PSY 374 Study Guide - Midterm Guide: G Protein–Coupled Receptor, Opioid Receptor, Periaqueductal Gray
Document Summary
Opioid drugs are narcotic analgesics; they reduce pain (analgesic effect), and create a sense of euphoria, relaxation and sleep (narcotic effect) The main active ingredient in opium is morphine. Opium also contains codeine, thebaine, narcotine, and other ingredients. Only a small fraction of morphine crosses the blood-brain barrier (even when injected. Heroin is made by adding two acetyl groups to morphine, making it more lipid soluble; heroin reaches the brain faster than morphine, making it much more potent when injected. Other modifications produce partial agonists: they bind to the receptors but have less biological effect. Pure antagonists, such as naloxone and nalorphine, are structurally similar to morphine but have no efficacy at the opiate receptor; these drugs can prevent or reverse the effect of opioids. Partial agonists include pentazocine (talwin), nalbuphine (nubain) and buprenorphine (buprenex); these drugs are less potent than morphine when used as analgesics, but they carry less risk of respiratory depression and drug dependence compared to morphine.
