Why does Spironolactone cause irregular menstruation? Is it safe for family history of breast cancer?

Spironolactone, (also called Aldactone, causes irregular periods in about three quarters or more of users. The drug reduces production of steroids in the adrenal gland as well as the ovaries. It also suppresses GnRH (gonadotropin releasing hormone) in the pituitary. With this suppresses, the release of LH (luteinizing hormone) and FSH (follicle stimulating hormone) are suppressed. Why care if LH and FSH are suppressed? Well, the balance of these two hormones play a key role in the menstrual cycle. The imbalance, coupled with the reduced hormone synthesis in the ovary leads to irregular periods. Whether or not to use with a family history of breast cancer is dealt wth on a case by case basis - see your physician for guidance. 

This drug alters the hormonal balance in females that take it and if there is a history of breast cancer, this could influence the growth of a cancer, in theory