Does Prozac Cause Weight Gain?

Katelyn Hagerty

Reviewed by Katelyn Hagerty, FNP

Written by Nicholas Gibson

Published 06/24/2022

Updated 06/25/2022

Prozac®, which contains the active ingredient fluoxetine, is an antidepressant that’s prescribed to treat major depressive disorder (MDD) and other mood disorders.

Used effectively, Prozac can help to improve your moods and reduce the severity of depression symptoms. However, many people prescribed Prozac have concerns about gaining weight while using this medication. 

Does Prozac cause weight gain? Like many other antidepressants, Prozac is often thought of as causing weight gain. However, research is mixed overall, and some studies suggest that Prozac may be more likely to cause weight loss than weight gain.

Below, we’ve covered what Prozac is, as well as how it works as a treatment for depression and other mental health disorders. We’ve also looked into the science on Prozac and weight gain to explain what you need to know if you’re considering using this medication.

Finally, we’ve shared some tips and techniques to help you maintain a healthy weight and eating habits while using Prozac.

Prozac is a brand name for fluoxetine, an antidepressant that’s part of a class of drugs referred to as selective serotonin reuptake inhibitors (SSRIs). It comes as a capsule and is available in standard and delayed-release formulations.

Prozac has been around since the mid-1980s. In fact, it was the first SSRI approved for use by the Food and Drug Administration (FDA), which allowed it to come onto the market in 1987. 

Fluoxetine, the active ingredient in Prozac, is currently approved by the FDA as a treatment for major depressive disorder, obsessive-compulsive disorder (OCD), panic disorder and bulimia nervosa.

Like other SSRIs, Prozac works by raising levels of the neurotransmitter serotonin in your brain and body.

Serotonin plays a major role in regulating your moods and feelings. Research suggests that low levels of serotonin are involved in the development of depression, anxiety, suicidal behavior and obsessive-compulsive disorder.

By increasing serotonin levels, Prozac can help to reduce the severity of depressive symptoms, which may make it easier for you to maintain mental balance.

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Many antidepressants can cause side effects, and Prozac is no exception. Although Prozac has a lower risk of causing adverse effects than older medications, it’s not uncommon to experience mild, transient side effects while using Prozac to treat depression or other conditions.  

Common side effects of Prozac include:

  • Nausea

  • Diarrhea

  • Asthenia (physical weakness)

  • Difficulty falling asleep or staying asleep

  • Feelings of nervousness and/or anxiety

  • Somnolence (drowsiness)

  • Dry mouth

  • Sweating

  • Tremor

Many of these potential side effects are similar to the general side effects of SSRIs, which also occur with other medications in this class. 

However, one side effect that’s much less common with Prozac than with other antidepressants is weight gain. 

If you’ve ever read about antidepressant side effects, you’ve likely seen increased appetite and weight gain near the top of the list. Many antidepressants are known for their effects on body weight, particularly older medications such as tricyclic antidepressants (TCAs).

This reputation is somewhat deserved, as many antidepressants can cause modest weight gain, but it’s not totally accurate when it comes to Prozac. 

Unlike other antidepressants, research largely suggests that Prozac is more likely to cause loss of appetite and a small decrease in weight than long-term weight gain. 

For example, a one-year clinical trial published in the American Journal of Psychiatry found that people who used fluoxetine, the active ingredient in Prozac, showed a modest degree of weight loss during treatment.

On average, the people that participated in the study lost around 0.9 pounds. None of the study participants withdrew from therapy because of weight loss caused by the treatment. 

Other research has produced similar findings. For example, a cross-sectional study published in the journal General Hospital Psychiatry in 2015 tracked more than 360 antidepressant users for six to 36 months to assess the effects of their medication on body weight.

The researchers found that the following antidepressants were associated with significant levels of weight gain:

Fluoxetine — the active ingredient in Prozac — was the only antidepressant in the study that was not associated with significant weight gain.

Because of its minimal effect on body weight, fluoxetine is occasionally called a “weight neutral” antidepressant. In general, its effects on appetite and body weight are relatively small, and it’s not associated with large amounts of weight gain or weight loss.

