Dienestrol (INN, USAN) (brand names Ortho Dienestrol, Dienoestrol, Dienoestrol Ortho, Sexadien, Denestrolin, Dienol, Dinovex, Follormon, Oestrodiene, Synestrol, numerous others), also known as dienoestrol (BAN), is a synthetic nonsteroidal estrogen of the stilbestrol group which is or was used to treat menopausal symptoms in the United States and Europe.[1][2][3][4] It has been studied for use by rectal administration in the treatment of prostate cancer in men as well.[5] The medication was introduced in the U.S. in 1947 by Schering as Synestrol and in France in 1948 as Cycladiene.[4] Dienestrol is a close analogue of diethylstilbestrol.[6] It has approximately 223% and 404% of the affinity of estradiol at the ERα and ERβ, respectively.[7]