Written by Christina Aungst, PharmD | Reviewed by Joshua Murdock, PharmD, BCBBS
Updated on January 31, 2023
Key takeaways:
Some commonly prescribed medications can cause weight gain. Both prescription and over-the-counter medications have been linked to this side effect.
Certain diabetes medications, antidepressants, and antipsychotics are medications that can cause weight gain. Antihistamines, some hormonal birth control methods, and sleep medications can also have this effect.
If you gain weight from your medications, switching medications may be an option you and your healthcare provider can discuss. A healthy diet and regular exercise may also help.
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Obesity is a growing concern in the U.S., affecting over 40% of adults as of 2020. Obesity can raise the risk for heart disease, Type 2 diabetes, and some cancers. People who are at heavier weights also have a higher risk of these health issues.
Weight gain can have multiple causes. But one that may not be initially thought of is medications. And while weight gain is a possible side effect for many medications, there are some that are more likely to cause it.
8 medications that cause weight gain
Many medications can cause weight gain. We’ll discuss eight of the biggest culprits below, as well as ways to manage this side effect. But keep in mind that these aren’t the only medications that may cause weight gain.
Some diabetes medications
There are multiple medications available to help treat diabetes. However, some diabetes medications can cause weight gain, including:
Insulin
Sulfonylureas like glipizide
Glitazones like pioglitazone (Actos)
Glinides like repaglinide
These medications cause your cells to absorb more glucose (sugar) from your blood. Your cells then change that extra glucose into fat. These medications typically cause about 5 lbs to 10 lbs of weight gain. The specific amount varies by medication.
Antidepressants or mood stabilizers
Some antidepressants and mood stabilizers are known to cause weight gain, such as:
Tricyclic antidepressants (TCAs) like amitriptyline and nortriptyline (Pamelor)
Mirtazapine (Remeron)
Some selective serotonin reuptake inhibitors (SSRIs), such as paroxetine (Paxil)
Lithium (Lithobid)
Experts aren’t entirely sure why some medications in this group cause weight gain. And the amount of weight people gain seems to vary between studies. So it’s hard to say how much weight you might gain with these medications.
For instance, some studies have found people taking amitriptyline gained anywhere from about 1 lb to 16 lbs. Lithium has been noted to cause a gain of as little as 2 lbs and as much as 22 lbs. Everyone’s experience with antidepressants and weight gain is unique. So be sure to discuss your treatment goals and concerns with your healthcare provider.
Antipsychotics like olanzapine
Antipsychotic medications may be prescribed for people living with conditions like schizophrenia, bipolar disorder, or depression. Weight gain is a known side effect for many of these medications. But some antipsychotics have little to no effect on body weight.
Some antipsychotics that are more likely to cause weight gain include:
Clozapine (Clozaril)
Olanzapine (Zyprexa)
Quetiapine (Seroquel)
Risperidone (Risperdal)
These medications also affect other aspects of your metabolism. They can make you feel hungrier, raise your cholesterol, and prevent your body from breaking down blood glucose efficiently. This can raise the risk of other long-term health conditions like Type 2 diabetes.
Anticonvulsants like gabapentin
Anticonvulsants can help treat seizure conditions and bipolar disorder. Some of them can also help prevent migraines and manage nerve pain. But some anticonvulsants can cause weight gain, including:
Gabapentin (Neurontin)
Pregabalin (Lyrica)
Carbamazepine (Tegretol, Equetro)
Valproate (Depakene, Depakote)
It’s not clear why medications like gabapentin cause weight gain, but it could be due to increased appetite. It’s important to keep in mind that not all anticonvulsants cause weight gain. Some, like lamotrigine (Lamictal), usually have no effect on body weight. And others, like topiramate (Topamax), can actually cause weight loss.
Antihistamines like Benadryl
Antihistamines are most often used to treat allergy symptoms. There’s some evidence that antihistamines may cause weight gain. But more research is needed to confirm if certain ones have a greater risk of this side effect than others.
Examples of antihistamines that may cause weight gain include:
Cyproheptadine
Hydroxyzine (Vistaril)
Diphenhydramine (Benadryl)
It’s thought that some antihistamines may cause weight gain by making you feel hungrier. Older antihistamines, like diphenhydramine, can cause drowsiness, which may make you less active.
