Coprin is a combination of three types of medicines: an antitussive, decongestant, and antihistamine. Dextromethorphan is a non-narcotic medicine that helps suppress coughing by acting on the brain’s cough center. Although similar to morphine, Coprin doesn’t cause pain relief, addiction, or much drowsiness. Pseudoephedrine (Phenylephrine) is a decongestant that shrinks the blood vessels in the nose to reduce stuffiness caused by the common cold, flu, or allergies. Triprolidine is an antihistamine that helps reduce allergy symptoms like itchy eyes, runny nose, and sneezing. Coprin may cause mild drowsiness and helps dry up watery eyes and runny nose by blocking a natural substance in the body called acetylcholine.