Does levothyroxine cause weight gain?

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.

An underactive thyroid may slow down the process by which your body gets energy from food. In turn, this can cause various symptoms, including weight gain.

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

• Synthroid
• Euthyrox
• Unithroid
• Ermeza
• Levo-T
• Levoxyl
• Tirosint

Need a refill for levothyroxine (Synthroid)? You may be able to get an online prescription through Optum Perks in as little as 15 minutes. Learn more here.

Does levothyroxine cause weight gain or weight loss?

Weight gain is not a commonly reported side effect of levothyroxine. In fact, it’s more likely to start causing weight loss within the first 6 weeks.

This is because weight gain is a common symptom of hypothyroidism, which levothyroxine is prescribed to treat. Levothyroxine restores levels of thyroid hormone. When that happens, essential body functions — including metabolism — return to working as they should. If you gain weight due to an underactive thyroid, taking levothyroxine may help you lose it.

It’s important to note that 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:

• Thyroid monitoring: Adjustments in your levothyroxine dose may be necessary to maintain regular thyroid levels, which can help you manage your weight. Your doctor will monitor your thyroid condition throughout treatment, especially after adjusting your levothyroxine dose. If you’re active but still gain weight, you may need a higher dose of levothyroxine.
• 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.
• Regular physical activity: Movement helps you stay healthy and manage your weight. The Physical Activity Guidelines for Americans recommend 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
• 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 possible side effects. 

Common side effects listed in the prescribing information 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 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 to take weight loss drugs while on treatment or suggest alternatives.

Can you stop taking levothyroxine?

If a healthcare professional prescribes levothyroxine for your underactive thyroid, you’ll likely take it long term.

Stopping the medication suddenly may adversely affect your thyroid function and overall health. However, your healthcare professional may adjust 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. However, 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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Summary

Levothyroxine is not a direct cause of weight gain. More likely, levothyroxine may contribute to weight loss as it restores thyroid levels, metabolism, and energy use. Still, individual responses to levothyroxine may vary. If you experience weight gain with levothyroxine, it may be a sign that your dosage is too low.