dextromethorphan + guaifenesin + doxylamine succinate

A combination drug containing **dextromethorphan**, **guaifenesin**, and **doxylamine succinate**. - **Dextromethorphan** is a **cough suppressant** that works primarily as a low-affinity, uncompetitive NMDA receptor antagonist and a sigma-1 receptor agonist; it also has additional activity as an antagonist of certain nicotinic acetylcholine receptors and weak inhibitor of serotonin and noradrenaline transporters[1][2]. - **Guaifenesin** is an **expectorant** that increases the volume and reduces the viscosity of secretions in the trachea and bronchi, facilitating the removal of mucus from the respiratory tract[3]. - **Doxylamine succinate** is a **first-generation antihistamine** (ethanolamine class), antagonizing the H1 histamine receptor, and possesses significant anticholinergic and sedative properties, which help relieve symptoms such as runny nose, sneezing, and watery eyes due to colds or allergies[3][7]. This combination is primarily used for the **symptomatic treatment of cough, chest congestion, and other upper respiratory symptoms** associated with the common cold or flu, particularly those accompanied by cough, mucus, and significant runny nose or night-time symptoms[3][7].