Does Prozac (Fluoxetine) Cause Weight Gain? Everything You Need to Know

Do Antidepressants Cause Weight Gain?

The answer to the question, “Do antidepressants cause weight gain?” is: “Maybe.” In the official list of side effects and adverse reactions triggered by Prozac (fluoxetine), the material mentions both weight loss and decreased appetite, which implies that people stand a greater risk of losing weight on Prozac than gaining it.¹ This appears to be true for children and adults.

Although the information on Prozac actually suggests a decrease in weight, antidepressants as a group are linked to weight gain. In fact, aside from nausea, sleepiness, and sexual problems, weight gain is one of the most common side effects of antidepressants overall.²

A study that tracked Prozac use for one year found that patients tended to lose some weight in the first four weeks of treatment. After that initial loss, the weight gained was the same for people who took Prozac and people who took a placebo, which means Prozac had no significant impact on weight gain.⁴

There are various reports as to how prevalent weight gain is in regards to taking Prozac and other SSRIs. Different studies report that the percent of patients with significant weight gain to be somewhere between 10-25 percent. I would say that from my clinical experience using SSRIs most people do not have weight gain as a significant problem or reason to stop the medication. I would estimate that in my practice, less than 10 percent of people complain about weight gain as a reason to stop the medication. I have noticed that if someone had a problem with weight prior to getting on medication or has a strong family history of obesity or metabolic syndrome the risk is higher. The risk may also be higher at higher doses of medication,” says Dr. Alex Anastasiou, a board-certified psychiatrist in California.

Why Do Antidepressants Cause Weight Gain?

Certainly many medications, including antidepressants, can cause weight gain. By understanding the impact of medications on a person’s desire to eat and their body’s ability to process food, one can learn ways to manage the changes.

Experts point to four possible reasons why antidepressants may cause weight gain:⁴

1. Appetite May Improve as Symptoms Improve

Unintentional changes in appetite and weight are common symptoms of depression and other mental health disorders. Some people overeat and gain weight when they are depressed, and others are too depressed or anxious to eat. These people will see weight loss as a sign their condition is worsening.

When these people start treatment with an antidepressant, they could see some of their weight return. To them, this weight gain should be a welcomed indication of improvement and not a cause of concern.

2. Certain Medications May Cause Food Cravings

Medications for depression and other mental health disorders can trigger powerful urges for certain foods or drinks. Perhaps, the new antidepressant makes the person crave salty snacks, fatty foods, and sugary drinks. As consumption of these items increases with the urges, there will likely be weight gain. Unless these cravings are curbed, the weight gain could continue throughout the course of treatment.

3. Medications May Change the Experience of Being Full

Experts suspect that the communication between the stomach and the brain could be disrupted by psychiatric medications. Rather than sending a message from the stomach to tell the brain to stop eating, this signal could be delayed or absent. Not only would this lead to a person gaining weight in the long-term, but in the short-term they could also be uncomfortably full and ill.

4. Medications May Slow Metabolism

A person’s metabolism dictates the way the body processes and uses food for energy. If a medication slows metabolism, it will burn calories at a different rate, leading to weight gain over time. A slowed metabolism could also be linked to less energy and motivation to engage in healthy activities.

Which SSRIs Cause Weight Gain?

SSRIs and other antidepressants may cause weight gain in some people, so it may be helpful to know which ones are linked to the greatest risk. It’s also important to consider that adults tend to gain weight as they age, so just because someone weighs more over time does not mean the antidepressant is a contributing factor.

One study found common SSRI antidepressants that may cause weight gain include the following:^5,6

• Citalopram (Celexa): showed the greatest steady gain of the medications studied with increases of 2% body weight after 12 months
• Paroxetine (Paxil): showed an increase in weight over the first nine months before leveling off under 2% of total body weight change
• Escitalopram (Lexapro) and Sertraline (Zoloft): each of these medications seem to trigger a weight gain over the first 9 months followed by some weight loss approaching 12 months after initiation

Fluoxetine was the only SSRI from the study that failed to trigger a similar weight change. Over the course of the study, the weight change from Prozac was about half of the other medications surveyed. Of course, everyone reacts differently to SSRIs, so one person’s experience could be much different than the average.

Other medications shown to cause higher increases in weight include:⁶

• Tricyclic antidepressants: including amitriptyline, imipramine, and doxepin
• Phenelzine (Nardil): a certain monoamine oxidase inhibitor (MAOI)
• Mirtazapine (Remeron): an atypical antidepressant

Other medications were linked to no weight gain at all, or a weight gain that was followed by a period of weight loss. Bupropion (Wellbutrin) seems to create very little impact on weight. People may notice a slight weight loss three months after starting the medication, but they are likely to return to their starting weight 12 months after treatment.⁵

Another antidepressant, duloxetine (Cymbalta), shows a different impact on weight. Weight seems to remain stable after three months, followed by a significant gain at months six and nine, then a decrease between month nine and 12. After a year of treatment, the person will be near their baseline weight with little noticeable change.⁵

Impacts of Short-Term vs. Long-Term Use On Weight Gain

Any medication change or adjustment to a person’s mental health is bound to impact weight in one direction or the other. Prozac, however, seems to have little influence on weight overall. In the short-term, a person could report losing a few pounds. In the long term, they could see the scale creep a little higher, but this gain will be minor in most cases.⁵

Ways to Manage Prozac Weight Gain

In the rare case that someone is affected by Prozac weight gain, they can take steps to lessen the unwanted outcomes. First and foremost, they should talk to their doctor or prescriber about what they have noticed since starting the medication to determine if the side effects outweigh the benefits. From there, it will be time to take action and determine healthy options.

Six ways to manage fluoxetine weight gain include:⁶

1. Adjust doses: not everyone will take or need the same dose of Prozac. Perhaps, a higher or lower dose creates more side effects, so trying a different level could end with less weight gain.
2. Switch drugs: Prozac may not be the best drug for someone if weight gain is a side effect. With the variety and accessibility of antidepressants, there could be a better option.
3. Change diet and eating habits: so much of weight gain boils down to what and how much a person is eating. Consider adjusting your diet to add healthier foods and avoid sugary drinks.
4. Increase exercise: boosting your physical activity can help burn some calories and build some muscle to manage weight. Plus, exercise has a tremendously positive impact on your mental health.
5. Work with a dietician to manage caloric intake/nutrition: each person has unique needs when it comes to nutrition and finding helpful options can be a challenge. Seeking professional assistance can help fastrack weight management.
6. Accept the changes: no one is thrilled about gaining weight, but a few pounds here and there should not drastically impact a person’s self-esteem. Finding ways to accept and embrace the weight gain from medications is a great way to support mental health.

Final Thoughts On Prozac Weight Gain

Someone who is concerned about starting a new medication because of the possible effect on weight should feel fairly confident using Prozac. If you’re unhappy with the side effects you’re feeling from Prozac or any other antidepressant, discuss other options with your doctor. In all likelihood, there is a medication that offers all of the same benefits with fewer side effects.