Green’s Dictionary of Slang

heady adj.¹

drunk.

1861		(con. 1840s–50s) H. Mayhew London Labour and London Poor III 288/1: When they become heady [...] then the publicans kick our poor men out.
1915		M.G. Hayden ‘Terms Of Disparagement’ in DN IV:iii 214: heady, drunk.
2015		‘Elvis Costello’ Unfaithful Music 157: The whiskey felt warm and I was soon heady in the overheated, airless train.