Green’s Dictionary of Slang

cold turkey n.

[? the image of the pallid flesh of a cold, dead, plucked turkey, and a withdrawing addict; cold turkey is the ‘word of 1922’ in David K. Barnhart and Allan A. Metcalf America in So Many Words (1999)]
[1920s+] (orig. US drugs)

1. sudden and total withdrawal from heroin addiction without tapering off or using any assistance from medication; also ext. to other drugs; attrib. use slightly earlier (see sense 2).

2. attrib. use of sense 1.

3. the fundamental level, the basic situation.

4. an easy target, a vulnerable person.