Absence of progestational activity of oral spironolactone.

Menstrual irregularity is a recognized side effect of spironolactone when used as a treatment for hirsutism in women. This effect has been attributed to the progestational activity of spironolactone observed in animal models. However, when oral spironolactone was given to women with appropriately estrogen-primed endometrium, secretory transformation of the endometrium was absent in comparison with control cycles. When control cycles were repeated with the addition of spironolactone, a decidualized endometrial response was seen. These findings suggest that spironolactone at clinically used dosages does not act as a progestin or an antiprogestin on the human endometrium.