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Among the remedies which it has pleased almighty God to give to man to relieve his sufferings, none is so universal and efficacious as opium.

Sir Thomas Sydenham, 1680

Opium is a heterogeneous drug derived from the milky exudate of the opium poppy, Papaver somniferum. The word opium is derived from the Greek word for juice. This natural product, which contains over 20 different alkaloids, has been used to control human discomfort for over five millennia. Opium was used clinically in the early days of European medicine, but it fell into disfavor because of toxic outcomes from nonstandardized drugs that were not used with necessary care. Paracelsus repopularized the use of opium in the 16th century, and by the second half of that century, clinical use of opium was understood and adopted by physicians throughout the continent.

The French pharmacist Jean-François Derosne isolated a crystalline precipitate from opium in 1803, but that material was a mixture of morphine and narcotine. It was not until 3 years later that the German pharmacist Friedrich Wilhelm Sertürner isolated the alkaloid morphine from opium. He named this powerful drug after Morpheus, the Greek god of dreams. Other opium alkaloids including papaverine and codeine were soon isolated, and within a few decades, the purified alkaloids began to replace crude opium in clinical practice.

Narcotic—a term derived from the Greek word meaning benumbing—was originally used to describe opium derivatives. Today, narcotic has become a legal term that includes a broad range of sedating and potentially abused drugs, many of which are not at all related to opium. Because the word narcotic has such negative connotations, clinicians should not use it when talking with patients. Opioid is the preferred term in both clinical and scientific dialogue. Opioids are literally opium-like substances. In the recent past, opioid was used primarily to describe endogenous opium-like substances, and the term opiate was used to describe drugs that are opium derivatives. The differences between exogenous opioids, such as morphine, and endogenous opioids, such as β-endorphin, do not justify differing terminology. Opioid accurately describes both types of compounds and is generally considered the preferred term today.

It is not logical that the human body should contain specific receptors for alkaloids derived from a plant. The presence of endogenous opioids was postulated to explain the presence of opioid receptors before the endogenous substances were isolated. Three distinct families of endogenous human opioid peptides, the endorphins, enkephalins, and dynorphins, have been isolated. These peptides are found within the central nervous system (CNS), adrenal medulla, nerve plexi, gastric exocrine glands, and intestines. These peptides appear to have multiple roles including modulation of pain, neurohumoral transmission, and neurohormonal effects.

Opioids remain the most effective analgesics available. They are clinically useful in treating diarrhea and gastrointestinal hypermotility because activation of opioid receptors in the intestines slows peristalsis. Opioids decrease respiratory ...

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