Effects of cimetidine on thyroid hormones.

Short-term administration of the H2-antagonist cimetidine (400 mg three times/day for 5 days) was performed in eight healthy male volunteers and its effects on both thyroid hormone levels and on hypophyseal hormone release induced by acute hypoglycaemia and TRH were tested. Absolute values of basal and post-TRH serum T3 were decreased by treatment, while basal and stimulated serum rT3 and T4 levels were not altered significantly. Cimetidine administration did not change the hormone release induced by acute hypoglycaemia but significantly enhanced the prolactin and TSH responses to TRH. Our results suggest that cimetidine administration can modify the peripheral metabolism rather than the secretion of thyroid hormones.