The story
Probably from guan- (“guanidine derivative”) + ph(enyl)ac(etyl) + -ine.
Etymology from Wiktionary, CC BY-SA 4.0.
guanfacine
Today it means: A drug that is an alpha-adrenergic agonist taken orally in the form of its hydrochloride C₉H₉Cl₂N₃O·HCl especially to treat hypertension and attention deficit disorder. It is marketed under the trademarks Intuniv and Tenex. Full definition →