Aside from squinty eyes and a thought-provoked mind, one of the most well-known effects of marijuana is that powerful surge in appetite known as “the munchies.” A team of researchers from the Yale School of Medicine recently set out to track down the neurons in the pot smoker’s brain that are responsible for that uncontrollable urge to eat after a hit. Their findings appear in the journal Nature.

"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," the study’s lead author Tamas Horvath, professor and director of the Yale Program in Cell Signaling and Neurobiology of Metabolism, said in a press release. "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."

Researchers monitored the circuits wired throughout a mouse’s brain in order to see how appetite is influenced by marijuana. They already knew that cannabis is associated with increased appetite, regardless of how full you may be, because of its ability to activate the cannabinoid receptor 1 (CB1R) inside the brain. Horvath and his team are also trying to figure out if the CB1R receptor has anything to do with the high that comes along with cannabis use.

"This event is key to cannabinoid-receptor-driven eating," said 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."

The medicinal strand of marijuana has been widely used throughout hospitals to help cancer patients who oftentimes lose their appetite during chemotherapy treatments.  The effect that marijuana’s active ingredient tetrahydrocannabinol (THC) has on a brain not only stimulates their appetite, but also fits into the brain’s olfactory bulb, according to The Smithsonian. This receptor is responsible for the food we smell, and THC significantly increases the person’s ability to smell food, which in turn causes salivation and generates a hungrier response.

If the brain is able to interpret an enhanced version of smells or tastes, it’ll engage and strengthen that portion of the brain, creating a fixation on food. However, some will say it’s not necessarily an uncontrollable urge to eat, but rather an overwhelming desire to engage that part of the brain.  

Source: Horvath T, Koch M, Varela L, Kim JG, Kim JD, and Hernandez F. Nature. 2015.