Some beta blockers like metoprolol
Many beta blockers are often prescribed for heart failure and abnormal heart rhythms. Not all beta blockers cause weight gain. The ones most likely to cause this side effect are:
Atenolol (Tenormin)
Metoprolol (Lopressor, Toprol XL)
Propranolol
Experts believe these beta blockers may slow your metabolism. They can also make it harder to exercise. These two factors may explain why metoprolol and other beta blockers cause weight gain.
Weight gain with beta blockers typically happens during the first few months of treatment. It should taper off once your body adjusts to the medication.
For most beta blockers, the average weight gain is about 2 lbs to 3 lbs. But some may cause more weight gain than others. Metoprolol and propranolol are reported to cause weight gain of up to about 5 lbs. Atenolol may cause a bit more weight gain — up to 7.5 lbs.
Corticosteroids like prednisone
Corticosteroids (“steroids”) like prednisone can help lower inflammation. One of their long-term side effects is weight gain. Prednisone and other steroids mimic a hormone in the body called cortisol. Experts believe this stimulates appetite and changes the way the body processes fats and sugars. Steroids can also cause fluid build-up, which can contribute to weight gain.
Generally, most people take steroids for a short time. Weight gain shouldn’t be an issue with short-term use. It’s also not an issue with topical steroids, such as creams or eye drops. But some people may need to take steroids long term for certain inflammatory conditions. And this is when weight gain becomes more likely.
The birth control shot
Many people think that hormonal birth control causes weight gain. But for the most part, this is unlikely. Most of the weight gain from birth control is caused by water retention and bloating that happens when you first start it. This should go away as you adjust to the birth control method.
But there is one exception: the birth control shot. Depo-Provera (medroxyprogesterone) can cause weight gain. One study found that the shot caused an average weight gain of over 20 lbs after using the shot for 18 months. The medication’s labeling states that almost 38% of women in clinical trials gained more than 10 lbs after using the birth control shot for 2 years.
Does Ambien or melatonin cause weight gain?
No. Popular prescription sleeping medications like Ambien (zolpidem) don’t directly cause weight gain. But Ambien can cause some people to perform actions while sleeping, like sleepwalking. These actions could, in theory, include sleep eating. And extra eating could lead to weight gain. But reports of this side effect are extremely rare and unlikely to be the cause of weight gain for most people.
Melatonin doesn’t seem to cause weight gain either. In fact, some researchers think it could help prevent weight gain from some medications or promote weight loss. But the studies that have been conducted were either very small or were animal studies. More research is needed to confirm melatonin’s potential association with weight.
Keep in mind that many over-the-counter sleep aids contain an antihistamine, such as ZzzQuil (diphenhydramine) and Unisom (doxylamine). And as discussed above, antihistamines may cause weight gain.
Can weight gain caused by medications lead to long-term health issues?
Yes. Some of the medications above, such as certain antipsychotics and the birth control shot, can lead to significant weight gain for some people. And as mentioned earlier, people with overweight or obesity have a higher risk of long-term health conditions, such as Type 2 diabetes. So it’s important to discuss the best ways to lower your risks with your healthcare provider.
How can I manage weight gain from medications?
There are options to help manage weight gain caused by medications. Lifestyle changes, such as following a healthy diet and regularly exercising, may help. Your healthcare provider may also suggest weight loss medications if diet and exercise aren’t helping enough.
Switching medications to an alternative with a lower weight gain risk might also be an option. This may not be appropriate for everyone, especially if your current medication is working well for you. But it’s worth discussing with your healthcare provider.
When should I talk to my provider about weight gain from medications?
If you’re experiencing weight gain that feels uncomfortable or too bothersome for you, speak with your healthcare provider. A healthy and comfortable weight is different for everyone. And it never hurts to speak with your provider about it.
If you ever notice rapid weight gain, contact your healthcare provider. Weight gain from medications is typically more gradual, happening over weeks or months. Rapid weight gain could indicate a more serious problem, such as worsening heart failure.
The bottom line
Several medications can cause weight gain. Certain diabetes medications, antidepressants, and antipsychotics are common culprits. Steroids, the birth control shot, and some beta blockers can also cause weight gain. Lifestyle changes, like diet and exercise, may be helpful in managing this side effect. If you’re concerned about gaining weight from your medications, talk to your healthcare provider.
References
American Heart Association. (2017). Managing heart failure symptoms.
Amphastar Pharmaceuticals, Inc. (2022). Medroxyprogesterone acetate [package insert].
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