These pot-infused nachos feature shrimp and crab. (Courtesy of Bruce Wolf)

Pot science: Here are the neurological reasons marijuana gives you munchies

The munchies are more than a punchline. The munchies — “that inexplicable drive to eat, stimulated by the active ingredients of marijuana, the cannabinoids,” as described by writers Sachin Patel and Roger D. Cone — are a legitimate, nearly universally felt side effect from the consumption of marijuana. And there are specific scientific reasons for why we’re inclined to eat, whether we’re hungry or not, after getting high.

What are those scientific reasons? We weren’t completely sure until today, when an important new study out of Yale was released in science journal Nature illuminating some (but not all) of the background on munchies.

The munchies come down to a certain region of the brain that scientists often link with feelings of sexual arousal and hunger. From Patel and Cone’s Nature article accompanying the new study:

That cannabinoids can act at several brain regions to stimulate food intake is well established. So the striking lesson here is not so much the orexigenic (appetite-stimulating) effect of cannabinoids through yet another of the many brain circuits involved in feeding behaviour. It is rather that cannabinoids can subvert an appetite-inhibitory (anorexic) circuit to become orexigenic, which indicates that the POMC (pro-opiomelanocortin) circuit may be even more complex than previously thought. Another challenging concept arising from the present work is that, during the acute orexigenic response, cannabinoids stimulate these neurons partially through intracellular CB1Rs (for cannabinoid receptor 1), rather than through the more usually observed actions of cannabinoids at nerve terminals to regulate the release of substances such as the inhibitory neurotransmitter GABA.

“It’s like pressing a car’s brakes and accelerating instead,” Yale researcher Tamas Horvath, a lead author on the study, told CBS News. “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.”

From the CBS News report:

Researchers have long known that cannabinoids, the active ingredients in marijuana, are associated with increased appetite and that activating the brain’s cannabinoid receptor 1 (CB1R) can contribute to overeating. But this study on mice went a step further and found that pot actually activates certain neurons (called the pro-opiomelanocortin (POMC) neurons) that are considered key drivers for inhibiting hunger.

Horvath initially thought their findings were a “mistake.” How could marijuana reverse the function of neurons? So they went back to the mice and tested what happened when they suppressed the action of POMCs versus turning them on and turning them up.

“If we inhibited these neurons, then cannabinoids did not induce that type of feeding as they would induce normally,” Horvath said. “If we over-activated these cells, then the cannabinoids induced much more feeding than they normally induced.” The mice “ate like hell.”

You have to love that scientific speak: “Ate like hell.” Been there, done that?

The munchies are an undeniable byproduct of getting stoned, the scientists said.

“For anyone who’s experienced it — you realize that’s exactly what’s happening,” Horvath told NPR. “You just can’t stop, no matter how much you put in your mouth.”

More on the study’s methodology, from NPR’s report:

One caveat is that the study — which appears online in the journal Nature — was done on mouse brains, not human ones. But Horvath says the hypothalamus is such an ancient part of the brain, something that evolved before mammals, that he’d “bet his life” the way these neural circuits work in mice is the same in humans. (Rockefeller University neuroscientist Jessica) Barson says that until you do the experiment with humans, “you can’t know for sure, but it’s reasonable to conclude that it’s the same thing.”

The study is not, however, the final missing piece of the munchies mystery. A lot of other neural processes get layered on top of what goes inside the hypothalamus, and cannabinoids affect those other parts of the brain as well. Last year, researchers found that cannabinoids lit up the brain’s olfactory center, making mice more sensitive to smells. Before that, other researchers discovered cannabinoids were increasing levels of dopamine in the brain; that’s the swoon that comes with eating tasty things.

The Washington Post opines that this research could lead to “new approaches to treating obesity.”

Beyond merely figuring out the neurological mystery behind the munchies, Horvath and other scientists are hoping that a clearer understanding of the appetite triggers in the brain could lead to an array of practical uses. For instance, it could lead to new medications, perhaps even a pill, to jump-start hunger in cancer patients who often lose their appetite during chemotherapy. (Some patients already use marijuana to relieve pain, control nausea and vomiting and stimulate appetite.) At the same time, the ability to block cannabinoid receptors in the brain eventually could lead to new approaches to treating obesity.

Read the full study here.