Dozens of commonly prescribed medications can cause weight gain, and roughly one in five U.S. adults takes at least one of them. The biggest culprits fall into a handful of drug classes: psychiatric medications (antipsychotics, antidepressants, mood stabilizers), diabetes drugs, corticosteroids like prednisone, beta-blockers for blood pressure, and certain seizure medications. The amount of weight gained varies widely, from a couple of pounds to 15 or more, depending on the drug, the dose, and how long you take it.
Antipsychotics
Antipsychotics are the most potent weight-gain drugs pound for pound, even though only about 1% of adults use them. Second-generation (newer) antipsychotics are the worst offenders. In a large analysis published in The Lancet Psychiatry, clozapine caused an average weight gain of about 3 kg (6.6 lbs) more than placebo, and olanzapine was close behind. Some patients gain considerably more than the average. Older antipsychotics like haloperidol barely moved the scale.
The reason these drugs pack on weight comes down to how they interact with the brain. Antipsychotics that strongly block histamine receptors and certain serotonin receptors tend to ramp up appetite. They also interfere with dopamine signaling in ways that reduce insulin sensitivity, meaning your body has a harder time processing sugar normally. The combination of eating more and metabolizing fuel less efficiently creates a perfect storm for weight gain, and it often starts within the first few weeks of treatment.
Antidepressants
Most antidepressants cause some weight gain, but the differences between them are smaller than many people expect. In a large study tracked by Harvard Health, researchers used citalopram (Celexa) as a benchmark because it sits in the middle of the pack. People taking citalopram gained an average of one to two pounds. Most other antidepressants fell in a similar range.
Mirtazapine (Remeron) and paroxetine (Paxil) have long had reputations as the most likely to cause noticeable gain. Like antipsychotics, they work partly through histamine and serotonin pathways that stimulate appetite. On the other end of the spectrum, bupropion (Wellbutrin) stands out as essentially weight-neutral, with close to zero average gain. If weight is a major concern, bupropion is often considered as an alternative for that reason.
One important nuance: antidepressant-related weight gain tends to accumulate slowly over months or years rather than hitting all at once. That gradual creep can make it hard to recognize the medication as the cause, especially if your appetite and energy levels are also shifting as your mood improves.
Mood Stabilizers
Lithium and valproate (Depakote) are two of the most commonly prescribed mood stabilizers, and both carry significant weight gain risk. In one chart review study, patients on either drug gained an average of about 6.3 to 6.4 kg (roughly 14 lbs), with an average increase of about 8% over their starting body weight.
Lithium appears to act partly like insulin in the body, increasing glucose uptake into cells. It may also directly stimulate appetite through effects on the hypothalamus, the brain region that regulates hunger. Valproate, meanwhile, is linked to insulin resistance and metabolic disruption. For women, valproate carries the additional concern of being associated with polycystic ovary syndrome and abnormal cholesterol levels.
Diabetes Medications
This might sound counterintuitive, but several medications prescribed for type 2 diabetes actually promote weight gain. About 5.7% of U.S. adults take a diabetes drug classified as weight-promoting, making this the second most common category after beta-blockers.
Insulin therapy is the most familiar example. When insulin is combined with certain oral medications, the effect multiplies. In clinical studies, adding a drug from the thiazolidinedione class (like rosiglitazone or pioglitazone) to insulin led to gains of 4 to 5 kg (9 to 12 lbs) over six months. Part of this is fluid retention, and part is genuine fat accumulation. Sulfonylureas, another older class of diabetes pills, typically add 2 to 3 kg on their own.
Newer diabetes drugs tell a very different story. GLP-1 receptor agonists (the class that includes semaglutide) and SGLT2 inhibitors actually promote weight loss, which is one reason prescribing patterns have shifted heavily toward them in recent years.
Beta-Blockers
Beta-blockers are the single most common weight-promoting medication class in the U.S., used by nearly 10% of adults. These drugs, prescribed for high blood pressure, heart failure, and anxiety, slow your heart rate and reduce your body’s energy expenditure. That metabolic slowdown can translate into gradual weight gain.
