CHAPTER 22: Morphine, Heroin and Other Opiates

Along with other plant-based drugs such as cannabis and cocaine, opium has long been under international control. Morphine is the principal active alkaloid in opium and typically comprises 10% of the dried latex. Diamorphine (diacetylmorphine) is a semi-synthetic product obtained by acetylation of morphine. The attraction of diamorphine is that it has a higher lipophilicity and is able to penetrate the blood–brain barrier more efficiently than morphine. Morphine and 6-monoacetylmorphine rapidly formed in vivo from diamorphine, behave as agonists at a complex group of receptors (the µ, κ and δ sub-types) that are normally acted upon by endogenous peptides known as endorphins. Apart from analgesia, diamorphine produces drowsiness, euphoria and a sense of detachment. Negative effects include respiratory depression, nausea and vomiting, decreased motility in the gastrointestinal tract, suppression of the cough reflex and hypothermia. Heroin is a crude preparation of diamorphine that contains other opium alkaloids and is the leading cause of drug-associated fatalities in many countries. Alkaloids derived from opium as well as synthetic compounds that are largely based on the benzofuroisoquinoline skeleton are termed opiates; many have been used for medicinal purposes. Other narcotic analgesics that are structurally-unrelated to morphine are known as opioids.