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Can Tirosint cause weight gain or loss?

Medically reviewed by Carmen Fookes, BPharm. Last updated on Sep 16, 2021.

Official answer


Although weight loss can be a side effect of Tirosint in people taking it for low thyroid levels (hypothyroidism), you should not take Tirosint for the sole purpose of losing weight. Using Tirosint to reduce weight in people with normal thyroid levels is dangerous, not safe, and can be life-threatening. Strokes, seizures, shock, coma, and death have been reported in people who have taken higher than recommended dosages of thyroid hormone preparations for weight loss. Some symptoms of Tirosint toxicity (overdose), such as confusion, disorientation, sleep disturbances, or heart changes may not appear until several days after ingestion. Tirosint should not be used as a treatment for weight loss or obesity.

It is not uncommon for people with low thyroid levels to lose up to 10% of their body weight when starting thyroid medications, such as Tirosint. This weight is mainly water weight, since being hypothyroid makes you retain water and weight gain is one of the symptoms of hypothyroidism. Taking thyroid replacement therapy may reverse that weight gain. You may return to the normal body weight you would have been without the fluid retention caused by hypothyroidism. Once your thyroid levels are normal again, this medication should not affect your weight.

Tirosint has a narrow therapeutic index – this means there is a fine line between taking too much or having too little. Over or under treatment can be detrimental to cardiovascular function, bone metabolism, reproductive health, emotional state, gastrointestinal function, glucose and lipid metabolism, and a young person’s growth and development.

Tirosint is a brand of levothyroxine (also known as T4) manufactured by IBSA Pharma Inc., a multinational pharmaceutical company with its headquarters in Lugano, Switzerland. Levothyroxine is a man-made form of thyroxine, a hormone that is produced naturally in the body by the thyroid gland. Tirosint replaces missing thyroxine in people whose thyroid glands do not produce enough thyroxine naturally.

Thyroid hormones (such as levothyroxine) play a vital role in our normal growth and development, and the maturation of our brain, spinal cord, nerves, and bone. Thyroid hormones help cells function and are also involved in their breakdown. They also help regulate our moods, reproductive function, metabolism, and gastrointestinal function. Tirosint is generally taken life-long when used to treat hypothyroidism (low thyroid levels) unless the cause is transient.


Tirosint (levothyroxine) Updated 09/2020[CF1] IBSA Pharma Inc.

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