The New Science of Pot and Appetite
Researchers are trying to untangle the surprisingly complex relationship between pot and appetite.
Economists recently noticed an intriguing trend in American food purchasing. Convenience stores in about 2,000 of the United States’ 3,200 or so counties saw a jump in junk food sales between 2006 and 2016. Potato chips rang up an average sales climb of 5.3% in these counties, and ice cream and cookies weren’t far behind. For stores in the other 1,200 counties, it was business as usual throughout that time period as far as calorie-bomb snacks go, according to a study from the University of Connecticut published in February.
The researchers behind the study argue that the strangely selective geography of amped-up purchasing of packaged sugar and fat can neatly be explained in one word: munchies. The indulgent counties were all in or close to states that legalized recreational marijuana at some point during that 10-year time period, just before sales surged.
The study is a striking way to validate the phenomenon of pot-fueled food cravings. Given what scientists know about how appetite is affected by tetrahydrocannabinol (THC) — the main active ingredient in pot and the one responsible for the “high” — the new data fits well with the experiences of hundreds of millions of people who use cannabis and with what science knows about pot.
Or does it? In hundreds of studies of pot and appetite, the results are, well, disjointed. If there is any sort of consensus, it’s that longer-term use of pot is more closely associated with people maintaining what doctors classify as healthier weights than it is with people ending up glued to the couch, overeating and gaining. “It’s a bit of a paradox,” says Keith Sharkey, a researcher with the Hotchkiss Brain Institute at Canada’s University of Calgary. “On the one hand, we have the munchies, but on the other hand, it seems people who use pot are apparently leaner, at least on an average basis.”
There’s little question that THC can fire up appetite. (CBD, the other main cannabinoid in pot, doesn’t pack a hunger punch.) Scientists don’t agree on what the dominant mechanism is behind the munchies, but there is a buffet line of candidate explanations. In 2014, for example, a large team of European researchers found that activating the CB1 brain receptor — the mechanism on the surface of brain cells that THC targets — boosts the sense of smell in mice, causing them to eat more. In 2015, researchers from Yale and other universities discovered that CB1 receptors also encourage eating by interfering with specific neurons in the hypothalamus that normally shut down appetite when someone is full. And in 2016, U.K. scientists showed how THC ramps up the release of the neurotransmitter dopamine, increasing the pleasure felt when eating.
Whatever the reasons, multiple studies — and not just the junk food sales bonanza for 7-Elevens — have over time confirmed that THC pushes people to eat. In a classic study conducted in the 1980s, Johns Hopkins researchers locked nine men in a lab for nearly a month with no direct contact with the outside world and had them smoke an occasional joint. The pot reliably caused the hapless shut-ins to eat more snack food, upping their total daily calories.
“On the one hand, we have the munchies, but on the other hand, it seems people who use pot are apparently leaner, at least on an average basis.”
THC’s appetite-sharpening power is so pronounced that it’s widely put to use in helping people with cancer, HIV, and other serious diseases that leave them at risk for wasting—essentially, catastrophic malnourishment. “About half of all cancer patients have anorexia at some point, and up to 80% of patients with some types of cancer die from wasting,” says Oscar Arrieta, head of thoracic oncology at Mexico’s National Cancer Institute. Arrieta ran a study last year that showed THC, on average, improved appetite and eating in people with lung cancer. A 2013 study in Finland also found it helpful in increasing food intake in people with anorexia nervosa.
That’s one reason that even the U.S. government has made appetite stimulation in at-risk patients a rare exception to its longstanding stance that marijuana has a high potential for abuse and no medical value. “Increasing appetite to counter wasting and reducing chemotherapy-induced nausea are the only two FDA-approved uses of THC in the U.S.,” says Pal Pacher, a senior investigator at the National Institutes of Health and president of the International Cannabinoid Research Society. States that permit medical marijuana are basically ignoring federal regulations, so far with few consequences. The FDA-approved THC is a synthetic version that could be legally prescribed on an “off-label” basis — that is, for health problems other than the few they’re approved for.
Yet when scientists look at the impact of pot on appetite and overeating — and anticipated weight gain — across large populations of people, the findings are unexpected. In March, a Michigan State University study of health and marijuana-use data on 33,000 people found that the pot indulgers, on average, did a better job than abstainers of fending off weight gain. Other studies have found that waistlines and body mass index (BMI) both tend to go down with increasing use of pot. It seems concerns about the impact of growing recreational pot use on population-level weight gain are potentially unfounded.
