Agonists partial agonists antagonists

Among the remedies which it has pleased Almighty God to give to man to relieve his sufferings, none is so universal and so efficacious as opium (Thomas Sydenham, physician, 1680).

Opium (the dried juice of the seed head of the opium poppy) was certainly used in prehistoric times, and medical practice still leans heavily on its

26 The term opiate has been used for the natural alkaloids of opium, and opioid for other agents having similar action. The distinction is neither generally observed nor particularly useful. We here use opioid for all receptor-specific substances.

alkaloids, using them as analgesic, tranquilliser, antitussive and in diarrhoea.

The principal active ingredient in crude opium was isolated in 1806 by Friedrich Sertürner, who tested pure morphine on himself and three young men. He observed that the drug caused cerebral depression and relieved toothache, and named it after Morpheus.27

Opium contains many alkaloids, but the only important ones are morphine (10%) and codeine; papaverine is occasionally used as a vasodilator (see p. 546). Purified preparations of mixtures of opium alkaloids, e.g. papaveretum (Omnopon), are available; minus noscapine which is suspected of genotoxicity.

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