Opioids

Any substance that possesses morphine-like effects is termed an opioid. These drugs have analgesic effects and can be used as an adjunct to anaesthesia. The receptors m,k, d and s are linked through G-proteins thus inhibiting adenylate cyclase, thereby reducing the pain pathways. They also facilitate the opening of K+ channels and inhibit Ca 2+ channel opening. Some opioids produce dysphoric effects such as hallucinations, anxiety and bad dreams. They also produce constipation and respiratory depression. Examples include morphine, heroin, codeine, pethidine, methadone and oxycodone.