Green’s Dictionary of Slang

(US drugs) the taking by teenagers of prescription drugs – usu. high-strength opioid painkillers – as found at home; thus pharming, stealing drugs from the family medicine cabinet.

2002		Chambersburg (PA) Public Opinion 8 Mar. 🌐 In some communities, kids have ‘pharming’ parties. They go to their parents’ or grandparents’ medicine cabinets and take whatever drugs are there. At the parties, they throw the pills in a bowl and take a handful.
2006		USA Today 13 June 🌐 A teenager in Jan Sigerson’s office mentioned a ‘pharm party’ in February [...] ‘Pharm,’ it turned out, was short for pharmaceuticals. [...] It’s a culture with its own lingo: [...] collecting pills from the family medicine chest is called ‘pharming.’.