cold turkey

Short definition from Wiktionary

Noun

1. 1
   Sudden and complete withdrawal from a dependent substance, especially a drug.
2. 2
   The physiological effects of such a withdrawal.
3. 3
   Something exposed as a target due to surmountable defense.

Adverb

1. 1
   Not gradually; all at once. Refers especially to quitting a habit by force of will rather than by a gradual reduction.

Verb

1. 1
   To undergo sudden and complete withdrawal from a dependent substance, especially a drug.