DES (diethylstilbestrol) — the Useless Pregnancy Estrogen That Gave Daughters Vaginal Cancer

When the U.S. Food and Drug Administration issued its Drug Bulletin on 25 November 1971 declaring diethylstilbestrol contraindicated in pregnancy, it was retracting an indication it had blessed twenty-four years earlier for a drug that had never been shown to work — and the trigger was not a failure of efficacy but a cancer in a generation that had been exposed before birth. DES, the first orally active synthetic estrogen, was synthesized in 1938 in the Middlesex Hospital laboratory of Sir Edward Charles Dodds in London, deliberately left unpatented, and promoted from the mid-1940s by the Harvard husband-and-wife team of George and Olive Smith as a means of preventing miscarriage by “building up” placental hormones. The gap between that promise and the documented record is among the widest in pharmaceutical history: the drug did not prevent miscarriage, and it carried a harm that would not become visible for roughly two decades.

The signal arrived in April 1971, when Arthur Herbst, Howard Ulfelder, and David Poskanzer published a case-control study in The New England Journal of Medicine reporting eight cases of clear-cell adenocarcinoma of the vagina in young women aged 15 to 22 — a tumor so rare in that age group that a cluster of eight was itself an anomaly. Seven of the eight mothers had taken DES while pregnant; only one of thirty-two matched controls had. The association was overwhelming, with the odds of chance occurrence below one in one hundred thousand. The mechanism was transplacental: a drug given to the mother had reached across the placenta and altered the developing reproductive tract of the fetus, with the consequence emerging only at puberty.

The verdict is therefore plain at the outset. An estimated five to ten million Americans — pregnant women and the children born of those pregnancies — were exposed to DES between roughly 1940 and 1971 on the strength of an indication that controlled trials had already shown to be useless. As early as 1953, William Dieckmann’s randomized, double-blind study at the University of Chicago Lying-In Hospital had demonstrated that DES did not reduce miscarriage, premature birth, or neonatal death; prescribing continued for eighteen more years regardless. The drug was not so much a wonder therapy that went wrong as an unproven one that was never stopped.

What remains is a two-generation injury with a long tail. DES daughters carry roughly forty times the baseline risk of clear-cell adenocarcinoma, develop it at a rate near 1 in 1,000, and face elevated rates of infertility, ectopic pregnancy, premature delivery, and breast cancer; DES sons and even a third generation have shown reproductive anomalies. The episode became the founding case study of the transplacental carcinogen and a standing rebuke to the idea that a drug’s safety can be judged only in the patient who swallows it.