Informing & Supporting Thyroid Patients Since 1985
Informing & Supporting Thyroid Patients Since 1985
Thyroid Research 
Thyroid Research Archive Thyroid Horme Therapy
(November 2003)
The background of the study. Several drugs and high doses of iron and calcium decrease the intestinal absorption of thyroxine (T4) in patients with hypothyroidism. This case report describes a patient in whom raloxifene, a selective estrogen-receptor modulator, caused a decrease in the absorption of T4.
Case report. A 79-year-old woman with hypothyroidism treated with 0.15 mg of T4 daily was well and had normal serum thyrotropin (TSH) concentrations for several years. She was found to have low bone density, and was treated with 60 mg of raloxifene daily, which she took with the T4 early in the morning. She began to have symptoms of hypothyroidism, and a month later her serum TSH concentration was high (14.5 mU/L). The dose of T4 was increased to 0.2 mg daily, but she continued to have symptoms; four months later her serum TSH concentration was 21.4 mU/L. The dose of T4 was raised to 0.3 mg daily; two months later her serum TSH concentration was 9.4 mU/L. She had no symptoms of malabsorption of food.
She was advised to take T4 and raloxifene at different times; two months later her serum TSH concentration was 0.6 mU/L. She then took the T4 and raloxifene at the same time, and a month later her serum TSH concentration was 13.0 mU/L; it fell to 2.2 mU/L when she again took the T4 and raloxifene separately.
On two occasions she was given 1 mg of T4, once without and once with 60 mg of raloxifene, and serum T4 was measured at frequent intervals for six hours. There was a smaller rise in serum T4 concentration when she took the two medications together.
The conclusions of the study. Raloxifene inhibits the intestinal absorption of T4.
The original article. Siraj ES, Gupta MK, Reddy SS. Raloxifene causing malabsorption of levothyroxine. Arch Intern Med 2003;163:1367-70.
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