However, the addition of an "extremely low" dosage of 0.1 mg/day DES to cyproterone acetate has been found to result in a synergistic antigonadotropic effect and to suppress testosterone levels into the castrate range in men. DES at 3 mg/day has similar testosterone suppression to a dose of 300 mg/day, suggesting that suppression of testosterone levels is maximal by 3 mg/day. Other activities
In addition to the ERs, an in vitro study found that DES also possesses activity, albeit relatively weak, at a variety of other steroid hormone receptors. Whereas the study found EC50 values of 0.18 nM and 0.06 nM of DES for the ERα and ERβ, respectively, the medication showed significant glucocorticoid activity at a concentration of 1 μM that surpassed that of 0.1 nM dexamethasone, as well as significant antagonism of the androgen, progesterone, and mineralocorticoid receptors (75%, 85%, and 50% inhibition of positive control stimulation, respectively, all at a concentration of 1 μM). It also showed approximately 25% inhibition of the activation of PPARγ and LXRα at a concentration of 10 μM. The researchers stated that, to the best of their knowledge, they were the first to report such actions of DES, and hypothesized that these actions could be involved in the clinical effects of DES, for instance, in prostate cancer (notably in which particularly high dosages of DES are employed).
The recommended regimen started at 5 mg per day in the seventh and eighth weeks of pregnancy (from first day of last menstrual period), increased every other week by 5 mg per day through the 14th week, and then increased every week by 5 mg per day from 25 mg per day in the 15th week to 125 mg per day in the 35th week of pregnancy. DES was originally considered effective and safe for both the pregnant woman and the developing baby. It was aggressively marketed and routinely prescribed. Sales peaked in 1953. In the early 1950s, a double-blind clinical trial at the University of Chicago assessed pregnancy outcomes in women who were assigned to either receive or not receive DES. The study showed no benefit of taking DES during pregnancy; adverse pregnancy outcomes were not reduced in the women who were given DES. By the late 1960s, six of seven leading textbooks of obstetrics said DES was ineffective at preventing miscarriage.Despite an absence of evidence supporting the use of DES to prevent adverse pregnancy outcomes, DES continued to be given to pregnant women through the 1960s. In 1971, a report published in the New England Journal of Medicine showed a probable link between DES and vaginal clear cell adenocarcinoma in girls and young women who had been exposed to this drug in utero. Later in the same year, the FDA sent an FDA Drug Bulletin to all U.S. physicians advising against the use of DES in pregnant women.