Green’s Dictionary of Slang

(UK black/W.I.) intoxicacted by marijuana; thus frass out, to collapse under the influence of the drug .

2013		Jamican Patwah Dict. 🌐 Mi tek two draw adi chalice and mi frass.
2020		G. Krauze What They Was 63: Not Nice and Kane [...] just frass out on one of the spare sofas .