How to Take Levothyroxine to Lose Weight?

Synthroid to Lose Weight

Sometimes losing a single pound of weight is so difficult that people try to seek alternative unapproved medications for weight loss. Levothyroxine is one of the drugs people are still using to lose weight. How to take Levothyroxine to lose weight if you have hypothyroidism?

Apart from some important information about Synthroid, I’ll try to answer the following questions in this article:

  • Does Synthroid (Levothyroxine) help you lose weight?

  • Should people without hypothyroidism take levothyroxine to lose weight?

  • How can you lose weight with thyroid medications?

  • How to Take Levothyroxine to Lose Weight?

  • What are the important side effects of levothyroxine?

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What is Synthroid?

Synthroid is the brand name of Levothyroxine or L-thyroxine. It is different from triiodothyronine or T3. T3 or triiodothyronine is the active form of thyroxine and has a short duration of action.

Because T3 is the most active form of thyroxine, it is highly associated with serious cardiac side effects. It is only advised in patients with severe hypothyroidism who are critically ill.

Synthroid on the other hand is T4 or levothyroxine. Levothyroxine is a man-made form of thyroxine while thyroxine is endogenously synthesized in the body. However, they may be used synonymously.

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Synthroid or Levothyroxine Use:

Synthroid or levothyroxine is used to treat hypothyroidism. Hypothyroidism is an endocrine disorder caused by insufficient production of thyroxine by the thyroid gland. If the problem is in your thyroid gland, the condition is called primary hypothyroidism.

It is also indicated in the treatment of secondary hypothyroidism. Secondary hypothyroidism is also called central hypothyroidism. In most cases of secondary hypothyroidism, the pituitary gland is not working properly.

The pituitary gland in normal people produces TSH (thyroid-stimulating hormone) that stimulates and activates the production of thyroxine by your thyroid gland. If the stimulus is not properly generated because of a problem in the pituitary gland, thyroxine will not be produced.

Sometimes Synthroid (levothyroxine) is prescribed to people with thyroid cancer despite normal levels of the body’s own thyroxine. In such cases, a small amount of levothyroxine is added to suppress the growth of the thyroid nodule and prevent the recurrence of the disease.

Levothyroxine has an onset of action of about 3 to 5 days when given orally. It is better absorbed in the fasting state. About 80% of levothyroxine gets absorbed when it is taken in the fasting state. In the fed or post-meal state, only 64% of the drug gets absorbed.

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Does Levothyroxine (Synthroid) help you Lose Weight?

The answer is YES. Synthroid (Levothyroxine) increases your metabolic rate. With Synthroid use, your body starts working faster. Almost all of your body’s functions are accelerated with levothyroxine use.

If you have hypothyroidism, a condition when your body’s normal thyroid gland is not producing sufficient thyroxine, your body starts retaining salt and water. In addition to salt and water retention, your metabolic rate decreases.

This leads to the slow processing of the foods you take. Hence, even small amounts of the food you take are stored in your body as fats.

Once you start taking Synthroid (Levothyroxine), your body starts getting rid of the extra salt and water. You may immediately notice some weight loss. This is then followed by the excess of fat loss from your body that accumulated as a result of your hypothyroid state.

It has been estimated that a person with hypothyroidism loses about 10% of the body weight during the first six months to one year of treatment with Synthroid (levothyroxine).

During the first 24 months of treatment, 52% of hypothyroid patients lost weight with levothyroxine treatment initiation. The average weight loss observed with Synthroid was 8.4 lbs +/- 9.7 lbs [Ref].

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Should people without hypothyroidism take Levothyroxine (Synthroid) to lose weight?

