Publisher Summary This chapter presents an overview of methylenedioxymethamphetamine (MDMA) and discusses several case studies explaining the adverse effects of MDMA on the cardiovascular, respiratory, and nervous systems. Adverse effects can develop after amphetamines are abused in combination. An MDMA-related psychiatric adverse effect may be enhanced by a serotonin re-uptake inhibitor (SSRI). The chapter also presents the effects of cocaine on the cardiovascular, respiratory, and nervous systems. An assessment of smooth pursuit eye movements is valuable in the study of neurophysiological effects of a variety of clinical and subclinical disorders. Among women of childbearing age, cocaine abuse continues to be a major problem. One of the serious medical conditions linked with cocaine use during pregnancy is premature delivery, with an incidence in cocaine users of 17–27%. The chapter discusses the second-generation effects of cocaine usage and also reviews the immunological and hypersensitivity reactions associated with marijuana.