The risk isn’t equal across all beta-blockers. Older options like atenolol (Tenormin) and metoprolol (Lopressor) are more likely to cause weight gain, and the gain tends to happen in the first few months before leveling off. Newer beta-blockers with vasodilating properties, such as carvedilol (Coreg) and nebivolol (Bystolic), don’t typically cause weight gain at all.
Corticosteroids
Prednisone and other corticosteroids are notorious for weight gain, especially at higher doses or when taken for more than a few weeks. The risk climbs steeply once the daily dose exceeds about 7.5 mg of prednisone. At that level, the body starts to experience a cascade of hormonal changes: increased appetite, impaired sugar metabolism, and a characteristic redistribution of fat to the face, abdomen, and upper back (sometimes called a “moon face” or “buffalo hump”).
Short courses of steroids, like a five-day burst for a bad asthma flare, rarely cause lasting weight changes. The trouble comes with chronic use for conditions like rheumatoid arthritis, lupus, or inflammatory bowel disease, where patients may need steroids for months or years. The appetite increase can be dramatic. Some people describe feeling hungry in a way that feels almost impossible to ignore.
Seizure Medications
Anticonvulsants are a mixed bag. Valproate, discussed above as a mood stabilizer, is also widely used for epilepsy, and its weight gain profile is one of the highest in this class. Gabapentin and pregabalin, frequently prescribed for nerve pain as well as seizures, also carry moderate weight gain risk.
On the flip side, topiramate (Topamax) and zonisamide tend to cause weight loss, which is why topiramate is actually an ingredient in some prescription weight-loss combinations. If you’re taking an anticonvulsant and concerned about weight, there may be alternatives within the same class that behave very differently on the scale.
Why These Drugs Cause Weight Gain
The mechanisms vary by drug class, but most medication-related weight gain traces back to one or both of two pathways: your brain’s appetite signals get turned up, or your body becomes less efficient at processing calories. Many psychiatric medications, for instance, block histamine receptors in the brain. Histamine normally helps suppress appetite, so blocking it makes you hungrier. Others interfere with serotonin signaling, which plays a role in feeling full after a meal.
The metabolic side is subtler but just as important. Drugs that reduce insulin sensitivity force your body to produce more insulin, which promotes fat storage. Some medications also lower your resting metabolic rate, meaning you burn fewer calories even at rest. Beta-blockers do this directly by reducing heart rate and dampening the body’s “fight or flight” response, which normally burns energy.
What You Can Do About It
The most effective first step is knowing which of your medications carries weight gain risk, because awareness alone changes behavior. If you notice a pattern of weight creeping up after starting a new prescription, that information is useful in a conversation with your prescriber about alternatives.
Switching medications is sometimes an option. Within most drug classes, there are lower-risk alternatives that work through different mechanisms. Among antipsychotics, for example, switching to a lower-risk option or simply reducing the dose has been shown to produce an average weight reduction of about 1.5 kg compared to staying on the same regimen. Among antidepressants, bupropion stands apart as weight-neutral. Among beta-blockers, newer vasodilating versions avoid the metabolic slowdown.
When switching isn’t possible, adding a second medication to counteract weight gain is another strategy. For people on antipsychotics, starting metformin (a diabetes drug that improves insulin sensitivity) at the same time has been shown to reduce weight gain by about 3 to 5 kg over the first year compared to taking the antipsychotic alone. Newer GLP-1 receptor agonists show even larger effects, reducing weight by an average of 6 kg in studies of antipsychotic-treated patients.
Diet and exercise matter here too, but they work best as part of a combined approach rather than the sole strategy. The appetite-stimulating effects of some medications can make willpower-based approaches feel like swimming against a current. Understanding that the hunger is pharmacologically driven, not a failure of discipline, is an important reframe for many people navigating this challenge.