L-Thyroxine, or levothyroxine as it is commonly known, is a non-proteinogenic amino acid that functions as a hormone in the body. Like iodine, it is an important element of metabolic processes in the thyroid gland.

As opposed to most other amino acids, levothyroxine is strictly a medication.

Applications of Levothyroxine

Levothyroxine is prescribed in cases of an underactive thyroid (hypothyroidism). Levothyroxine may also be used as a companion therapy in cases of overactive thyroid (hyperthyroidism), provided this condition is successfully treated with thyrostatic drugs.

The dosage for newborns and young children is approx. 10 to 15 µg (micrograms) per kilogram of body weight. Untimely treatment of hypothyroidism in newborns may lead to impairments in mental and physical development.

For long-term therapy, daily dosages are generally between 12.5µg and 200µg.

Levothyroxine can also be used as a diagnostic tool to detect malfunctions of the thyroid gland.

If you are taking levothyroxine in tablet form, you should ingest it on an empty stomach before breakfast.

Side Effects

Taking levothyroxine may boost energy metabolism. It should be noted, however, that levothyroxine is never to be considered a “weight loss drug.”

An increased risk of osteoporosis has been observed in post-menopausal women who are on levothyroxine therapy. Overdosing can lead to serious complications such as insulin resistance, and may even lead to death.

Drug Interactions

Taking calcium or iron with levothyroxine may significantly reduce the bioavailability of the medication 1. Therefore, do not take iron or calcium supplements while on levothyroxine therapy, or be sure to to discuss this with your physician before taking these supplements.

Prevalence of Application

Levothyroxine is one of the most commonly prescribed drugs. In total, physicians in Germany alone prescribe approx. 1.2 billion daily doses per year.

Important Notice: Information presented here serves as general information only and does not ever replace the advice of a physician or pharmacist. Levothyroxine is a prescription medication and any use thereof should be done under the supervision of a licensed physician.


  1. Mersebach H, Rasmussen AK, Kirkegaard L, Feldt-Rasmussen U. Intestinal adsorption of levothyroxine by antacids and laxatives: case stories and in vitro experiments. Basic and Clinical Pharmacology and Toxicology. 1999. 84(3):107-109
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