New research is comparing the weight changes of patients taking different types of antidepressants, one of the most commonly prescribed medications in the United States.

The study, published on Tuesday in the Annals of Internal Medicine, analyzed the data of 183,118 patients across 8 U.S. health systems from 2010 to 2019. It found that some antidepressants were associated with more weight gain than others.

At six months, users of escitalopram (which is sold under the brand name Lexapro), paroxetine (Paxil) and duloxetine (Cymbalta) were 10% to 15% more likely to gain at least 5% of their baseline weight than sertraline (Zoloft) users. 

Bupropion (Wellbutrin) users were 15% less likely to gain weight than sertraline (Zoloft) users, while fluoxetine (Prozac) use was not associated with a weight change.

The study’s authors describe these as “small differences,” but hope the findings will help patients and providers make more informed treatment decisions.

“Patients and their clinicians often have several options when starting an antidepressant for the first time. This study provides important real-world evidence regarding the amount of weight gain that should be expected after starting some of the most common antidepressants,” lead author Joshua Petimar, Harvard Medical School assistant professor of population medicine at the Harvard Pilgrim Health Care Institute, said in a news release.

The study did have some limitations, including a lack of consistent information on medication dosage and adherence. It is also observational, meaning it shows correlation but not causation.

While the study shows certain drugs are correlated with weight gain, it doesn’t necessarily mean the drug is directly causing that weight gain.

For example, if someone lost their appetite due to depression and takes a medication that helps with their symptoms, weight gain could follow without the drug being directly responsible.

In this example, “it’s the treatment of the depression, and then subsequently, regain of appetite that’s causing a weight gain,” explains Dr. Aron Tendler, psychiatrist and chief medical officer at health technology company BrainsWay.

What the study revealed about the amount of people who stopped their medication is also important, Tendler said.

“In general, when someone’s prescribed a medicine, they really should be on it for a year,” he said. “The amount of people that were discontinuing the medicines at three and six and 12 months were incredibly high. Only like 4% of people stayed on their meds for 24 months.”

While the weight gain odds are “not terribly high,” Tendler said, the major takeaway for patients and clinicians is that there are multiple options if someone is concerned about weight gain.

“People can can switch to other medications,” he said, which could help in better adherence and treatment outcomes. “There are also nonmedication treatments like, for example, TMS (transcranial magnetic stimulation)… I think people should be taking that into consideration.”

Government data from 2017 showed antidepressant use rose 65% between 1999 and 2014. Recent studies have shown the impact of the COVID pandemic on increased antidepressant use among young people. For those aged 12 to 25, antidepressant use increased nearly 64% since the start of the COVID-19 pandemic, according to a study earlier this year.