While you are pregnant, almost everything you eat, drink, or smoke passes through your body to your baby. That's why drugs taken during pregnancy can be harmful to your baby. Legal drugs include cigarettes and alcohol. Babies whose mothers smoke during pregnancy are more likely to be small at birth or to be born too early.
Alcohol can cause mental retardation, problems with growth, and abnormal facial appearance.
Prescription medicines can also cause problems. Some prescription acne medicines can cause birth defects. So can some medicines that are used to treat seizures. The antibiotic tetracycline can cause changes in the baby's teeth and bones if taken late in pregnancy. Tranquilizers can be addictive to the baby and the mother.