I used to smoke 30 cigarettes a day. But when I got sick last winter I decided enough was enough. I stopped smoking overnight and haven’t had a cigarette since. It doesn’t work for everyone, but going cold turkey (kalter Entzug, abrupt) was the best way for me to quit.
This American idiom comes from the earliest 20th century, when it had quite a different meaning. Back then, talking cold turkey meant to talk in a direct and no-nonsense way, i.e. not beating around the bush. From there, we got the cold turkey way of quitting drugs or alcohol: no special program, just simply stopping. In modern English, this is the meaning we kept. Although talking turkey still means speaking in a direct and unprepared way.