Dr. Bartalo in “Barber of Seville” (1818) hated Figaro because Figaro doped up the member’s of Dr. Bartalo’s household.
A lot of people back in that era didn't realize the danger that drugs posed. There was a famous doctor from later that century that studied the use of opioid or cocanoids for pain control, and accidentally addicted himself. He struggled with it for the rest of his life.