As with the munchies findings, scientists offer a plethora of explanations for the seeming protection pot offers from excess weight. Most experts agree that regular exposure to THC leads to CB1-receptor downregulation — meaning the receptor starts reacting less strongly — which in turn tames the munchies effect. And according to research from Indiana University published last year, that same downregulation triggers a series of effects in the body that increases metabolism and reduces the body’s tendency to store excess calories, aiding with weight management.
Meanwhile, the University of Calgary’s Sharkey found that THC seemed to protect mice from obesity by causing changes in their gut bacteria, which have long been linked to excess weight. Yet other experts have suggested that regular THC use may keep weight off by promoting better sleep and reducing stress, leading to less emotional eating and a more active lifestyle for some. (Though it’s important to note that there’s evidence, if somewhat mixed, that heavy use of THC may interfere with the still-developing brains of teenagers).
Assuming there’s a temporary surge in pot use when it becomes legal in a state, it makes sense that there would be an immediate jump in junk food sales as new users get hit by the munchies — but it ought to trail off when those inclined to keep indulging settle into steady use. And that’s what the junk food sales study found. When the laws passed in the state, sales quickly grew, and then, on average, started to shrink back after several months.
Aside from the fact that the munchies tend to be a shorter-term phenomenon, there’s another reason THC seems to be less of a problem for overeating than has been long thought. The CB1 receptor system is a regulatory one, working as a sort of fixer in the brain. That is, it doesn’t always act the same way all the time, but rather adjusts its activity to normalize anything going on in the brain or body that may be out of whack, getting things back into line. That’s probably why some people find pot energizing and others find it relaxing — it depends on whether you’re enervated or stressed out.
At least for now, the available science backs the notion that pot use isn’t likely a major risk for overeating and weight gain
That’s apparently also true of THC-fueled appetite increase — the people who most need it are the ones most likely to experience it, and vice versa. “This is the Janus face of THC,” Sharkey says. “The whole concept of regulation is a key one.” A 2005 Columbia University study found that THC led to a big bump in calorie intake in people with low levels of body fat but not in those with higher levels. For people with diseases that put them at risk for wasting, on the other hand, the appetite increase from THC doesn’t seem to fade as much or as quickly as it does for healthier people. In fact, says Arrieta of the Mexico National Cancer Institute, in his study on people with lung cancer, he observed that THC treatment not only stimulated appetite but also instilled a specific craving for sugary and other high-carb foods — the foods that most efficiently provide the fast calories malnourished people so badly need. “For people who don’t need to gain weight, it probably doesn’t lead to that strong preference,” Arrieta says.
Though science has come a long way in trying to reconcile the seemingly contradictory effects of pot on eating, there’s still a lot left to piece together. Besides needing to clarify all the complex mechanisms at work in how CB1 affects appetite, medicine is still struggling to reliably put the effects to work for people who most need the help with regulating food intake: those with eating disorders and wasting illness, and perhaps even people struggling with overeating.
Pot doesn’t work for all people at risk for wasting — only about half of the people in Arrieta’s study of lung cancer patients benefited — and some simply don’t like how it makes them feel. But that sort of variation is generally true of almost any study of a potential benefit of pot that’s studied in a general population, says the NIH’s Pacher. “Only about a third of people respond well to cannabinoids,” he says. That may be one reason larger population studies are more likely to show that benefits accrue to regular users: Regular users probably become regular users because they’re among the minority that respond particularly well to pot.
Experts say current findings don’t imply that THC should be used as a way to suppress appetite or lose weight. “I don’t think it makes sense to recommend taking up pot to lose excess weight until we have a much better understanding how THC and obesity work,” Sharkey says. In fact, researchers for a while focused on the opposite strategy—enlisting drugs that block rather than activate CB1 as THC does, in the hopes that doing so would suppress appetite. But while those drugs did prove somewhat effective, they came with severe side effects for many people, including depression, insomnia, and nausea — a good reminder that CB1 is associated with a number of important beneficial effects, so blocking it is predictably perilous.
At least for now, the available science backs the notion that pot use isn’t likely a major risk for overeating and weight gain, at least if users aren’t underweight to begin with. It’s true that if you’re new to pot, you may at first get hit hard by the munchies. And if you only very occasionally get high, you might continue to struggle each time with the urge to overeat. But if it’s only an occasional event, pot use is unlikely to lead to excess weight because of munchies.
And you can anticipate the cravings by surrounding yourself with healthier snacks before you toke. Then, if the munchies do hit, you may at least be able to resist the trip to the convenience store.