Green’s Dictionary of Slang

loop v.1

[SE loop, i.e. one’s drunken meandering]

(US) to go on a drinking spree; thus on a loop.

[UK](con. 1917–18) J.M. Saunders Wings (1928) 161: There was no doubt that Johnny was on a loop.
[US]E. Wilson I Thought of Daisy 67: So there was nothing to do but go looping again—I was plastered for a week.