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If you smoke or eat pot, you might have encountered the “marijuana munchies,” or the desire for salty, sweet or fatty carbohydrate-rich foods when using the drug.

But what exactly are those cannabis-related cravings all about? Why do they happen?

Well, you can blame them on the drug’s active ingredient tetrahydrocannabinol, or THC.

THC is responsible for the “high” many people experience when using cannabis. But it’s also primarily responsible for the increase in food cravings people get when taking the drug.

The brain is divided into regions: Some areas control our moods, whereas others influence our appetite, causing us to eat or stop eating. Anytime we consume a drug, it gets distributed everywhere, so when THC enters the parts of the brain that affect mood, it stimulates euphoria, explained Gary Wenk, director of neuroscience undergraduate programs at the Ohio State University and author of “Your Brain on Food.” And when THC reaches the area of the brain that influences appetite, it will “stimulate you to eat,” Wenk said.

Though research points to various possible mechanisms, the ability of cannabis to increase appetite is “very well-documented,” said Ginger Hultin, a registered dietitian and spokeswoman for the Academy of Nutrition and Dietetics.

Research involving cannabis has revealed that THC stimulates the endocannabinoid system, a complex area of the brain that regulates feeding behavior and energy balance. “It’s hitting on some primitive areas of the brain, things that control appetite and emotions,” Hultin said.

“THC interacts with receptors in our brain that regulate emotions, pain and our sense of smell and taste,” said Janice Newell Bissex, a registered dietitian. “It can also promote the release of the hormone ghrelin, which stimulates hunger.”

The scientific mechanisms are complex. According to one animal study, by binding to receptors in the olfactory bulb in the brain, THC appears to enhance our sensitivity to smell, which would make aromas from food more potent and cause us to eat more.

Other research has revealed that neurons that normally turn off when eating actually stimulate more eating when marijuana is used. “The neurons that typically control our level of satiety can be usurped when marijuana is consumed,” Wenk said.

THC also increases the release of dopamine, which enhances the pleasure of eating, explained Bissex. In addition to making food more enjoyable, dopamine – a brain chemical that helps to control the brain’s reward and pleasure centers – can lower inhibitions, Hultin explained.

“Lowering inhibitions is a big challenge with weed and alcohol,” she said. “People know what they should be eating, but all of a sudden, their inhibitions are down, and they are eating unhealthy foods.”

The effects are intensified among those who carry extra pounds. “In obese people, when they see a chocolate malt, it will activate their dopamine system to a bigger degree than non-obese individuals,” Wenk explained. As a result, “these individuals might be primed to have a bigger munchie response.”

Hultin, who helps healthy individuals maintain good eating habits in the marijuana-legalized state of Washington, has seen how the drug can increase appetite and affect one’s weight.

“People will say they’ll use marijuana to relax … but it will spike their appetite for chips and ice cream … and unhealthy foods they want to be avoiding,” she said. These people are able to link their weight struggles to their use of marijuana, she explained.

Consuming marijuana in foods poses a unique challenge, as edibles can compound THC’s effects on appetite and weight. For example, sugary edibles such as candies, cookies, lollipops and brownies not only contribute calories, which can result in weight gain, but they can cause spikes and drops in blood sugar, which can increase cravings, Hultin explained.

The research involving cannabis’ effects on appetite hasn’t gone unnoticed by the pharmaceutical industry.

“There’s a really fascinating story involving the drug rimonabant,” Wenk said. “Many years ago, researchers thought if the munchies are due to THC stimulating feeding receptors and inducing us to eat high carbs, then why can’t we design a drug to block those receptors?”

Researchers sought out to test whether they could manipulate feeding centers that play a role in determining our urge to eat.

“They tested the drug … and people lost weight and gave up their interest in cheeseburgers and fries and alcohol and cigarettes,” Wenk said. “They thought, ‘This is an amazing drug!’ People were getting thinner and giving up their addictions!”

But researchers soon realized that it wasn’t safe to block all of a person’s endocannabinoid receptors, which control mood and feeding behaviors, all of the time. “People became depressed and started committing suicide,” Wenk said. Clinical trials were stopped, and the drug was pulled from the market.

The findings revealed that you can’t selectively block some endocannabinoid receptors and not others.

“The euphoria we experience when we eat something tasty or enjoy the company of a loved one involves our brain’s internal endocannabanoid system saying ‘thank you.’ However, if you block the action of this system, you take away your ability to feel joy all the time,” Wenk said.

For people with illnesses that dull appetite, the increased hunger produced by the drug can be therapeutic. “While some might find this an unwanted side effect, appetite stimulation is exactly the result that many elderly patients or those suffering from cancer or HIV are looking for,” explained Bissex, who recently became a holistic cannabis practitioner after watching her father’s chronic pain ease after using marijuana for medicinal purposes.

“My dad tried cannabis when traditional pain meds were marginally effective and caused terrible side effects, including constipation and fatigue. Not only did he get relief from his pain, but he also saw a welcomed increase in appetite,” she said.

Hultin previously worked as an oncology dietitian and saw the drug’s effects on cancer patients firsthand. “I have had patients literally tell me, ‘I cannot eat unless I am using marijuana.’

“When you see someone so sick in front of you, and you just want to help them eat, and then they say, ‘I can’t eat without this substance,’ I say, ‘This may be what you need,’ ” Hultin said.

Whether you choose to use pot or not, perhaps the simplest way to sum up the role that marijuana plays in the control of appetite is that it helps the brain ensure our survival – that is, to make sure we eat.

“The brain has only two jobs: the survival of its owner and procreation,” Wenk said. “Neither of these are possible without eating.”

If you are concerned with weight gain when using cannabis, Bissex recommends making sure healthy snacks are available. “Stocking up on popcorn, veggie sticks with hummus, whole-grain crackers with a low-fat dip and tortilla chips with salsa might satisfy the munchies without taking in too much sugar and calories.”

Lisa Drayer is a nutritionist, an author and a CNN health and nutrition contributor.