Dutasteride belongs to a class of drugs called 5α-reductase inhibitors, which block the action of the 5α-reductase enzymes that convert testosterone into DHT. It inhibits all three forms of 5α-reductase, and can decrease DHT levels in the blood by up to 98%. Common side effects include sexual problems, breast tenderness, and breast enlargement. Other side effects include an increased risked of certain forms of prostate cancer, depression, and angioedema. It was patented in 1993. Also it can prevent the formation of neurosteroid metabolites like allopregnanolone from progesterone and hence may reduce or block the sedative, anticonvulsant, anxiolytic, and various other effects of progesterone, particularly in the case of oral progesterone.