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6 Most Common Drugs That Cause Weight Gain

By Charlie Seltzer, MD / February 20, 2016

We seem to live in a prescription-happy society. Given the amount of patients that traditional doctors must see in a day, it is usually easier (read: quicker) to give a medicine than address the underlying cause.

Unfortunately, all drugs have side effects, and weight gain is common to many drugs.

Doctors often do not address this when prescribing medicine, despite weight gain being very troubling for the patient. This can be even more frustrating when other options exist that do not cause this nasty side effect.

Here is a list of commonly used drugs associated with weight gain:

1) Benadryl

Benadryl (Diphenhydramine) is an antihistamine, which is used for allergies and as a sleep aid. It is found in Tylenol PM. Histamine is a chemical crucial for regulating food intake, causing appetite suppression when it binds to a specific receptor in the brain. It may also increase the breakdown of fat.1 When the histamine receptor is blocked, its effect on appetite is decreased, leading to increased food intake and weight gain. A large review study found that people who used antihistamines had higher weights, waist circumferences, and insulin concentrations than those who did not.2

Alternatives: Ask your doctor about inhaled medications for allergies which are not generally associated with weight gain. If you have trouble sleeping, consider natural remedies and better sleep habits (i.e. no caffeine late in afternoon, no TV in bed room, etc.).

2) Antidepressants

The most widely prescribed antidepressants are from a class called SSRIs, or selective serotonin reuptake inhibitors. Simply, serotonin is thought to play a role in mood, and brain levels are low in many depressed patients. SSRIs allow serotonin to stay active longer, contributing to enhanced mood in many people. Serotonin is also well known to be an appetite suppressant, so it stands to reason that these drugs will help with weight loss. It turns out that the opposite is true. This paradoxical effect is not completely understood, though likely has to do with the complex interaction between serotonin and other appetite regulating mechanisms. Certain SSRIs, like Prozac, are associated with short term weight loss, though this is temporary and long-term data show a weight-neutral or weight gain effect.3

Alternatives: These should be discussed with your doctor.

3) Beta Blockers

These drugs are used to treat high blood pressure as well as certain heart conditions. While it is unclear exactly how these drugs contribute to weight gain, it is likely at least partially related to metabolic slowdown. One of the ways these drugs work is by slowing down the heart, which decreases exercise capacity. Additionally, they may cause fatigue, which will then lead to decreased activity and less caloric expenditure.

Alternatives: If you are taking a beta blocker for high blood pressure, discuss other medication options with your doctor.

4) Prednisone

A synthetic corticosteroid, prednisone has potent anti-inflammatory properties. It is used to treat asthma flares and allergic skin conditions, as well as certain autoimmune diseases and arthritis. Prednisone causes water retention and increased appetite. And while prednisone is a catabolic hormone, meaning it causes the breakdown of fat and protein, these effects are more than offset by its appetite stimulating properties. To make matters worse, excess calories consumed in the setting of elevated corticosteroid levels tend to be preferentially deposited around the middle.

Alternatives: Doctors should prescribe prednisone when there is no option for a less potent drug. If you must take prednisone or any steroid, it is very important to be aware of its ability to increase appetite and watch your calorie intake very carefully.

5) Seizure Drugs & Mood Stabilizers

These drugs include Depakote, Risperdal and Olanzapine. The weight gain associated with these medications is often rapid and significant, with research showing as much as a 37 pound weight gain during the course of treatment.4 Scientists believe the drugs’ action on the histamine receptor in the brain is responsible for the effect.5

Alternatives: Discuss this with your doctor. People taking these medications need to be aware of the potential for weight gain and work with a qualified professional to mitigate this side effect as much as possible. Since weight gain can be rapid, it is a good idea to start as soon as treatment commences.

6) Insulin & Other Diabetes Drugs

Since weight loss is a primary goal of treating type 2 diabetes, it seems illegal that some of the most commonly used drugs to lower blood sugar can cause significant weight gain. When a patient is diagnosed with diabetes, there is often a frantic rush to get the blood sugar down using any means necessary. By giving insulin or insulin releasing agents, sugar is removed from the blood stream and often stored as fat. The result is a lower blood sugar but often 10 or more extra pounds of fat, which can then increase medication requirements and cause more fat storage.6 This vicious cycle continues and makes it essentially impossible for many patients to ever get off medication. Additionally, aggressive blood sugar lowering effects can often cause hypoglycemia, or too low blood sugar, when must be remedied by eating sugar (Often diabetics will need to eat candy or drink juice to get their blood sugar up.) which causes more fat gain from the extra calories.

