There’s a lot of talk in the news lately about antidepressants and weight gain, so let’s look at some numbers.

Here’s a study from July 2024 that compared the weight gain of eight popular antidepressants, and pop-science outlets have reported it with such snippets as:

❝Bupropion users were approximately 15–20% less likely to gain a clinically significant amount of weight than those taking the most common medication, sertraline.

The researchers considered weight gain of 5% or more as clinically significant.❞

Read in full: Study compares weight gain across eight common antidepressants

At this point, you might (especially if you or a loved one is on sertraline) be grabbing a calculator and seeing what 5% of your weight is, and might be concerned at the implications.

However, this is a little like if, in our This or That section, we were to report that food A has 17x more potassium than food B, without mentioning that food A has 0.01mg/100g and food A has 0.17mg/100g, and thus that, while technically “17x more”, the difference is trivial.

As a quick aside: we do, by the way, try to note when things like that might skew the stats and either wipe them out by not mentioning that they contain potassium at all (as they barely do), or if it’s a bit more, describing them as being “approximately equal in potassium” or else draw attention to the “but the amounts are trivial in both cases”.

Back to the antidepressants: in fact, for those two antidepressants compared in that snippet, the truth is (when we go looking in the actual research paper and the data within):

• sertraline was associated with an average weight change of +1.5kg (just over 3lb) over the course of 24 months
• bupropion was associated with an average weight change of +0.5kg (just under 1lb) over the course of 24 months

Sertraline being the most weight-gain-inducing of the 8 drugs compared, and bupropion being the least, this means (with them both having fairly even curves):

• sertraline being associated with an average weight change of 0.06kg (about 2oz) per month
• bupropion being associated with an average weight change of 0.02kg (less than 1oz) per month

For all eight, see the chart here in the paper itself:

Medication-Induced Weight Change Across Common Antidepressant Treatments ← we’ve made the link go straight to the chart, for your convenience, but you can also read the whole paper there

While you’re there, you might also see that for some antidepressants, such as duloxetine, fluoxetine, and venlafaxine, there’s an initial weight gain, but then it clearly hits a plateau and weight ceases to change after a certain point, which is worth considering too, since “you’ll gain a little bit of weight and then stay at that weight” is a very different prognosis from “you’ll gain a bit of weight and keep gaining it forever until you die”.

But then again, consider this:

Most adults will gain half a kilo this year – and every year. Here’s how to stop “weight creep”

That’s more weight gain than one gets on sertraline, the most weight-gain-inducing antidepressant tested!

What about over longer-term use?

Here’s a more recent study (December 2024) that looked at antidepressant use over 6 years, and found an average 2% weight gain over those 6 years, but it didn’t break it down by antidepressant type, sadly:

Trajectories of antidepressant use and 6-year change in body weight: a prospective population-based cohort study

…which seems like quite a wasted opportunity, since some of the medications considered are very different, working on completely different systems (for example, SSRIs vs NDRIs, working on serotonin or norepinephrine+dopamine, respectively—see our Neurotransmitter Cheatsheet for more about those) and having often quite different side effects. Nevertheless, the study (despite collecting this information) didn’t then tabulate the data, and instead considered them all to be the same factor, “antidepressants”.

What this study did do that was useful was included a control group not on antidepressants so we know that on average:

• never-users of antidepressants gained an average of 1% of their bodyweight over those 6 years
• users-and-desisters of antidepressants gained an average of 1.8% of their bodyweight over those 6 years*
• continuing users of antidepressants gained an average of 2% of their bodyweight over those 6 years

*for this group, weight gain was a commonly cited reason for stopping taking the antidepressants in question

Writer’s anecdote: I’ve been on mirtazapine (a presynaptic alpha₂-adrenoreceptor antagonist which increases central noradrenergic and serotonergic neurotransmission) for some years and can only say that I wish I’d been on it decades previously. I requested mirtazapine specifically, because I’m me and I know my stuff and considered it would most likely be by far the best fit for me out of the options available. Starting at a low dose, the only meaningful side effect was mild sedation (expected, and associated only with low-dose use); increasing after a couple of weeks to a moderate dose, that side effect disappeared and now the only remaining side effect is a slight dryness of the mouth, which is fine, as it ensures I remember to stay hydrated 🙂 anyway, my weight hasn’t changed (beyond very small temporary fluctuations) in the time I’ve been on mirtazapine. Disclaimer: the plural of anecdote is not data, and I can only speak for my own experience, and am not making any particular recommendation here. Your personal physiology will be different from mine, and may respond well or badly to any given treatment according to your own physiology.

Further considerations

This is touched on in the “Discussion” section of the latter paper (so do check that out if you want all the details, more than we can reasonably put here), but there are other factors to consider, for example:

• whether people were underweight/healthy weight/overweight at baseline (sometimes, a weight gain can be a good thing, recovering from an illness, and in the case of the illness that is depression, weight can swing either way)
• antidepressants changing eating and exercise habits (generally speaking: more likely to eat more and exercise more)
• body composition! How did they not cover this (neither paper did)?! Muscle weighs more than fat, and improvements in exercise can result in an increase in muscle and thus an increase in overall weight.

As researchers like to say, “this highlights the need for more high-quality studies to look into…” (and then the various things that went unexamined).

Want to know more?

Check out our previous main feature:

Antidepressants: Personalization Is Key!

Take care!