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Does levothyroxine cause weight gain?

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Weight gain side effectHow to manage weight gainOther side effectsWeight loss drugs and levothyroxineStopping levothyroxineSummary
Levothyroxine does not directly cause weight gain, though it may increase your appetite. Still, it may be more likely to cause weight loss as it restores your thyroid function and metabolism.
Medically reviewed by Ami Patel PharmD, BCPS
Updated on November 27, 2023

The medication levothyroxine helps regulate thyroid hormone levels in people who live without a thyroid gland, have certain cancers, or experience an underactive thyroid (also known as hypothyroidism).

Among many other roles, thyroid hormones help regulate your metabolism, including energy use and growth.

Low levels of thyroid hormones may slow down the process in which your body gets energy from food, causing various symptoms, including weight gain.

The American Thyroid Association (ATA) explains that hypothyroidism may present as:

  • persistent tiredness
  • dry skin and thinning hair
  • constipation
  • forgetfulness
  • depression
  • weight changes
  • poor tolerance to cold temperatures

In the United States, you can purchase different brand versions of levothyroxine, including: 

Need a refill for levothyroxine (Synthroid)? You may be able to get an online prescription through Optum Perks in as little as 15 minutes with no video or appointment needed. Learn more here.

Is weight gain a side effect of levothyroxine?

Woman taking levothyroxine for hypothyroidism walking around the city
FG Trade/Getty Images

Weight gain is not a commonly reported side effect of levothyroxine. The medication restores levels of thyroid hormone. When that happens, essential body functions, including metabolism, return to working as they should. This is why levothyroxine isn’t likely to cause weight gain. In fact, it’s more likely to cause weight loss within 6 weeks. 

Package labels for generic levothyroxine and the brand Euthyrox mention weight loss as a possible side effect of taking the medication.

The ATA also explains that weight loss is possible after starting hypothyroidism treatment but clarifies that it’s likely to be less than 10% of your body weight. 

Individual responses to levothyroxine may vary. For instance, some people may experience changes in their appetite, which may lead to weight gain or loss.

How to manage weight gain from levothyroxine

If you’re concerned about weight changes while taking levothyroxine, these strategies may help:

  • Eating habits: Focus on a balanced diet with plenty of fruits, vegetables, lean proteins, and whole grains. Avoid eating foods high in calories but low in nutrients, which may contribute to unintended weight gain. You can learn more in the Dietary Guidelines for Americans
  • Regular physical activity: Movement helps you stay healthy and manage your weight. The Physical Activity Guidelines for Americans recommends that adults get at least:
    • 150 minutes of moderate-intensity or 75 minutes of vigorous-intensity cardio exercise per week
    • two strength training sessions per week
  • Thyroid monitoring: Adjustments in your levothyroxine dose may be necessary to maintain needed thyroid levels, which can help you manage your weight. The ATA recommends that you see a healthcare professional 6–10 weeks after starting levothyroxine treatment or changing the dose. If you’re active but still gain weight, you may need a higher dose of levothyroxine.
  • Consult a healthcare professional: If you experience significant weight changes or unusual or severe symptoms after starting levothyroxine, a healthcare professional can offer personalized guidance. They can also support you with information on sustainable diet and exercise changes that suit your lifestyle and health. 

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Side effects of levothyroxine

While weight gain is not a direct side effect of levothyroxine, the medication may have other potential side effects. 

Common side effects listed on the medication label are:

  • increased appetite
  • weight loss
  • excessive sweating
  • nervousness, irritability, or anxiety
  • muscle tremors or weakness
  • increased pulse or blood pressure
  • diarrhea 
  • menstrual changes (if you menstruate) 
  • hair loss
  • flushing or a rash
  • changes to bone density
  • nausea or vomiting

Side effects may occur if your dose is too high or if you’re sensitive to the medication. Working closely with a healthcare professional to find the right dosage for balancing your thyroid levels and minimizing side effects is important.

Can you take weight loss drugs if you take levothyroxine?

This depends on your needs, medication, and healthcare professional’s recommendations. Supplements and medications can affect the absorption and safety of levothyroxine and could also worsen hypothyroidism symptoms. This includes some weight loss drugs. 

For instance, the levothyroxine label notes that the weight loss medication orlistat (Alli, Xenical) can lower levothyroxine absorption. 

Before taking levothyroxine, let the prescribing doctor know about any other medications you take or plan on taking. They can advise whether it’s safe and suitable to take weight loss drugs while on treatment or suggest alternatives.

Can you stop taking levothyroxine?

If a healthcare professional prescribes levothyroxine for an underactive thyroid, you typically need to take it for life.

Stopping the medication suddenly may adversely affect your thyroid function and overall health. But it’s possible that your healthcare professional adjusts your dose depending on your needs. This may mean increasing or decreasing the amount of levothyroxine you take daily.

Some people may be able to stop levothyroxine treatment after some time. But a healthcare professional must establish a tapering plan to do so safely. 

Always consult a healthcare professional before changing your thyroid medication regimen.

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Levothyroxine is not a direct cause of weight gain, though some people may experience increased appetite as a side effect. More likely, levothyroxine may contribute to weight loss as it restores thyroid levels, metabolism, and energy use. Still, individual responses to levothyroxine may vary.

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