Green’s Dictionary of Slang

(US) intoxicated on drugs or by alcohol.

1968		J. Moura Tender Loving Care 146: They were both gooned...Penner then saw the window and vibrated his head to clear up his alcoholic vision [HDAS].
1983		National Lampoon Aug. 40: Janie [was] gooned-out on amaretto and milk [HDAS].
1993		Troll & Madsen Ray Troll’s Shocking Fish Tales 31: Consider the cultural implications of a boatload of tourists in the Bahamas gooned out on rum at ten in the morning.
2005		D. Kukoff Vault Career Guide to Screenwriting Careers 61: John Travolta’s gooned-out character, Vincent.