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Why Pot Gives People the Munchies

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It may be the most notorious side-effect of smoking dope — that sudden urge to eat anything and everything in the house. It starts with corn chips but takes you all the way through the stale cornflakes in the very back of the last kitchen cabinet.

Now, scientists think they may have a handle on just why marijuana gives people the munchies. And the discovery may help pave the way for designing better obesity drugs, because it might help explain why so many of us eat even when we are not hungry.

Chemicals called cannabinoids in marijuana appear to make brain cells switch their normal functions, Tamas Horvath of Yale University and colleagues report in the journal Nature. They ran their tests in mice, but the brain system works similarly in humans.

"It fools the brain's central feeding system."

Specifically, cannabinoids activate a group of brain cells called pro-opiomelanocortin (POMC) neurons. They are found in the hypothalamus and regulate appetite.

"It fools the brain's central feeding system," Horvath said in a statement. "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 turns out that the cannabinoids were not simply acting directly on the POMC cells. They were also activating neighboring neurons that are supposed to shut down those cells.

"Together, these results uncover a previously unsuspected role of POMC neurons in the promotion of feeding by cannabinoids," the researchers wrote.

It’s not the first time scientists have focused on munchies-inducing effect of marijuana. About 10 years ago, scientists reported on a drug that turned off the same brain circuit that causes the munchies. It was called rimonabant, and drug maker Sanofi started to market it under the brand names Acomplia and Zimulti.

But the drug caused depression and was pulled off the market soon after.

So this discovery isn’t a slam-dunk. It’s an unexpected switch in function and shows that the mechanisms that regulate brain cells are complicated and unpredictable, the researchers said.

Another possible use for the research: it may help researchers develop marijuana-based drugs to aid patients with anorexia, including anorexia caused by diseases such as cancer and AIDS.

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