Fluoxetine does not usually cause significant weight gain, especially during the first few months of treatment. In the short term, it is more often linked to a small amount of weight loss or little change in weight.
With longer use, some people may gain weight, but studies suggest the average change is similar to what occurs with a placebo. This may happen as depression improves, appetite returns, and eating patterns become more regular, rather than because fluoxetine directly causes weight gain.
Individual responses can vary. Weight changes may depend on the dose, treatment duration, starting weight, lifestyle, and the condition being treated. Research showing weight loss often involved higher doses and people who were overweight or had obesity, so those findings may not apply to everyone taking fluoxetine for depression.
Do not stop fluoxetine or change the dose without medical guidance, since suddenly changing treatment can affect symptoms. Speak with the prescribing doctor if weight gain is noticeable, continues over time, or is causing concern.