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People who took antidepressants for a long time gained, on average, twice as much weight as people who never took them. The effect grew stronger over time, even among those who dieted and exercised.
Dr. Gabriela Lugon, a researcher at Del Mar Hospital and Pompeu Fabra University in Barcelona, noted, “We cannot simply prescribe antidepressants for their positive effects without considering this side effect.”
The most common type of antidepressants are selective serotonin reuptake inhibitors (SSRIs). Their side effects can include weight gain. SSRIs work by increasing levels of serotonin, a neurotransmitter that helps regulate mood.
While modern antidepressants cause fewer side effects and work better than older drugs, they still carry downsides both immediately and over time. Common negative effects include sleep and digestive problems, dizziness, sexual dysfunction, and weight gain.
What Did the Researchers Discover?
The study followed 6,352 adults from northeastern Spain, ages 35 to 79, over six years.
Participants were divided into four groups based on antidepressant use: people who had never taken them, people who started them during the study, people who stopped taking them, and people who had been using them for a long time.
Throughout the study, nurses recorded participants’ weight, diet, exercise frequency, depressive symptoms, smoking status, diabetes status, and blood pressure.
The researchers focused on changes in body mass, especially new cases of obesity defined as a body mass index (BMI) of 30 or higher. All participants gained weight over the study period, but people who had used antidepressants long term gained more.
On average, people who had never taken antidepressants gained 0.8 percent of their body weight. Those who stopped taking them gained 2.2 percent, those who started during the study gained 2.5 percent, and long-term users gained 1.7 percent—about twice as much as people who never took them, reported the Daily Mail.
Dr. Camille Lassalle, a researcher at the Del Mar Hospital Research Institute, said, “All individuals who took antidepressants had a high likelihood of gaining weight and developing obesity. However, this risk is higher for those who take these medications continuously.”
Experts aren’t sure exactly why antidepressants lead to weight gain, but serotonin appears to be the common factor. Most antidepressants alter serotonin levels in the brain, which regulate mood and emotions.
SSRIs block the reuptake of serotonin, leaving more of the neurotransmitter available in the brain. Serotonin also helps regulate appetite, so changing its levels can affect eating behavior.
After people start SSRIs, brain serotonin levels rise, which can reduce impulsivity and increase feelings of fullness, causing them to eat less. However, after about a year on the medication the brain adapts. Receptors that respond to serotonin become downregulated, producing a kind of resistance. That shift can trigger cravings for quick energy sources like carbohydrates or sweets; those foods briefly boost serotonin but can lead to weight gain over time.
Doctors warn against stopping antidepressants abruptly without talking to a physician. Typically, clinicians recommend tapering the medication gradually over several weeks because sudden withdrawal can cause severe symptoms, including dizziness, mood swings, sleep problems, and “brain zaps,” which feel like electric shocks in the head.
The study’s findings were published in the journal Frontiers in Psychiatry.
