This medicine was developed in the 1950's as a sleeping pill. This was before standards were agreed for testing new medicines essentially testing on pregnant animals were not carried out. The drug was then discovered to prevent morning sickness.
Tragicaly the drug was not safe for developing fetuses and effected the fetuses of many who took the drug in the early stages of pregnancy. They were born with severe limb deformitites.
The tradgedy led to a new law being passed to set standards for all new medicines. The Medicines Act 1968 said all new medicines must be tested on animals to see if they will have a effect on developing fetuses.
Later it was discovered to treat leprosy and many doctors shared it in the developing world. The drug again led to deformed children and got banned by the world health organisation.
However doctors are finding more uses for the drug such as autoimmune diseases and some cancers. Although the use of the drug is now heavily monitered and never given to anyone who may become or is pregnant.