Thalidomide is an especially chilling example of a new medical treatment that did more harm than good.  This sleeping pill was introduced in the late 1950s as an apparently safer alternative to the barbiturates that were regularly prescribed at that time; unlike barbiturates, overdoses of thalidomide did not lead to coma. Thalidomide was especially recommended for pregnant women, in whom it was also used to relieve morning sickness.
Then, at the beginning of the 1960s, obstetricians began to see a sharp increase in cases of severely malformed arms and legs in newborn babies. This previously rare condition results in such extremely shortened limbs that the hands and feet seem to arise directly from the body. Doctors in Germany and Australia linked these infant malformations with the fact that the mothers had taken thalidomide in early pregnancy. 
A tragic epidemic of blindness in babies
Another example of unexpected harmful effects of introducing new treatments without proper evaluation of their effects.
The thalidomide tragedy stunned doctors, the pharmaceutical industry, and patients, and led to a worldwide overhaul of the process of drug development and licensing.