oats, n.³ — Green’s Dictionary of Slang

oats n.³

[rhy. sl.; oats and barley = charlie n.⁷ (1); for an earlier rhy. sl. use, playing simply on the proper name, note oats (and barley) n. (2)]

(drugs) cocaine.

2000		J.J. Connolly Layer Cake 66: The price of oats was higher then.
2011		J.J. Connolly Viva La Madness 41: I like a drop of the oats meself [...] but she’s gone silly on it.