Why pot gives you 'munchies'; what it means for HIV patients

The same cells in the brain that usually help suppress appetite actually make you want to eat more ... when you are stoned. Researchers at Yale University identified a set of brain cells that reverse their behavior when under the influence of cannabis, and say further research could help prevent malnourishment in severely ill patients who have lost their appetites.

Choreograph | iStock | Getty Images

The scientists initially believed pumping cannabis-like chemicals into the brains of mice would only shut off the parts of the brain that signal fullness or satiety, since marijuana is often associated with boosts in appetite commonly referred to as "the munchies." But when they actually examined mice "under the influence," they found the appetite-suppressing cells were still very much active. Instead of just shutting down and failing to stop the mice from eating, the neurons were releasing chemicals that told the mice to eat more.

They published the results Wednesday in the journal Nature.

"It's like pressing a car's brakes and accelerating instead," said researcher Tamas Horvath, in a press release attached to the study. "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."

This does not mean that smoking pot makes people fat, Horvath noted in a phone interview with CNBC.

Read MoreChina 'blood famine' leads patients to black market

"Interestingly, there is no association between casual marijuana use and obesity," Horvath said. He said that while the neurons are releasing chemicals that stimulate hunger, they are still releasing some appetite suppressing chemicals, as well, and it is possible that those may take over once the effects of the cannabis wear off.

Horvath stressed that scientists have not figured that out yet and that further research is needed. The team would also like to understand what makes these cells switch their behavior and whether the neurons are involved in the general high people feel when they ingest marijuana.

But the experiment may have identified a mechanism in the brain that can help develop better strategies for treating sick people who struggle with appetite loss, which can itself be debilitating and dangerous.

"There are diseases where you have loss of appetites in patients, such as cancer and HIV patients," Horvath said. "That can result in malnutrition, which can be a major factor to the onset of death. So if you can get these patients eating, you can get them healthier, and up and moving again, you can improve their chances of survival."