Recent research advances indicate that specialized neural pathways are involved in the encoding of pain sensations and that these pathways are sensitive to changes in stimulus features, such as intensity, quality, duration, and location. It has also been established that there are three major families of opioid peptides in the brain: the enkephalins, the dynorphins, and the endorphins. In addition to these opioid peptides, other neurochemicals such as serotonin and norepinephrine play a role in the modulation of signals related to tissue damage. These advances in research are being used to develop improved methods for the control of acute and chronic pain. Nonsteroidal anti-inflammatory drugs suppress noxious signals by reducing the sensitization of peripheral nociceptors. Opioid drugs are administered into the membranes surrounding the spinal cord to provide long-lasting pain relief. Peripherally acting opioid drugs may represent a new functional class of analgesics devoid of the undesirable side effects of centrally acting opioids. Tricyclic antidepressant drugs are used in the treatment of neuropathic pain, based on their effects on noradrenergic and serotoninergic pathways in the central nervous system.