Dimestrol (Diethylstilbestrol, DES) is a synthetic nonsteroidal estrogen. It was prescribed to pregnant women between 1940 and 1971 to prevent miscarriage, premature labor, and related complications of pregnancy. The use of DES declined after studies in the 1950s showed that it was not effective in preventing these problems. In 1971, the FDA issued a warning that risk of clear cell adenocarcinoma of the vagina and cervix was elevated in young women whose mothers used DES during pregnancy.