Green’s Dictionary of Slang

(drugs) a combination of Doriden and Tylenol 4 or Codeine 4.

1981		in Spears Sl. and Jargon of Drugs and Drink (1986).
1995		J. Stahl Permanent Midnight 28: Loads — a lethal combination of Codeine 4’s and Doriden, a potent sleep aid [...] Dors ’n’ fours, as some still called them.
2001		ONDCP Street Terms 8: Dors and 4’s — Combination of Doriden and Tylenol 4.