Why does marijuana give users the munchies?

Why does it hunger? Nick Vedros & Assoc/Getty

Whether you're a wake-in-bake aficionado or merely enjoy a good stoner comedy, you've probably come across the undeniable link between cannabis consumption and increased appetite for snacks. But do you know why it occurs?

THC and the Brain

Human civilization has a long history with marijuana. Chinese records of cannabis cultivation date from the 28th century B.C.E. And traces of THC -- its principle psychoactive chemical -- popped up in a nearly 3,000-year-old Egyptian mummy.

Once in your bloodstream, THC heads to the brain. Here, it gets down to business altering mood, perception, cognition, motor coordination and appetite.

We're talking a strong uptick in appetite here, too. Some even describe the sensation as "uncontrollable," producing a fierce hunger even in the wake of a full belly. The user shouldn't feel peckish, but the THC manages to flip the brain's appetite switch to the "Hungry Hungry Hippos" setting.

Researchers have long recognized that the brain's cannabinoid receptor 1 (CB1R) can contribute to overeating, and now a new study from the Yale School of Medicine sheds more light on the particulars of what's going on.

The New Study

By manipulating the cellular pathway that mediates marijuana's action in the brains of transgenic mice, they observed the key role played by a group of nerve cells called pro-opiomelanocortin (POMC ) neurons.

Normally, these are considered key drivers in reducing eating when full. Smoke a normal tobacco cigarette and the nicotine makes POMC neurons more active, curbing hunger.

And yet the THC actually reduces hunger by activating these same POMC neurons. That's right, the same mechanism that normally turns the "Hot Donuts" sign off, turns it on -- a fact that surprised the Yale researchers.

While more work is required to validate the findings, scientists hope that increased understanding of THC's effect on appetite will enable the development of better appetite manipulators, aiding in both weight loss and the care of cancer patients, who often experience decreased appetite during treatment.

About the Author: Robert Lamb spent his childhood reading books and staring into the woods — first in Newfoundland, Canada and then in rural Tennessee. There was also a long stretch in which he was terrified of alien abduction. He earned a degree in creative writing. He taught high school and then attended journalism school. He wrote for the smallest of small-town newspapers before finally becoming a full-time science writer and podcaster. He’s currently a senior writer at HowStuffWorks and has co-hosted the science podcast Stuff to Blow Your Mind since its inception in 2010. In his spare time, he enjoys traveling with his wife Bonnie, discussing dinosaurs with his son Bastian and crafting the occasional work of fiction.