that Horvath, who is also director of the Yale Program in Cell Signaling and Neurobiology of Metabolism and chair of the Section of Comparative Medicine lab, is aiming to address.

The National Institutes of Health, the American Diabetes Association, The Klarmann Family Foundation, the Helmholtz Society, and the Deutsche Forschungsgemeinschaft (Obesity Mechanisms) funded the study.

Source: Yale University