Opiates and opioids: What a difference a name makes

Abstract

We often note the conflation of the words opiate and opioid in the medical literature. Surprisingly, we occasionally note it in the pages of this journal. In some articles, opiate is used consistently—but incorrectly— throughout the text. In other articles, opiate and opioid appear to be used interchangeably—and incorrectly— throughout the text, sometimes even within the same sentence. At times, opioid in the authors’ primary source metamorphoses to opiate in the text of their manuscript. Our impression is that many authors consider these words as equivalents. In actuality, they have distinct meanings, and these meanings have clinical importance. Opiates, in the most correct sense, refer specifically to substances extracted from the milky latex of ripening pods of the opium poppy, Papaverum somniferum. Important opiate alkaloids can be divided into two major classes. Phenanthrenes comprise analgesics and their precursors that bind to opioid receptors in the nervous system. They include morphine and codeine as well as thebaine, an alkaloid without intrinsic analgesic properties, but which serves as an intermediate in the in vivo biosynthesis of morphine and codeine. Thebaine is also an important precursor for the industrial manufacture of semisynthetic pure opioid receptor agonists (eg, oxycodone, oxymorphone), opioid receptor agonists/ antagonists (eg, buprenorphine, nalbuphine), and pure opioid receptor antagonists (eg, naloxone, naltrexone). Benzylisoquinolones comprise substances that show no affinity for opioid receptors. They include, for example, papaverine, used therapeutically as a smooth muscle relaxant, and noscapine, an antitussive and currently the object of preclinical research as an antineoplastic agent. Opioids, a broader category of drugs, encompass substances of widely disparate chemical structures, which nevertheless share some degree of agonist activity at one or more of the body’s opioid receptors. Thus, opioids comprise (some) opiates and their semisynthetic derivatives, entirely synthetic compounds (eg, the fentanils, meperidine, methadone), and a variety of peptides known as endogenous opioids (eg, enkephalins, endorphins, dynorphin). This distinction is not academic quibbling. In the field of clinical urine drug testing, evidence indicates that conflation of opiate and opioid may contribute to serious errors in the application and interpretation of opiate