cold turkey

/K OW1 L D T ER0 K IY0/
noun
  1. 1

    Sudden and complete withdrawal from a dependent substance, especially a drug.

  2. 2

    The physiological effects of such a withdrawal.

adverb
  1. 1

    Not gradually; all at once. Refers especially to quitting a habit by force of will rather than by a gradual reduction.

    โ€œIt is difficult, but possible to quit smoking cold turkey.โ€

Source: https://en.wiktionary.org/wiki/cold%20turkey