Levothyroxine can be used by people without hypothyroidism only under certain conditions:

People treated for thyroid cancer after surgery to suppress the TSH (thyroid-stimulating hormone):

  • Suppressive doses of thyroxine are given to prevent the recurrence of thyroid cancer and the growth of the thyroid nodule. The dose of thyroxine is adjusted to maintain the TSH at the lower limits of the reference ranges and not lower than 0.1 mIU/L

People with subclinical hypothyroidism: 

  • Subclinical hypothyroidism is a condition when the thyroxine or free T4 levels in the body are within the normal range while the TSH is above the normal range.
  • Patients with subclinical hypothyroidism only require treatment if they meet the following criteria:
    • The TSH is above 10 mIU/L
    • The patient has an enlarged thyroid gland
    • Pregnant females
    • Symptomatic individuals such as those who are very obese, have obstructive sleep apnea, diabetes, hypertension, and depression, and
    • Patients with a positive anti-TPO (anti-thyroid peroxidase antibody) test. A positive anti-TPO antibody suggests Hashimoto’s thyroiditis. Such patients eventually develop frank hypothyroidism.

In the absence of the above two conditions, it is not recommended to take thyroxine for weight loss. The use of Levothyroxine in patients without hypothyroidism can result in serious heart-related side effects.

A US Boxed Warning has been issued if people use it for weight loss without hypothyroidism because of serious cardiac events including Myocardial infarction (heart attack), Angina, and Arrhythmias.

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How can You Lose Weight with Levothyroxine?

Hypothyroidism causes fluid and water retention. It also impairs the metabolism of fats, proteins, and carbohydrates. Thus, Levothyroxine replacement reverses these metabolic derangements.

It has been associated with about 10% weight loss. during the first 06 to 12 months of treatment initiation.

In one study, the extra weight loss was estimated to be 26% fats and 74% fat-free tissue including muscles. Other studies in hypothyroid patients have also observed impaired fat metabolism that is corrected when levothyroxine is administered.

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How to take Levothyroxine to Lose Weight?

Hypothyroidism and Obesity are interrelated. Hypothyroidism causes obesity, on the other hand, obese people have been found to have impaired or insufficient thyroid production or thyroid activity.

Levothyroxine is usually administered before meals, preferably 30 minutes before breakfast. Meals impair the absorption of Synthroid. In the fed state, only 64% of the drug gets absorbed while in the fasting state, 80% of the drug gets absorbed.

Along with Levothyroxine, it is important to follow a low-calorie diet and indulge in activities that help you lose calories. Some natural ways of losing weight are regular walking, reducing the portion of your meals, and eating meals that have few calories.

For the treatment of hypothyroidism, Levothyroxine is usually continued lifelong. You can not discontinue it even if your blood test is normal. If your TSH is lower than the normal range, you have to reduce your dose and vice versa.

If you have central hypothyroidism, you don’t need to check your TSH levels. Free T4 is used to monitor the response to treatment.

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Why You Should Not Use Levothyroxine (Synthroid) for Weight Loss if You do not Have Hypothyroidism?

Synthroid and other thyroid medications increase your body’s metabolic rates. This also includes your heart rate, respiratory rate, and oxygen demand.

The use of Synthroid in patients without hypothyroidism can result in myocardial infarction, angina, and cardiac arrhythmias. It can also cause muscle wasting and protein loss in your body.

If you have a condition called adrenal insufficiency, levothyroxine can unmask it and you can go into an acute adrenal crisis. Adrenal insufficiency is a condition when your body is not producing enough cortisol. This condition can occur in patients with hypothyroidism as in polyglandular syndromes.

Acute adrenal crisis is an acute emergency that manifests as hypotension, dehydration, nausea, vomiting, abdominal pain, low sodium, and high potassium in the blood. It is rapidly corrected with intravenous fluid administration and cortisol administration.

Levothyroxine also weakens your bones. It can cause osteoporosis, especially in elderly patients. It may also impair your blood glucose levels especially if you have diabetes [Ref].

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In conclusion:

Synthroid or Levothyroxine is a life-saving drug. However, it should not be used to treat obesity in the euthyroid state (normal thyroid function). It can cause serious cardiac diseases like myocardial infarction, angina, arrhythmias, and heart failure.

In hypothyroid patients, it can be taken before meals. It can cause a weight loss of about 10% of your body in the first few months of treatment initiation.

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Written by Dr. Ahmed

I am Dr. Ahmed (MBBS; FCPS Medicine), an Internist and a practicing physician. I am in the medical field for over fifteen years working in one of the busiest hospitals and writing medical posts for over 5 years.

I love my family, my profession, my blog, nature, hiking, and simple life. Read more about me, my family, and my qualifications

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