Will Prozac Cause Weight Gain? What Studies and People Report
Prozac is less tied to weight gain than many antidepressants, and early on some people's weight drops a little.
By withClaro Editorial · 2026-11-02 · 4 min read
Clinical section reviewed by Dr. Jason Tan , Consultant Psychiatrist, on October 27, 2026.
Key takeaways In Prozac's depression trials, decreased appetite and weight loss were more common than on placebo. A 2024 study of 183,118 people found weight change on fluoxetine about the same as on sertraline; the differences between antidepressants were under a pound at six months, with bupropion lowest. On r/prozac, about as many people said they lost weight as said they gained it, but those who gained reported larger changes. Raise a steady change in either direction with your prescriber, and do not stop Prozac on your own to control weight. On this page
What 266 people on r/prozac said about their weight Why can Prozac cause weight loss at first? Why can Prozac cause weight gain? Does Prozac cause weight gain in the long run? What can you do if your weight changes on Prozac? Prozac (fluoxetine) can cause weight gain for some people. In a large 2024 comparison of eight antidepressants, only bupropion was linked to less gain, and the differences were under a pound. Early on, some people's weight drops a little. In the FDA trials, more people on Prozac than on placebo had a smaller appetite and lost a little weight. Larger, longer studies found small differences, and people's own stories run both ways.
What 266 people on r/prozac said about their weight
We read 100 recent threads about weight on r/prozac, comments included, and 326 people described their own experience. Studies weigh people; here people describe what happened to them, and those with a change to report post more, so treat this as a range of experiences. Of the 326, 266 said whether their weight changed on Prozac, and gain and loss came up almost equally often:
What people reported Of 266 people Gained weight 108 Lost weight 107 No change 41 Lost at first, then gained, or the other way round 10
They were not the same size. Of the 108 who gained, 62 gave a number, typically about 21 pounds; of the 107 who lost, 50 did, typically about 12. So the direction is hard to predict, and a gain, when it happens, tends to be larger.
One person on r/prozac wrote:
It has been completely weight neutral for me.
Another saw it shift over time:
I originally lost 10 lbs on it, but then once I adjusted to the med, I went back to where I was.
Why can Prozac cause weight loss at first?
Because it can reduce appetite. In the depression trials behind the label, 11% of adults on Prozac reported decreased appetite, against 2% on placebo, and 1.4% lost weight, against 0.5%. In the OCD trials, decreased appetite affected 17%, against 10%. The label adds that only rarely did people stop Prozac because of it, but it also warns that significant weight loss can be harmful, especially for people who are underweight or have bulimia. Weight loss that keeps going is worth raising with your prescriber, particularly if you have had an eating disorder.
Why can Prozac cause weight gain?
The exact reasons aren't known, and they likely differ from person to person. On r/prozac, of 46 people who gained and said why, 24 named a bigger appetite or cravings, while 17 said their eating had not changed. One wrote:
My eating habits did not change and I’ve gained 20 pounds.
Does Prozac cause weight gain in the long run?
At six months, fluoxetine looks about the same as sertraline. A 2024 US study of 183,118 people compared weight six months after starting one of eight common antidepressants. Escitalopram, paroxetine and duloxetine were linked to slightly more gain, about 0.3 to 0.4 kg (under a pound) more, and bupropion to slightly less. Looked at another way, escitalopram, paroxetine and duloxetine carried a 10% to 15% higher chance of gaining at least 5% of body weight, and bupropion a 15% lower chance. The authors call these small differences, and only 28% to 41% of people were still taking their medicine at six months. For fluoxetine on its own, there is little data beyond that.
Over years, the data cover antidepressants as a group. A 2018 UK study of nearly 295,000 people found that gaining at least 5% of body weight happened at 11.2 per 100 person-years in people prescribed antidepressants, against 8.1 in those who were not, and the higher rate lasted at least six years. The authors note this is an association, not proof that the medicines caused it.
How Prozac compares with other SSRIs on side effects in general is covered in Prozac side effects .
What can you do if your weight changes on Prozac? Medically reviewed by Dr. Jason Tan on October 27, 2026, this section only.
What to do depends on which way your weight is moving and how fast, and it is a conversation with your prescriber rather than a reason to stop Prozac on your own; what stopping can feel like is covered in Prozac withdrawal . The clinical view:
Weight can change on an antidepressant, and noticing a change early gives you the most options.
In the first weeks, some people lose a little weight because of nausea or a smaller appetite. Gain, when it happens, usually builds over months, though with a few medications it can start within weeks. It varies a lot between people on the same medication.
Several things feed into it: appetite returning as mood improves, cravings, less activity, poor sleep and the medication itself.
What you can do:
- Mention a steady rise at your next appointment, while the change is still small. - Raise weight loss that keeps going, or an appetite that has not come back after the first weeks. ## What should you tell your prescriber about weight changes?
Tell your prescriber what changed, when it started and how much it bothers you, and ask what the options are for you, since the right one depends on your history. It helps to tell them:
When you started Prozac, your dose and any dose changes. When you first noticed a change, and whether it's still going. Changes in appetite, energy or sleep since starting. Whether your clothes fit differently. How much the change bothers you. Download on the App Store Weight changes on Prozac build slowly and can run either way. The withClaro app lets you log appetite, energy, sleep and mood each day, linked to your dose, and turns it into a report for your prescriber.
Frequently asked questions Is Prozac weight neutral? On average it is close to neutral, but individual people still gain or lose: on r/prozac, gain and loss were reported about equally often. Watch for changes in either direction.
Which antidepressant is least likely to cause weight gain? In the 2024 study, bupropion was linked to the least gain of the eight compared, and fluoxetine was close to sertraline. The differences were small, so other factors usually matter more in the choice.
Is Prozac better than Lexapro for weight? In the 2024 study, escitalopram was linked to slightly more gain than fluoxetine, about a pound on average. If weight matters to you, say so before your prescriber chooses a medication.
Will I lose the weight if I stop Prozac? Some people do, but the evidence is limited. Never stop Prozac on your own to change your weight; talk to your prescriber first.
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Sources Petimar J, et al. Medication-induced weight change across common antidepressant treatments: a target trial emulation study. Annals of Internal Medicine, 2024 PROZAC (fluoxetine) prescribing information, US Food and Drug Administration via DailyMed Gafoor R, Booth HP, Gulliford MC. Antidepressant utilisation and incidence of weight gain during 10 years' follow-up: population based cohort study. BMJ, 2018 Claro articles are for self-monitoring and educational purposes only. They are not a medical device, therapist, or diagnostic tool, and do not replace care from your prescribing clinician. If you are in crisis, contact your care team, emergency services, the Samaritans (UK: 116 123), or the Crisis Text Line (US: text HOME to 741741).