Norethynodrel-Mestranol and Thyroid Function

Indices of thyroid function were measured in 10 euthyroid females after equilibration to each of 3 treatments: (a) without medication, (b) while taking 250 μg thyroxine daily, and (c) while taking 250 μg thyroxine and 10 mg norethynodrel-mestranol daily. The thyroidal radioiodine clearance rate decreased from treatment (a) to treatment (b). The addition of norethynodrel-mestranol treatment (c) produced no further change in radioiodine clearance, suggesting that equilibrium thyroid function during administration of this drug is not characterized by increased TSH secretion. The extrathyroidal thyroxine space and the disappearance rate of 131I-thyroxine were higher during treatment (b) than during treatments (a) and (c), presumably because of a relatively increased free thyroxine level. Daily thyroxine utilization rates (in μg/day), however, during treatments (b) and (c) were similar and higher than the rate during treatment (a). The administration of norethynodrel-mestranol did not, therefore, alter thyroxi...