cold-turkey

"without preparation," 1910; narrower sense of "withdrawal from an addictive substance" (originally heroin) first recorded 1921. Cold turkey is a food that requires little preparation, so "to quit like cold turkey" is to do so suddenly and without preparation. Cf. cold shoulder.

To “go cold turkey” is to withdraw suddenly and completely from an addictive substance or some other form of dependency: “Many people who attempt to quit smoking do so by going cold turkey rather than by gradually cutting down.”

Immediate, complete withdrawal from something, especially an addictive substance; also, without planning or preparation. For example, My bad shoulder forced me to quit playing tennis cold turkey, or I'd never done any rock climbing, but decided to try it cold turkey. This term may have come from the earlier expression talk turkey (for blunt speaking). At first used strictly for abrupt withdrawal from drugs or alcohol, it soon was transferred to quitting any habit or activity. [Early 1900s]