a.d., n.² — Green’s Dictionary of Slang

a.d. n.²

also ad, add

[reversed abbr., in order to avoid confusion with the law’s DA, a district attorney; also simple abbr. of SE addict]

(US drugs) a drug addict.

1938		D. Maurer ‘Argot of the Und. Narcotic Addict’ Pt 2 in AS XIII:3 180/1: ad or add. A narcotic addict, especially a needle-addict.
1953		Anslinger & Tompkins Traffic In Narcotics 303: A.D. A drug addict.
1955		H. Braddy ‘Narcotic Argot Along the Mexican Border’ in AS XXX:2 85: AD. (Add.), n. A narcotic addict, especially a needle addict.
1960, 1975		Wentworth & Flexner DAS.
1971		E.E. Landy Underground Dict. (1972).
1986		Spears Sl. and Jargon of Drugs and Drink.
2001		ONDCP Street Terms 1: Ad — [...] drug addict.