Levothyroxine & weight loss

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Doctors use the synthetic thyroid hormone levothyroxine to treat hypothyroidism, which occurs when the thyroid does not release enough hormones to regulate metabolism, and users have taken it to manage obesity or lose weight while bodybuilding.

Patients with certain pre-existing conditions should not take levothyroxine as its use can lead to a number of detrimental side effects.


Levothyroxine, also referred to as L-thyroxine or T4, is a synthetic version of the naturally occurring thyroid hormone thyroxine. Drugs.com reports that doctors use levothyroxine to reduce the size of goitre, which are swellings in the thyroid, and to treat patients who suffer from hypothyroidism.

According to the Mayo Clinic, the most common cause of hypothyroidism is an autoimmune disorder, Hashimoto thyroiditis, in which the body's immune system attacks the thyroid and impairs its ability to produce hormones. Hypothyroidism may also result from atrophy, injury or damage to the pituitary gland, hypothalamus, or thyroid caused by surgery, cancer, radiation or the effects of other drugs. The Mayo Clinic reports that congenital hypothyroidism--a baby has either no thyroid gland or one that does not function properly--occurs once in every 3,000 births.


In healthy patients, thyroxine stimulates and regulates the metabolism of fats, carbohydrates and vitamins. It also affects protein synthesis, and it interacts with human growth hormone to regulate bone growth.

Thyroxine controls the body's rate of metabolism, and it increases the rate of metabolism for almost every cell in the human body. Because of this, Mesomorphosis.com reports, individuals looking to lose weight have taken levothyroxine in greater than prescription doses to burn off more calories, to increase protein synthesis to build more muscle, and to shed fat.

Weight Loss Dosages

The bodybuilding website mesomorphosis.com reports that many bodybuilders use levothyroxine during their "cutting phase," in which they seek to burn off excess body fat. Bodybuilders also combine levothyroxine with human growth hormone during pre-contest preparation to preserve muscle while burning off calories and fat. Mesomorphosis.com reports that bodybuilders have used levothyroxine in daily dosages of 300 micrograms.


Medicinenet.com reports that levothyroxine is not approved for use in treating obesity or for managing weight or promoting weight loss. The site further cautions users against using synthetic thyroxine for any of those purposes, and it warns against combining levothyroxine with any diet or other weight loss medication or supplement. Users who fail to heed these warnings may suffer toxic effects or overdose as a result.

Levothyroxine is not recommended for patients who have recently suffered a heart attack, or those with coronary artery disease, clotting problems, osteoporosis or impaired pituitary or adrenal function.

Additionally, drugs.com reports that levothyroxine will affect the activity of anticoagulants, blood thinners, cholesterol medications, amphetamines, asthma medicine and insulin. Patients taking any of these drugs are advised to consult a physician before using levothyroxine.


Patients taking levothyroxine for hypothyroidism receive dosages partly adjusted by age and body weight. For example, an adult less than 50 weighing 68kg. might take 100 to 125 mcg of Synthroid daily.

According to drugs.com, users seeking to lose weight or manage obesity with levothyroxine can overdose and may experience life-threatening symptoms that include coma, heart failure, low blood sugar and fever.


Drugs.com reports that individuals taking levothyroxine have reported allergic reactions including laboured breathing, swelling of the face and mouth, itching, hives and chest pain. Patients also have reported weight loss, weight gain, oedema (swelling of legs and ankles), clumsiness, lethargy, lethargy, coldness, menstrual dysfunction, insomnia, moodiness, weakness, irregular heartbeat, insomnia, headache and changes in appetite.