Medicines and weight gain

Also called medicine-related weight gain

Key points about medicines and weight gain

  • Some medicines can cause weight gain as a side effect in some people. The amount of weight gained may vary depending on the individual and type of medication.
  • Weight gain may not be problematic for everyone. If you are underweight or average weight, gaining a few kilos might not be a big deal. But if you are already overweight, gaining more weight can be a concern.
  • Medicines can cause weight gain in a number of ways.
  • Sometimes there might be a different medicine that you can take that has less effect on your weight.
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Medicines can cause weight gain in a number of ways, such as by:

  • stimulating your appetite, making you feel hungry and eat larger portions and more often
  • affecting the way your body stores fat
  • slowing your metabolism, which causes your body to burn calories at a slower rate
  • making you retain fluid
  • affecting your ability to exercise, eg, by causing shortness of breath or making you feel too tired to exercise.

For some medicines, it isn't exactly clear what triggers the weight gain.

The following is a list of medicines that are known to cause weight gain in some people. It is important to note that not all people gain weight with these medicines. If you are taking a medicine and are worried about weight gain do not stop taking your medicine suddenly. Instead discuss this with your doctor or pharmacist.

Sometimes there might be a different medicine that you can take that has less effect on your weight. Also, the risks of stopping or changing medicines should be balanced against the risks of gaining weight and related health effects.

Medicines that are known to cause weight gain in some people
  • Medicines for diabetes such as insulin and sulfonylureas.
  • Antipsychotics such as haloperidol, clozapine, lithium, olanzapine.
  • Antidepressants such as amitriptyline, paroxetine, sertraline.
  • Medicines for epilepsy such as sodium valproate, carbamazepine.
  • Beta-blockers such as metoprolol, atenolol and propranolol.
  • Steroid medicines such as prednisone, dexamethasone.
  • Oral contraceptives (birth control pills).
Note: Not all medicines of these types cause weight gain, eg, metformin (a drug used for diabetes) and topiramate (a drug used for seizures and migraines) might make you lose weight instead of gain it.

Since not all weight gain is caused by medicines, working out whether your weight gain is caused by your medicine is not always easy. Your doctor will look at your medicine list to see whether you are taking any that can cause weight gain. If you started gaining weight when you began one of these medicines, then it could be partly to blame.

To work out whether a medicine is responsible for your weight gain, your doctor will note your change in weight compared with records from your past medical appointments. They may ask you about changes in your eating or exercise habits. They may also do a physical exam to make sure your weight gain isn’t caused by something else.

Discuss this with your doctor or pharmacist. If you are worried about putting on weight, don't stop taking your medicine suddenly. Rather, discuss this with your doctor or pharmacist. Sometimes a more suitable medicine can be found. Some medicines need to be stopped gradually, as stopping suddenly can make you feel very unwell. They may discuss various weight loss options that best suit your needs. Read more about options for weight loss

Ask for a referral to a dietitian or a nutritionist. They will be able to offer you guidance on healthy eating plans and practical advice on foods choices.

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Credits: Sandra Ponen, Pharmacist, Healthify He Puna Waiora. Healthify is brought to you by Health Navigator Charitable Trust.

Reviewed by: Angela Lambie, Pharmacist, Auckland

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