Racemic thalidomide was originally introduced as a sedative and hypnotic for treatment of morning sickness in 1957, but was withdrawn from use in the early 1960s after it was shown to produce severe teratogenic effects. It was subsequently found that the (R)-enantiomer is effective against morning sickness, whereas the (S)-enantiomer is teratogenic. However, as the enantiomers can interconvert in vivo, administering only the (R)-enantomer would not prevent the teratogenic effect.