"Cold turkey" is a slang expression describing the actions of a person who gives up a habit or addiction all at once, rather than gradually (easing the process through tapering off or using supplemental medication). This is, of course, the cheapest method of quitting any habit, and its supposed advantage is that by not actively using supplemental methods, the person avoids thinking about the habit and therefore, the temptation.
The term allegedly derives from the comparison of a cold turkey carcass and the state of a withdrawing addict — most notably, the cold sweats and goose bumps. It is often preceded by the verb "to go," as in "going cold turkey."
Sudden withdrawal from drugs such as benzodiazepines and barbiturates can be extremely dangerous, leading to potentially fatal seizures. In long-time alcoholics, going cold turkey can cause life-threatening delirium tremens and thus is not an appropriate method for breaking an alcohol addiction. Although many people disagree, it has been said that nicotine cessation can be the most difficult form of cold turkey, more difficult than even heroin or cocaine.
In the case of most other drugs, going cold turkey may be extremely unpleasant, but not actually dangerous. Stopping to take a medication that has been prescribed, however, may be dangerous.