When Diet Drugs Actually Make You Gain Weight

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Photo: PhotoAlto/Laurence Mouton/Getty Images

When people have tried (and failed) to slim down, they might ask their doctor about one of the four weight-loss drugs approved by the FDA. These treatments, available by prescription or over the counter, work by suppressing appetite and boosting metabolism. But now it turns out that some of them might actually cause people to gain weight, the Washington Post's Wonkblog reports.

Doctors have long believed that people don't understand how weight-loss drugs work — that is, they don't get that they still have to eat well and exercise in order to see results. Recent research published in the Journal of Public Policy & Marketing found that people are indeed deluding themselves: They eat more unhealthy food after simply seeing advertisements for weight-loss pills. (The company behind the drug Alli, for example, tried to raise awareness that the pill can help you shed more pounds as part of a healthier lifestyle, but that it's not a miracle drug.) 

Amit Bhattacharjee, Ph.D., assistant professor at Dartmouth's Tuck School of Business, told Wonkblog that the phenomenon of people gaining weight while taking diet drugs may not be because the pills don't work. Bhattacharjee, who researches consumer behavior, co-authored the study, which found that being exposed to marketing messages for diet pills changed people's eating decisions — and not for the better.

For the study, Bhattacharjee and his colleagues divided 138 participants into three groups: people who saw a message telling them that avoiding fatty foods is the only way to live a healthy lifestyle, others who saw that message followed by ads for an FDA-approved weight-loss drug that claimed to absorb up to 60 percent of the fat in food, and a third group who heard about a treatment that did the same thing, but it was referred to as a natural herbal supplement, not a drug. (Neither formula actually exists.)

Next, each person was given a bowl of 30 small cookies and were told they could eat as many as they wanted. Half got cookies labeled low fat and the rest were given cookies described as "delicious and indulgent." Participants in the group told to ditch fatty foods ate an average of 14 "indulgent" cookies, while people in the drug group ate more cookies (17) and those in the supplement group ate fewer (11). Yes, the researchers only studied marketing messages, but they argue that such unhealthy "adjustments" could be even more profound when drugs are prescribed. "In general, the misunderstanding is that if you take this drug you can lose weight without exerting effort elsewhere to help reduce the risk of gaining weight," Bhattacharjee told Wonkblog. Though supplements are a different story, he said. "There's this notion, I think, that drugs are more targeted or precise, that they do the work for you," he said. "I don't think that's the case for supplements."

If you want to lose weight with or without diet drugs, heed the advice of noted wise person Britney Spears: You better work, bitch.