This article describes research about reducing cigarette smoking in your sleep. The study in the article involves using a psychological concept of learning called respondent conditioning - think of Pavlov and his dog, at outlined in this Wikipedia article. The study participants were all smokers who expressed desire to quit. Researchers paired the smell of cigarettes with a foul odor when participants were asleep. Supposedly, the participants unconsciously associated the foul smell with the smell of cigarettes and ended up smoking 30% less. There was no smoking reduction in participants that were exposed only to cigarette smoke when asleep or if the participants were exposed to both smells, but while awake.
Two other interesting points about this study. The first one is that the participants did not remember the smells they were exposed to in their sleep. Also, it appeared that a light stage of non-dream sleep was was the most effective stage of sleep that was associated with reduced smoking. The authors concluded that conditioning can occur in sleep and that this technique may be used in other addictions.