Opioid tolerance: Symptoms

The textbook definition for drug tolerance is as follows “the need for increasing doses to maintain a defined pharmacodynamic effect.” What this means clinically is the development of shortened duration and decreased efficacy of certain opioid effects such as analgesia, central nervous system depression, and euphoria. These patients will also experience an increase in the lethal dose of these medications; however, the lethal dose of an opioid increases to a lesser extent than the effective dose, leading to a more narrow therapeutic window. Of note tolerance to constipation and miosis rarely develop, and tolerance to CNS depression and nausea appear to develop very slowly.