Medications that affect weight
Weight that begins to increase without changes in diet or activity is sometimes explained not by metabolism, but by a medication started a couple of months prior. The list of such groups is well-known, and this should be discussed with the prescribing physician, not a food diary.
First things first
No medication listed below should be discontinued or changed on your own. Weight gain is a side effect, and the treatment was prescribed for a condition that carries more weight. The conversation should be structured differently: you inform your doctor about the weight gain, and they decide whether there is an alternative within the same class with a lesser effect.
Second: for most of these drugs, the link is established at the group level, but the magnitude for a specific individual is difficult to predict. The same drug may cause a five-kilogram gain in one person and zero in another.
Groups where weight gain is documented
| Group | Primary mechanism |
|---|---|
| Some antidepressants — tricyclics, mirtazapine, some SSRIs with long-term use | Increased appetite, carbohydrate cravings |
| Some antipsychotics — olanzapine, clozapine, and others | Appetite plus changes in carbohydrate and lipid metabolism |
| Some anticonvulsants — valproates, gabapentin, pregabalin | Appetite, less commonly fluid retention |
| Systemic glucocorticosteroids | Sodium and water retention, appetite, fat redistribution |
| Insulin and sulfonylurea drugs | Reduced glucose loss, episodes of hypoglycemia followed by eating |
| Some older-generation beta-blockers | Reduced energy expenditure and exercise tolerance |
| Hormonal contraceptives | Primarily fluid retention, rather than fat gain |
| First-generation antihistamines with long-term use | Appetite, drowsiness, and reduced activity |
The list is incomplete and is intentionally categorized by groups rather than a list of brand names: drugs differ within the same group, and matching your specific medication to the correct row is the doctor's job.
Three different types of weight gain
It is useful to distinguish between them because they look different and resolve in different ways.
Fluid retention. Appears quickly — within days — and is accompanied by facial and leg swelling, and disappears just as quickly after discontinuation. This is not fat, and a calorie deficit does not affect it. It is typical for steroids and contraceptives.
Increased appetite. Grows gradually over months and looks like normal weight gain on the scale — because that is exactly what it is. Here, counting calories actually works, and it often turns out that 300–500 kcal more per day is being consumed than before starting the medication, despite the strong feeling that you are "eating the same as before."
Reduced energy expenditure. The most subtle variant: the food intake is the same, but movement is reduced due to fatigue, drowsiness, or decreased exercise tolerance. It is noticeable in the step count, not in a food diary.
What to do without stopping treatment
Record the fact and the timeline. The doctor needs two dates — the start of the medication and the start of the weight gain — and the amount. "I think I gained weight" and "plus six kilograms in four months since starting the medication" lead to different decisions.
Check if it is appetite or water. A week of tracking answers the question: if the average is noticeably higher than before, the issue is food. How to interpret this week is explained separately.
Focus on protein and food volume, not restrictions. With medication-induced appetite increase, the same principles apply as always: protein in every meal and foods with low energy density provide satiety for fewer calories. The mechanism is here.
Count steps. If energy expenditure has dropped, it is visible in the step count before it shows on the scale. Guidelines are available on how many steps are needed per day.
Do not prescribe yourself "fat burners" on top of your treatment. Some supplements interact with medications, and this is a case where self-medication has a price. What they do in the body is analyzed here.
What to ask your doctor
- Is there a drug within the same group with less impact on weight, and is it suitable for your case?
- Can the dose or the dosing schedule be adjusted?
- Is the weight gain in your case fluid or adipose tissue, and how can you tell the difference?
- Do you need to monitor glucose and lipids while taking the medication? For some groups, this is standard practice.
- Is the effect expected to be temporary? For a number of drugs, weight gain occurs in the first few months and then plateaus.
Medications that reduce weight
The flip side of the same topic. There are groups prescribed specifically for weight loss — GLP-1 receptor agonists and related drugs. They have their own nutritional specifics: with rapid weight loss on these, it is easy to lose muscle mass, and protein intake along with strength training become not just a recommendation, but part of the regimen. An analysis is available on nutrition while on weight loss medications.
And there are drugs that reduce weight as a side effect: metformin, topiramate, and some stimulants. This is not a reason to request them for yourself — each has its own profile of indications and risks.
When it is not the medication after all
Before attributing weight gain to a medication, it is worth ruling out more common causes: a changed diet, reduced activity, lack of sleep, and medically, thyroid issues and insulin resistance. There is an analysis on the former, and here on the latter. And separately on the idea that your metabolism is "broken" — why this is most often not the case.
Frequently asked questions
- Which medications most often cause weight gain?
- Some antidepressants and antipsychotics, certain anticonvulsants, systemic glucocorticosteroids, insulin and sulfonylurea drugs, older generation beta-blockers, hormonal contraceptives, and first-generation antihistamines when taken long-term.
- Can I stop taking a medication if it is causing weight gain?
- Not on your own. The treatment was prescribed for a condition that outweighs the side effect. The decision to switch to a drug in the same class with less impact on weight must be made by the prescribing physician.
- How can I tell if the weight gain is water retention rather than fat?
- Fluid retention appears over a few days, is accompanied by facial and leg swelling, and does not respond to a calorie deficit. Weight gain due to increased appetite occurs over months and is visible in a food diary as an increase in average consumption.
Read next
- The thyroid gland and weight: what it explains and what it doesn't — The thyroid gland regulates metabolic rate, making it a convenient explanation for any weight gain.
- Nutrition while on weight loss medication: how to maintain muscle mass — In published observations, lean tissue accounted for between one-quarter and forty percent of total weight lost.
- Metabolism: is it true that it can be "boosted" and that it can "break" — One person is promised a metabolism boost through spices and frequent small meals, another explains weight plateaus by claiming their metabolism is broken from dieting.
This article is for general information. It is not medical advice, a diagnosis, or a prescription for treatment or a diet, and it does not replace a consultation with your doctor. If you have a health condition, are pregnant, take medication, or follow a diet prescribed to you, decisions about food belong with your doctor.
Figures from regulations, guidelines and studies are given as they stood when this article was prepared and may since have changed; check them against the primary sources. This article is not advertising, an offer, or individual advice, and neither the author nor the site owner is responsible for decisions taken on the basis of it.