Green’s Dictionary of Slang

(drugs) Seconal.

1969		R.R. Lingeman Drugs from A to Z (1970) 226: seccy seconal, a barbiturate [...] seggy.
1971		E.E. Landy Underground Dict. (1972) 166: seccy [...] seggy n. Seconal.
1981		D.E. Miller Bk of Jargon 338: seccy, seggy: Seconals.
2001		Observer Mag. 14 Oct. 23: Users sometimes call it Seccy, Seggs or Seggy.