The placenta was classically considered a barrier, but in 1957 this notion was shattered. This organ is only a selective filter and metabolic site. In this review, the placental transfer of the top 17 substances of abuse are analyzed. In the National Library of Medicine only 41 papers that documented placental transfer of the major substances of abuse could be located, and these data excluded approximately one-sixth of the most commonly abused substances. Nonetheless, it was possible to evaluate placental transfer of all substances of abuse based on their physical chemical properties. It is with despair that it must be reported that virtually all substances of abuse freely cross the placenta, exposing the embryo/fetus to whatever substances the mother may be using.