Systematic review of the relationship between the 3-hydroxycotinine/cotinine ratio and cigarette dependence.

Individual differences in the rate of nicotine metabolism (RNM) could be related to dependence and success in stopping smoking. A range of studies have examined RNM measured by the ratio of trans-3'-hydroxycotinine and cotinine in body fluids (the ratio). A systematic review of this literature is needed to draw conclusions and identify gaps in evidence.