Thalidomide was originally developed to treat morning sickness in pregnant women. Its use was stopped because it was found to cause birth defects. Thalidomide is now used as a treatment for cancer but it must not be taken in pregnancy.halidomide was originally developed to treat morning sickness in pregnant women. Its use was stopped because it was found to cause birth defects. Thalidomide is now used as a treatment for cancer but it must not be taken in pregnancy.