dextromethorphan + diphenhydramine

**dextromethorphan + diphenhydramine** is a fixed-dose combination of two small-molecule drugs commonly used in over-the-counter medications for the symptomatic relief of cough and other cold or allergy symptoms. - **Dextromethorphan** is an antitussive that acts on the central nervous system to suppress the cough reflex by modulating the activity of the sigma-1 and NMDA glutamatergic receptors in the brain, thereby decreasing the urge to cough. - **Diphenhydramine** is a first-generation antihistamine that blocks histamine H1 receptors, leading to relief from symptoms related to histamine release, such as sneezing, runny nose, and watery eyes, and also provides sedative and anticholinergic effects[2][4][6]. This combination is primarily used for acute cough, runny nose, sneezing, and related symptoms due to upper respiratory tract infections, colds, or allergies. Diphenhydramine contributes additional benefit by ameliorating symptoms due to allergies and by providing sedation.