Dayquil

**Semantic type:** Pharmacologic Substance

**Definition:** A daytime non-drowsy preparation used to relieve common cold and flu symptoms. Dextromethorphan, one of the active ingredients, exerts its activity by raising the threshold for coughing in the cough center. Another ingredient of Dayquil, phenylephrine, a post-synaptic alpha-adrenergic receptor agonist, induces vasoconstriction, and thereby reduces blood flow, decreases swelling and prevents nasal and sinus congestion.