One goal of pharmacology is to break a cycle of pain and spasms. In this cycle, pain leads to muscle spasms, and spasms lead to pain with no physiologic feedback control occurring. A second goal is to break another interacting cycle of pain and inflammation. In this cycle, pain mediators can lead to inflammation and the inflammation itself can contribute to pain. The two cycles perpetuate each other because they have many interacting factors in common. Drugs are useful either alone or to supplement other forms of therapy that can break the pain/spasm cycle, as well as the pain/inflammation cycle. This article discusses the many types of drugs available to the clinician today. Although the original version of this article was published by the first author in 1973, the number of new drugs (including some new classes of agents) and newer concepts of pain that have been introduced have required further updating.