The perinatal period should be regarded as a continuum that extends from the beginning of a woman's pregnancy through delivery and the first month of a child's life. Although in this chapter we discuss discrete drugs, clinicians must be aware that the use of any psychoactive drug during pregnancy may mean that other psychoactive agents are being used concomitantly. Perinatal effects may therefore reflect pharmacological effects of individual agents or the combined effects of multiple drugs. In all cases, substance use during pregnancy must be considered to be high risk from general medical, obstetric, neonatal, pediatric, and psychosocial standpoints. It is extremely important, however, to recognize that providing comprehensive, supportive, nonjudgmental care for the pregnant woman and her family in a well-integrated, multidisciplinary setting offers a unique opportunity to restructure the woman's life in a positive direction.