Molecular Biology of Opioid Analgesia

Opioids provide excellent pain relief in most patients. Yet the responses of patients to individual opioids can vary markedly, even among the μ opioids. Understanding this variability would greatly enhance our ability to treat patients appropriately. Classical pharmacological studies have long implied the existence of multiple subtypes of μ opioid receptors. More recently, a number of variants of the cloned μ opioid receptor have been described. These variants all show the same selectivity for μ opioids, confirming their classification as μ opioid receptors. Yet, they differ in their functional activation by opioids as well as in their localization within cells and regions in the brain. These multiple μ opioid receptors may help explain the range of responses seen clinically among patients for the various opioid drugs.