Cow's Milk Interferes with Absorption of Thyroid Supplement Levothyroxine

Taking the common oral thyroid hormone medication levothyroxine with a glass of cow’s milk significantly decreases the body’s ability to absorb the drug, a preliminary study finds. Results will be presented Sunday at ENDO 2017, the Endocrine Society’s 99th annual meeting in Orlando, Fla. “These findings support previous research showing that calcium supplements can interfere with levothyroxine absorption,” said principal investigator Deborah Chon, M.D., an endocrinology fellow at the UCLA David Geffen School of Medicine and the VA (Veterans Affairs) Greater Los Angeles Healthcare System, Los Angeles, Calif. “Decreased absorption means that patients may not get the full dose of thyroid hormone that they are prescribed.”Although it makes sense that milk, which contains calcium, might interfere with levothyroxine absorption, no study has proved that it does until now, according to Chon.

Levothyroxine is prescribed for patients with an underactive thyroid, called hypothyroidism, to replace the natural thyroid hormone thyroxine (T4) that is too low, or for patients with thyroid cancer, to suppress their thyroid stimulating hormone levels. In 2014, levothyroxine was the most commonly prescribed medication in the U.S., a survey from the IMS Institute for Healthcare Informatics (now QuintilesIMS) found.

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THYROIDSandra Ishkanes