Birth defects are part of the human condition having been observed through out history. Major birth defects, typically defined as those that are life threatning, require major surgery, or present a significant ability, affect appx. 3-4% of live born infants. Major malformations are of lesser clinical importance, and estimates of their prevalence vary considerably because of substantial differences in def. nad detection. Teratogenesis is unique kind of adv.drug effect, since it affects an organism other than the one for whom the drug was intended. A note about non prescription drugs: non prescription (OTC) drugs present a unique situation. whatever caution physician might exercise in their prescribing of drugs to pregnant women, they have little control over what consumers purchase over the counter or obtain from their friends, relatives and neighbours. It can reasonably be assumed that women, like physicians, perceive non prescription drugs, and therefore may be more willing to use OTC agents in pregnancy.