Dextromethorphan Hydrobromide (10mg) + Diphenhydramine (8mg) (Medical Monograph)

Overview

A fixed-dose combination antitussive medication containing Dextromethorphan, a centrally-acting non-opioid cough suppressant, and Diphenhydramine, a first-generation sedating antihistamine with anticholinergic and antitussive properties. This combination provides synergistic cough suppression by acting on different pathways in the cough reflex arc, offering relief from both dry, non-productive cough and associated symptoms like rhinorrhea and sneezing.

The combination works synergistically to suppress the cough reflex. Dextromethorphan acts centrally on the sigma-1 receptor and as an NMDA receptor antagonist in the medullary cough center, raising the threshold for coughing. Diphenhydramine acts both centrally and peripherally: it suppresses the cough center via its sedative/anticholinergic action and provides peripheral H1-antagonism, reducing post-nasal drip and irritation that can trigger cough.