Green’s Dictionary of Slang

1. (US drugs) overcome by a drug.

1949		Monteleone Criminal Sl. (rev. edn).
1953		Anslinger & Tompkins Traffic In Narcotics 308: flogged. Under the influence of drugs.

2. exhausted.

1961		K. Williams Diaries 11 Mar. 170: I have no enthusiasm left [...] Both Sheila and I are flogged. My voice almost gone in 2nd house.
1979		J. Morrow Confessions of Proinsias O’Toole 143: A pot-addled car nut who had never before trod the pedal of anything more nippy than a flogged-out Cortina.