Levothyroxine for weight loss: myths and risks

What is levothyroxine?

Levaxin is a medicine used for thyroid disorders and replaces missing or low production of thyroid hormones. Levothyroxine is a synthetic hormone that works in the same way as the body’s natural hormone. Thyroid hormones regulate basal metabolic rate and therefore affect energy expenditure, temperature regulation and several organ systems.

Correct use of levothyroxine is important to ensure both effectiveness and safety. Levothyroxine is a prescription-only medicine and should only be used as prescribed by a doctor.

Can you lose weight with levothyroxine?

With untreated hypothyroidism: some weight loss may occur – but it is usually limited

In people with untreated hypothyroidism, low thyroid hormone levels can contribute to a reduced metabolic rate and increased fluid retention. This can lead to weight gain.

Other symptoms associated with hypothyroidism can include fatigue and low energy, which may reduce physical activity.

When treated with levothyroxine, metabolism is normalised and fluid-related weight may decrease. This happens because metabolic function is restored, not because the medicine itself has a direct fat-burning effect. With improved energy levels, it can also become easier to live a more active life, both through everyday movement and structured exercise.

Overall, levothyroxine can help the body return to normal hormonal balance in hypothyroidism, but it is not a weight-loss treatment and should not be used for that purpose.

With normal thyroid function: no – and it can be dangerous

According to the official product information for levothyroxine:

• Levothyroxine is not indicated for the treatment of overweight or for weight loss
• Taking levothyroxine when thyroid hormone levels are normal does not lead to weight loss
• Doses above physiological needs can cause serious side effects, including effects on the heart, reduced bone density and other potentially life-threatening complications

The risk increases further if levothyroxine is taken alongside other medicines intended for weight loss, or if the dose is changed without medical follow-up.

In summary:
Taking levothyroxine to lose weight when thyroid function is normal is both ineffective and associated with medical risks. Levothyroxine treatment should always be used only for a clear medical indication and under regular monitoring by a doctor.

Risks with incorrect use

Using levothyroxine incorrectly or at too high a dose can increase the risk of several negative effects:

• palpitations and heart rhythm disturbances
• reduced bone density and a higher risk of osteoporosis
• anxiety, sweating and restlessness

Both European and American guidelines highlight these risks and clearly advise against attempting to use levothyroxine as a “shortcut” to weight loss.

If you have questions about dosing or side effects, you should always contact a doctor.

What works for weight loss?

Research shows that approaches associated with sustainable weight loss for people living with overweight or obesity include:

• changes to eating habits
• optimising everyday movement and exercise
• sufficient, good-quality sleep and stress management
• behavioural support and follow-up
• medical weight-loss treatment when needed and appropriate

Healthy lifestyle changes: diet and exercise for weight loss

If weight loss is the goal, it’s important to understand how diet and physical activity affect both weight and health. A balanced diet that is nutrient-rich and appropriately energy-controlled is crucial for long-term, healthy results. Many patients find that good eating habits, together with medical treatment, help them feel better and have more energy in everyday life.

There are many ways to improve diet during weight loss. Increasing vegetables, fruit and wholegrains often helps, providing lots of nutrients with fewer calories. Drinking enough water, avoiding added sugar and reducing saturated fat are also useful strategies. It’s important to remember that everyone’s needs are different, and individual support from a dietitian or doctor may be needed to find the right balance.

The importance of physical activity for weight loss

Physical activity is a central part of weight-loss treatment.

Recommended types of activity include:

• Everyday movement: take the stairs, walk or cycle
• Cardio activity: for example brisk walking, swimming or cycling
• Strength training: 2–3 times per week to preserve muscle mass and support metabolism

Exercise should be adapted to the individual’s circumstances, health status and goals.

Increased risk – speak to a doctor

Levothyroxine is used to treat underactive thyroid function, and it’s important to take it as prescribed. If you have questions about how the medicine affects weight, or how treatment can best be combined with other medicines, conditions, diet and physical activity, you should always contact a doctor to avoid health risks. A doctor can advise on how to reduce side effects and achieve the best possible treatment outcome.

Medicines for weight loss

There are approved medicines with well-studied, evidence-based effects that can be used as support in the medical treatment of overweight and obesity. Before starting any new medicine-based treatments, it’s important to check with a doctor that they are safe and compatible with any other treatments and medical conditions. This helps reduce the risk of unwanted effects and supports better long-term results.

Weight loss is often a journey that requires patience, the right support and a whole-person approach to health. By combining a nutritious diet, physical activity and appropriate treatment, the chances of reaching goals and improving long-term health increase. The most important thing is not only to reduce weight, but to build habits that give more energy, better wellbeing and a lower risk of future disease.

Summary

Levothyroxine is a medical treatment for hypothyroidism. It is not a method for weight loss. In people with an underactive thyroid, correctly adjusted treatment can help restore hormonal balance and, in some cases, reduce weight that is related to the hormone deficiency. For people with normal thyroid function, however, there is no evidence that levothyroxine leads to sustainable, healthy weight loss, and using it for this purpose can carry significant health risks.

Sustainable weight loss is instead built on a combination of structured lifestyle habits, support from healthcare professionals and, when appropriate, medical treatment designed for weight management. At Yazen, the focus is on safe, evidence-based and personalised support that avoids guilt and shame, and provides tools that truly work in the long term.

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