Weight gain is one of the most common reasons people quit antidepressants on their own. It is also one of the most preventable, because the drugs differ far more than most people realize.
The short answer
Some antidepressants block brain receptors that regulate appetite, which increases hunger and cravings. The risk is highest with mirtazapine, paroxetine, and amitriptyline. It is lowest with bupropion, which is linked to modest weight loss.
The largest head-to-head comparison, a 2024 study in Annals of Internal Medicine of 183,118 adults, found bupropion caused the least weight gain of eight first-line antidepressants. Sertraline and fluoxetine sat in the middle. Escitalopram, paroxetine, and duloxetine caused the most.
The average differences are small, under half a kilogram at 6 months. But averages hide the people at the tails, and for a meaningful minority the gain is large enough to matter.
Why do antidepressants change your weight?
No single mechanism explains it. Three contribute, in different amounts for different drugs.
Histamine H1 receptor blockade. Some antidepressants are potent antihistamines in the brain. Blocking H1 receptors causes sedation and increased appetite. Mirtazapine is the clearest example: it is one of the strongest H1 blockers in psychiatry, per the NIH StatPearls pharmacology review. Older tricyclics such as amitriptyline share this property.
Serotonin receptor effects. Serotonin signaling helps regulate satiety, the feeling of fullness after eating. Drugs that block certain serotonin receptors, including the 5-HT2C receptor, can increase food intake and carbohydrate cravings. This adds to the H1 effect for mirtazapine and helps explain why SSRIs, which do not block H1, still differ from each other.
Recovery itself. Depression often suppresses appetite. When treatment works, appetite returns. Some of the weight gained in the first months of treatment is the reversal of illness-related weight loss, not a drug side effect at all.
Which antidepressants cause the most weight gain?
A 2010 meta-analysis in the Journal of Clinical Psychiatry by Serretti and Mandelli reviewed the full body of trial evidence. Three drugs stood out for weight gain:
- Amitriptyline, an older tricyclic antidepressant
- Mirtazapine, an atypical antidepressant often chosen when insomnia or poor appetite are prominent
- Paroxetine, the SSRI most consistently linked to weight gain in its class
The FDA label for mirtazapine puts numbers on it. In controlled trials, 17% of patients reported increased appetite, versus 2% on placebo. Weight gain of 7% or more of body weight occurred in 7.5% of patients, versus 0% on placebo.
Mirtazapine's appetite effect is not always unwanted. Prescribers sometimes select it on purpose for patients whose depression has caused severe appetite loss and sleeplessness. Its sedation is also why it appears often in discussions of depression with insomnia. The same properties become a liability for patients trying to avoid weight gain.
Which antidepressants cause the least weight gain?
Bupropion is the consistent answer across decades of evidence. The 2010 meta-analysis found it was associated with weight loss rather than gain. The 2024 Annals study confirmed it in modern real-world data: bupropion users gained 0.22 kg less than sertraline users at 6 months and were 15% less likely to gain 5% or more of their starting weight.
Fluoxetine is close behind. It showed no difference from sertraline at 6 months in the 2024 study, and the older evidence links it to mild weight loss during acute treatment, though that effect fades with longer use.
Sertraline served as the reference drug in the 2024 comparison and sat near the low end of the range.
One caution: bupropion is not right for everyone. Per NIH MedlinePlus, it carries seizure risk and is not used in people with seizure disorders or current or past eating disorders. It also works differently from SSRIs, which affects the fit for anxiety symptoms. Our Wellbutrin vs. Lexapro comparison covers that trade-off in detail.
How large is the difference in practice?
The 2024 study followed patients from eight US health systems for up to 24 months. The 6-month findings, with sertraline as the reference:
- Escitalopram, paroxetine, duloxetine: roughly 0.3 to 0.4 kg more gain on average, and 10% to 15% more likely to gain at least 5% of baseline weight
- Venlafaxine and citalopram: modestly more gain than sertraline
- Fluoxetine: no meaningful difference
- Bupropion: 0.22 kg less gain, 15% less likely to cross the 5% threshold
Two readings of these numbers are both correct. The average differences are small, a fraction of a kilogram, so weight should rarely be the only factor in choosing a drug. And the 5%-of-body-weight statistic shows real divergence at the individual level: for a 90 kg person, that threshold is 4.5 kg, and meaningfully more people crossed it on escitalopram or paroxetine than on sertraline or bupropion.
For a broader look at how the drug classes compare on efficacy and other side effects, see our antidepressant medication guide.
Is it the drug or the depression?
Worth asking before blaming the prescription. Depression itself changes appetite and weight in both directions; the National Institute of Mental Health lists appetite and unplanned weight changes among core symptoms.
Three patterns help separate the causes:
- Weight regained in the first weeks after appetite returns often reflects recovery, especially if the depression had suppressed eating.
- New, persistent hunger and cravings that begin with the medication and continue past remission point toward a drug effect.
- Gradual gain over many months on a higher-risk drug fits the pattern seen in the long-term studies, where drug differences became clearer with time.
What can you do if you gain weight on an antidepressant?
The one thing not to do is stop abruptly. Sudden discontinuation risks withdrawal symptoms and relapse; our guide to what happens when you stop taking antidepressants explains why the exit needs a plan.
Options a prescriber can work through with you:
- Weigh in early and track. Most drug-related gain builds gradually. Catching a trend at month two beats discovering it at month twelve.
- Give recovery-related gain time. If the gain restored pre-illness weight, it may plateau on its own.
- Address diet and activity first. Medication raises appetite; it does not add calories by itself. Structured support helps some patients offset the effect.
- Discuss a planned switch. If the gain continues and bothers you, moving to a more weight-neutral option such as bupropion, fluoxetine, or sertraline is a common, evidence-supported step, done as a managed cross-taper rather than a cold stop.
A medication that treats your depression and gets abandoned over a preventable side effect helps no one. The goal is a drug you can stay on.
Questions for your prescriber
- Where does my current medication sit on the weight-gain spectrum?
- Is my weight change more likely recovery or drug effect, given where my appetite was before treatment?
- At what point would we consider switching, and to what?
- If we switch, what does the cross-taper look like?
- Are there reasons bupropion would not be safe for me?
Last updated: August 2026. This article is for informational purposes only and does not constitute medical advice. Never stop or change an antidepressant without speaking to your prescriber. If you are in crisis, call or text 988 (Suicide & Crisis Lifeline) or go to your nearest emergency room.