However, similarly to the case of prostate cancer, arguments have been made for the use of bioidentical estrogens like estradiol instead of DES for breast cancer.Oral DES at 0.25 to 0.5 mg/day is effective in the treatment of hot flashes in men undergoing androgen deprivation therapy for prostate cancer.Although DES was used to support pregnancy, it was later found not to be effective for this use. Side effects
At more than 1 mg/day, DES is associated with high rates of side effects including nausea, vomiting, abdominal discomfort, headache, and bloating (incidence of 15–50%). Breast changes and feminization
The pigmentation of the breast areolae are often very dark and almost black with DES therapy. The pigmentation that occurs with synthetic estrogens such as DES is much greater than with natural estrogens such as estradiol. The mechanism of the difference is unknown. Progestogens like hydroxyprogesterone caproate have been reported to reduce the nipple hyperpigmentation induced by high-dose estrogen therapy.In men treated with it for prostate cancer, DES has been found to produce high rates of gynecomastia (breast development) of 41 to 77%. Blood clots and cardiovascular issues
In studies of DES as a form of high-dose estrogen therapy for men with prostate cancer, it has been associated with considerable cardiovascular morbidity and mortality. The risk is dose-dependent. A dosage of 5 mg/day DES has been associated with a 36% increase in non-cancer-related (mostly cardiovascular) deaths. In addition, there is an up to 15% incidence of venous thromboembolism.
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.