Mepyramine, also known as pyrilamine, is a first generation antihistamine, targeting the H1 receptor as an inverse agonist. It rapidly permeates the brain, often causing drowsiness.
The medication has negligible anticholinergic activity, with 130,000-fold selectivity for the histamine H1 receptor over the muscarinic acetylcholine receptors (for comparison, diphenhydramine had 20-fold selectivity for the H1 receptor).
It was patented in 1943 and came into medical use in 1949. It is used in over-the-counter combination products to treat the common cold and menstrual symptoms. It is also the active ingredient of the topical antihistamine creams Anthisan and Neoantergan sold for the treatment of insect bites, stings, and nettle rash.