Green’s Dictionary of Slang

1. (drugs) heroin.

1935		A.J. Pollock Und. Speaks n.p.: Harry, cocaine.
1953		Anslinger & Tompkins Traffic In Narcotics 309: Harry. Heroin.
1957		Kerouac letter 10 Dec. in Charters II (1999) 89: Don’t flog your dummies, and save some girls for me, and some harry.
1969		R.R. Lingeman Drugs from A to Z (1970).
1973		E. Droge Patrolman 167: Whether you call it horse [...] boy, Harry, or Scot, it’s still heroin.
2001		ONDCP Street Terms 11: Harry — Heroin.
2001		D. Looser Boobslang [U. Canterbury D.Phil. thesis] 85/1: Harry n. heroin.
2003		‘Worksheet 9: Self study of drug abuse’ St Alban’s College 🌐 Opiates e.g. [...] heroin (smack, H, horse, herries, tar, Harry China snow).
2004		Eble Campus Sl. Apr. 3: Harry Jones – heroin.

2. (UK drugs) Indian hemp, i.e. cannabis.

1961

T. Taylor Baron’s Court All Change (2011) 29: ‘He was inspired all right: Harry was with him strong!’.