NICOTINE RECEPTOR SATURATION IN “NO-NICOTINE CIGARETTES”. “The researchers also looked at de-nicotinized cigarettes, which contain only a trace amount of nicotine (0.05 milligrams) … They found that even that a low nicotine level is enough to occupy a sizeable percentage of receptors.”
http://newsroom.ucla.edu/releases/do-light-cigarettes-deliver-less-64109