Opioid analgesics are often used for the treatment of both acute and chronic pain. These agents can differ in regard to opioid receptor interactions, pharmacological actions, and side effect profiles. Furthermore, an agent can be differentiated by its relative potency and duration of action. This paper highlights the major differences between the opioid analgesics and presents a comparative table which includes equianalgesic doses for available opioid formulations. Also, guidelines for making rational prescribing decisions are discussed.