This chapter will explore the psychopharmacological effects of a select number of both licit and illicit drugs. The drugs that are featured in this chapter are those which are the most pertinent to the drug policies that we will be encountering in the remainder of this book. Students will learn how and why some drugs are classified as being either stimulants, depressants, or psychedelics/hallucinogens. The concept of dependence will be introduced, and this chapter will overview the similarities and differences between two types: namely; physical and psychological dependence. Lastly, this chapter will discuss how drugs can have both direct and indirect health consequences, using opiates and heroin as illustrative examples.