Gynaecomastia associated with cimetidine.

Abstract

Gynecomastia has occurred unilaterally or bilaterally in 5 out of 25 male duodenal ulcer patients after more than 4 mo. treatment with cimetidine 1.6 g daily. All elected to continue treatment to 12 mo. and their breast enlargement regressed rapidly and disappeared after stopping treatment. During treatment all patients were found to have normal concentrations of plasma testosterone and estradiol, and serum prolactin was normal in the 2 patients measured. Excision biopsy of the subareolar tissue in 1 patient revealed histology typical of the florid stage of gynecomastia. Blockade of androgen-responsive receptors in the target organ appears to be the most likely mechanism involved.