Dextromethorphan shows efficacy in experimental pain (nociception) and opioid tolerance.

The oral antitussive dextromethorphan is a clinically available N-methyl-D-aspartate receptor antagonist. Dextromethorphan has analgesic efficacy in the experimental formalin test, blocks the nociceptive activation of the immediate-early gene, c-fos proto-oncogene, and prevents and reverses the development of opiate analgesic tolerance in experimental models. These data suggest that dextromethorphan should be evaluated in a controlled clinical trial for analgesic efficacy in zoster-associated neuralgia.