Green’s Dictionary of Slang

piped adj.1

1. (US) drunk [SE pipe, a large barrel].

[US]Number 1500 Life In Sing Sing 251: Pipe. person under the influence of intoxicants.
[US]Anaconda Standard (MT) 20 Jan. 21/6: [P]iped to the gills.
[US]Ade Knocking the Neighbors 98: He was keyed to Concert Pitch and the Audience was Piped and all the old sure-fire Bokum of a Sentimental Nature simply Killed them.
[US]G. Henderson Keys to Crookdom 413: Piped – under the influence of liquor.
[US] ‘Sl. Expressions for Drunk’ in New Republic in AS XVI:1 (1941) 9 Mar. 70: [...] piped.

2. (also piped up) in drug uses [pipe n.1 (3)].

(a) under the influence of drugs.

[US]G. Henderson Keys to Crookdom 413: Piped – under the influence of [...] narcotics.
[US]Monteleone Criminal Sl. (rev. edn).
[US]Anslinger & Tompkins Traffic In Narcotics 313: piped. Under the influence of drugs.
[US]J. Stahl I, Fatty 115: A half-dead junkie [...] who shuffled like a piped-up Chinaman.

(b) under the influence of crack cocaine.

[US]R. Shell Iced 38: I remember things I have done to get piped.