Drug Abuse of Heroin and Other Opioids
- Biomolecular mechanisms of action
- Clinical pharmacology
- Clinical complications
Opioids, including naturally occurring alkaloids (opiates derived from the poppy plant Papaver somniferum), semisynthetic compounds (chemically altered alkaloids), and synthetic agents, are potent analgesics and produce an intense euphoria associated with nausea; drowsiness; miosis; and a decrease in respiration, pulse, and blood pressure. Opioids also are valued for their calming, antitussive, and antidiarrheal properties. Depending on the particular effect on opioid cell membrane receptors, they may be classified as agonists (morphine, heroin, methadone), partial agonists-antagonists (buprenorphine), or antagonists (naloxone, naltrexone). These drugs have led to many medical complications because of their abuse potential and their parenteral route of administration.
[...] Biomolecular Mechanisms of Action Opioids exert their effects on specific receptors for three distinct families of endogenous opioid peptides: enkephalins, endorphins, and dynorphins. In the central nervous system, three major classes of opioid receptors with unique selectivity and pharmacologic profiles have been identified: µ, and d. Subtypes of these major classes (µ1, µ2, d1, d2) have been elucidated primarily by the use of selective receptor antagonists. µ receptor activity is associated with the most prominent manifestations of morphine and heroin: respiratory depression, analgesia, euphoria, and the development of dependence. [...]
[...] In addition to these effects on opioid receptors, heroin causes the release of histamine, which may result in itching, scleral injection, and hypotension. High levels of tolerance develop rapidly with regard to respiratory depression, analgesia, sedation, vomiting, and euphoric properties. Little tolerance develops for miosis or constipation, so a heroin addict with an acutely painful medical condition may complain of insufficient analgesia despite pinpoint pupils. Cross-tolerance is common among opioids. From the patient's perspective, withdrawal from heroin is a dreaded clinical condition, a mix of emotional, behavioral, and physical signs and symptoms. [...]