Alternatives: There is no easy answer here. Short-term blood sugar lowering must be viewed in a long-term context. This is certainly a controversial area where mainstream medicine often differs in opinion from complimentary or alternative medicine. If you find yourself familiar with the scenario laid out above, educate yourself and find a qualified professional whom you trust to work with.

This is not to propose that you should not take a medication if your doctor says it is necessary. But if you are taking a medication that can contribute to weight gain, it helps to know ahead of time and create a plan to attempt to negate some of the weight gain side effect.


  • lami says:

    how do I gain Weight in two weeks

    • Kristin Rooke, CPT says:


      If you're focused on gaining weight, I think it's important to determine whether you want to increase your muscle mass, or just increase your weight overall. You can gain weight by eating more calories than you burn. Increase your consumption of protein, fats, and carbohydrates. Fats are incredibly calorie-dense (1 gram of fat contains 9 calories), which makes it a great macronutrient to eat more of when your goal is weight gain.

      But, if you want to gain lean muscle and limit the amount of fat you put on, then you'll want to eat protein with every meal, eat a slight excess of calories, and follow a workout program designed to increase muscle mass.

      Hope that helps! If you have more questions, feel free to ask.

      -Kristin, BuiltLean Coach & Managing Editor

  • Zethu says:

    Please help i want to gain weight on legs and buttocks ,what pills should i take

    • Kristin Rooke, CPT says:


      If you want to increase the size of your glutes and legs, I would recommend focusing on a muscle building program as opposed to supplements. Supplements (like gainers) are usually VERY calorie dense and cause you to gain more fat than necessary. Instead, add squats, lunges, deadlifts, and step ups to your workout program, while eating ample protein at each meal and a slight excess of calories overall. That's how you can add lean muscle to your lower body and frame.

      I hope that helps! If you have more questions, feel free to reach out at support@builtlean.com.

      -Kristin, BuiltLean Coach & Managing Editor

  • cecilia says:

    Please help! I am very lean and I need a drug that can make me get fat in 3 days, or 1 week. I need it badly because people are complaining that am too lean.

    • Kristin Rooke, CPT says:

      Hi Cecilia,

      We don't promote or recommend any specific drugs or supplements. Instead, we believe in a whole foods approach to nutrition, and a well-rounded approach to exercise. If you're too lean, I highly recommend speaking with your primary care doctor or a registered dietician. A dietician will be able to assess your current eating habits, and help you design a balanced, nutrient-rich nutrition plan to help you gain weight in a safe and healthy way.

      I hope that helps!

      -Kristin, BuiltLean Coach & Managing Editor

  • Bruno says:

    Is there any drug I can take to make me grow fat even without having much time for food?

    • Kristin says:

      Hi Bruno, first and foremost, since we're not medical professionals, we're not allowed to prescribe any drugs or supplements. Additionally, we don't recommend taking drugs or supplements to change your weight. Reason being, drugs often come with negative side effects (and could have some negative health consequences). If you want to gain weight despite having little time for food, I would recommend eating foods that are higher in healthy fats - for example, nuts & nut butters, avocados, olive oil, coconut oil, coconut milk, cheese, full-fat yogurt, and fatty fish. You could make a protein- and fat-rich protein shake for breakfast using a protein powder, coconut milk, a spoon of nut butter, and a banana. You could add avocado and olive oil to your lunch. And you could put cheese and coconut oil on your dinner. Gaining weight requires you to take in more calories than you burn. Since fats contain 9 calories per gram (whereas protein and carbs contain 4 calories per gram), eating more fat is a great way to easily increase your calorie intake in a healthy way. Hope that helps!
      -Kristin, BuiltLean Coach & Managing Editor

  • dagmo says:

    you are the best Kristin..I love yah

  • Dehooya Gusita says:

    My wife wants to gain weight she was sixty kgs but now is forty seven kgs am in uganda and still i can make marketing in uganda as adistributor.

  • Jitu says:

    Please help me...
    I want to gain weight as soon as possible without any side effect

    • Marc Perry, CSCS, CPT says:

      Eating more food is probably the healthiest option in addition to resistance training