As many as 10 million U.S. women may have used the drug between 1938 and 1971, when it was banned after being linked to vaginal cancers in daughters of women who used it.

A pregnancy drug banned decades ago may have side effects that linger for generations. Grandchildren of women who took it have an increased risk of attention deficit hyperactivity disorder (ADHD), a new study suggests.

The drug, a synthetic estrogen known as diethylstilbestrol (DES), was designed to prevent pregnancy complications like miscarriage and preterm delivery. As many as 10 million U.S. women may have used the drug between 1938 and 1971, when it was banned after being linked to vaginal cancers in daughters of women who used it.

Now, a new study suggests that grandchildren of women how took DES during pregnancy are 36 percent more likely to be diagnosed with ADHD than other kids.