APA Dictionary of Psychology

n. a synthetic opioid used clinically as a cough suppressant. Its mechanism of action is unknown, but it does bind to NMDA receptors and to sigma receptors. Dextromethorphan is a common ingredient in over-the-counter cough and cold preparations and is increasingly a drug of abuse, particularly among adolescents. Because it is metabolized extensively by the cytochrome P450 (CYP) 2D6 liver enzyme, it is used in pharmacology as a comparison when calculating the degree to which certain drugs inhibit CYP enzymes. It should not be taken by individuals who are taking monoamine oxidase inhibitors, and it should be used with caution by those taking inhibitors of the CYP2D6 enzyme (i.e., fluoxetine, paroxetine) because unexpectedly high plasma concentrations of either drug may occur (see enzyme inhibition). Examples of some common U.S. proprietary products that include dextromethorphan are Coricidin, NyQuil, Robitussin, Tylenol PM, and Vicks 44. Dextromethorphan is also used in combination with quinidine to treat pseudobulbar affect (U.S. trade name: Neudexta).