Although Prozac doesn’t have a significant effect on weight for most people, it’s still important to maintain healthy eating habits if you’re prescribed this medication.

You can help maintain a healthy weight while using Prozac by following these steps:

  • Checking your weight occasionally. If you’re worried about weight gain or weight loss while taking Prozac, try to check your weight on a weekly or monthly schedule. If you’ve lost or gained weight, it’s a good sign that it’s time to adjust your diet or activity level.

  • Monitoring your total food intake. While using Prozac, your body will still store energy as excess weight in your fat cells. Similarly, it will also burn away excess fat as a source of energy if you don’t eat enough.
    If your weight is changing unexpectedly, try to monitor your food intake for a week, then compare it to your basal metabolic rate. You may find that you’re accidentally eating too much or too little. 

  • Eating a healthy, balanced diet. The most effective way to maintain a stable weight is to eat a balanced diet. Try to prioritize fresh fruits, vegetables, lean protein sources and complex carbohydrates while minimizing your intake of salty or processed foods.

  • Being physically active. Try to keep yourself physically active, as even mild exercise can burn calories and help you to maintain your weight. Try to exercise for at least 150 minutes a week, even if it’s just a brisk walk or bike ride around your neighborhood.
    In addition to helping you maintain your weight, regular exercise can help to reduce the severity of depression by stimulating the release of natural, mood-enhancing chemicals called endorphins. 

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Prozac is one of the most effective, widely-used antidepressant medications for the treatment of depression. It’s used by people of all ages and backgrounds, with side effects typically mild and easy to deal with.

Does Prozac cause weight gain? Overall, research suggests that Prozac only has a mild impact on weight and body composition, even when it’s used as a long-term treatment for depression.

However, it’s important to keep in mind that the same rules of metabolic activity still apply when you’re using Prozac, meaning that if you get limited physical activity and eat above your normal food intake, you may start to gain weight.

If you’re prescribed Prozac and notice changes in your eating habits or body weight, it’s best to talk to your healthcare provider.

They’ll be able to help you manage your weight and stay healthy while you’re using Prozac for depression, obsessive-compulsive disorder or any other condition.

Interested in treating depression? We offer fluoxetine (the active ingredient in Prozac) as part of our range of depression and anxiety treatments, following an online consultation with a licensed psychiatry provider who will determine if a prescription is appropriate. 

You can also learn more about depression with our mental health services, or by accessing our free online mental health resources and content. 

8 Sources

Hims & Hers has strict sourcing guidelines to ensure our content is accurate and current. We rely on peer-reviewed studies, academic research institutions, and medical associations. We strive to use primary sources and refrain from using tertiary references.

  1. PROZAC (fluoxetine capsules) for oral use. (2017, January). Retrieved from
  2. Fluoxetine. (2022, January 15). Retrieved from
  3. Brain Hormones. (2022, January 23). Retrieved from
  4. Michelson, D., et al. (1999, August). Changes in weight during a 1-year trial of fluoxetine. The American Journal of Psychiatry. 156 (8), 1170-1176. Retrieved from
  5. Uguz, F., et al. (2015). Weight gain and associated factors in patients using newer antidepressant drugs. General Hospital Psychiatry. 37 (1), 46-48. Retrieved from
  6. Wharton, S., et al. (2018). Medications that cause weight gain and alternatives in Canada: a narrative review. Diabetes, Metabolic Syndrome and Obesity: Targets and Therapy. 11, 427-438. Retrieved from
  7. How much physical activity do adults need? (2022, March 17). Retrieved from
  8. Antidepressants and weight gain: What causes it? (n.d.). Mayo Clinic.

This article is for informational purposes only and does not constitute medical advice. The information contained herein is not a substitute for and should never be relied upon for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment. Learn more about our editorial standards here.

Katelyn Hagerty, FNP

Kate Hagerty is a board-certified Family Nurse Practitioner with over a decade of healthcare experience. She has worked in critical care, community health, and as a retail health provider.

She received her undergraduate degree in nursing from the University of Delaware and her master's degree from Thomas Jefferson University. You can find Katelyn on Doximity for more information.

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