Green’s Dictionary of Slang

overcome by drink and/or drugs.

1999		Guardian Weekend 19 June 22: A man who confesses to having spent ‘25 years gacked to the nines’.
2011		J.J. Connolly Viva La Madness 296: Half are clucking, the other pissed and gakked.
2021		T. Swerdlow Straight Dope [ebook] I don’t even remember that, I was so gakked on Ritalin [ibid.] I’m too gakked up to even think about dealing with it now. But I’m not too gakked to notice a business card cradled in the duffle’s bottom.