Diethylstilbestrol (DES), also known as stilbestrol or stilboestrol, is a nonsteroidal estrogen medication, which is presently rarely used. In the past, it was widely used for a variety of indications, including pregnancy support for women with a history of recurrent miscarriage, hormone therapy for menopausal symptoms and estrogen deficiency in women, treatment of prostate cancer in men and breast cancer in women, and other uses. By 2007, it was only used in the treatment of prostate cancer and breast cancer. In 2011, Hoover and colleagues reported on adverse health outcomes linked to DES including infertility, miscarriage, ectopic pregnancy, preeclampsia, preterm birth, stillbirth, infant death, menopause prior to age 45, breast cancer, cervical cancer, and vaginal cancer. While most commonly taken by mouth, DES was available for use by other routes as well, for instance, vaginal, topical, and by injection. DES is an estrogen, or an agonist of the estrogen receptors, the biological target of estrogens like estradiol. It is a synthetic and nonsteroidal estrogen of the stilbestrol group, and differs from the natural estrogen estradiol in various ways. Compared to estradiol, DES has greatly improved bioavailability when taken by mouth, is more resistant to metabolism, and shows relatively increased effects in certain parts of the body like the liver and uterus. These differences result in DES having an increased risk of blood clots, cardiovascular issues, and certain other adverse effects.DES was discovered in 1938 and introduced for medical use in 1939.
A 3 mg/day dosage of DES has been associated with an incidence of thromboembolism of 9.6 to 17%, with an incidence of cardiovascular complications of 33.3%. A lower dosage of 1 mg/day DES has been associated with a rate of death due to cardiovascular events of 14.8% (relative to 8.3% for orchiectomy alone). Other long-term effects
DES has been linked to a variety of long-term adverse effects, such as increased risk of 

vaginal clear-cell adenocarcinoma
vaginal adenosis
T-shaped uterus
uterine fibroids
cervical weakness
breast cancer
infertility
hypogonadism
intersexual gestational defects
depression,
and others,in women who were treated with it during pregnancy, and/or in their offspring.A comprehensive animal study in 1993 found a plethora of adverse effects from DES such as (but not limited to) 

genotoxicity (due to quinone metabolite)
teratogenicity
penile and testicular hypoplasia
cryptorchidism (in rats and rhesus monkeys),
liver and renal cancer (in hamsters), ovarian papillary carcinoma (in canines), and
malignant uterine mesothelioma (in squirrel monkeys). Evidence was also found linking ADHD to F2 generations, demonstrating that there is at least some neurological and transgenerational effects in addition to the carcinogenic.Rodent studies reveal female reproductive tract cancers and abnormalities reaching to the F2 generation, and there is evidence of adverse effects such as irregular menstrual cycles intersexual in grandchildren of DES mothers. Additionally, evidence also points to transgenerational effects in F2 sons, such as hypospadias. At this time however, the extent of DES transgenerational effects in humans is not fully understood. Overdose
DES has been assessed in the past in clinical studies at extremely high doses of as much as 1,500 to 5,000 mg/day.