Some antidepressants may cause more weight gain than others

Weight gain has long been a common side effect of antidepressants, but some of them are more likely to cause extra pounds than others, according to a new study.

The study, published Monday in the journal Annals of Internal Medicine, analyzed the electronic medical records of more than 183,000 U.S. patients who were new to antidepressants and tracked their weight for 24 months.

After six months, patients taking Lexapro, Paxil or Cymbalta had a 10 to 15 percent higher risk of gaining a clinically significant amount of weight, defined as at least 5 percent of their baseline weight, compared with Zoloft users. Those taking Wellbutrin were less likely to have this type of weight gain. The study included both brand-name and generic forms of each drug.

“Many patients worry about gaining excess weight when they take an antidepressant,” said Joshua Petimar, an assistant professor of population medicine at Harvard Medical School and the Harvard Pilgrim Health Care Institute, and lead author of the study. That may be especially true for patients with a pre-existing health condition such as diabetes.

In addition, some patients stop taking their antidepressant — even if it is effective — because they do not like the weight they have gained. “That can also lead to a range of adverse outcomes, such as increased risk of hospitalization or relapse of symptoms,” Dr. Petimar says.

In the study, patients taking Lexapro or Paxil gained an average of about a pound more after six months than those taking Zoloft, which was the most prescribed of the eight antidepressants tracked. People taking Cymbalta, Effexor or Celexa also initially gained more weight than Zoloft users, but in each case it was less than a pound. Those taking Wellbutrin, however, gained less weight than those taking Zoloft.

The study showed some degree of weight gain with all of the antidepressants. And most of the people in the study were overweight or obese at the start, which representative of the American population.

“It doesn’t really matter which one you choose,” said Dr. David J. Hellerstein, a professor of clinical psychiatry at Columbia University Irving Medical Center who was not involved in the study. “It’s the same problem everywhere.”

Choosing the right antidepressant can be a balancing act between efficacy and side effects, he added. And deciding which side effects you’re willing to deal with can be tricky.

Although Wellbutrin users are less likely to gain weight, for example, that drug “causes a lot of dry mouth and has caffeine-like side effects,” Dr. Hellerstein says. “Some people don’t like that.”

Moreover, experts say it is difficult to make general statements about whether a specific antidepressant causes someone to gain weight, especially given variations in diet and exercise, as well as genes and medical history.

The study had several limitations. The researchers were unable to verify that each patient was taking an antidepressant for the first time. Additionally, the data did not include consistent information about the dosage of the medication, meaning the researchers could not determine how dosage might affect weight gain.

In addition, some people may have gained weight during the study period even if they weren’t taking medication, Dr. Hellerstein said. If the study had included a comparison group of people who weren’t taking antidepressants, that could have helped determine the extent to which the medication contributed to the weight gain, he added.

Since some medications were associated with sustained weight change over the two-year study period and others plateaued, more research is needed to know whether these curves can be replicated in a future study, Dr. Petimar said.

“It generates some interesting theories about why the trajectories might be different,” he added.

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