Treatment-seeking adults (aged 18–65) smoking ≥10 cigarettes per day for the past six months responded to advertisements for a smoking cessation clinical trial (NCT01314001). Exclusion criteria included the use of chewing tobacco, snuff or snus; recent treatment for substance abuse; current cocaine or opiate abuse; the consumption of >25 standard alcoholic drinks/week; current depression, mania, schizophrenia, or post-traumatic stress disorder; recent use of anti-psychotics, anti-depressants, prescription stimulants, metformin, cimetidine, cardiac medications, or other anti-coagulants; and the daily use of prescription opiates/inhalers. Those interesting in participating after meeting eligibility criteria provided a blood sample for NMR determination, collected when participants were smoking as usual. The detailed study protocol, including NMR determination, is described in a previous analysis of NMR and three self-report measures of nicotine dependence in a subset of the trial participants (N=833 of 1807 screened by NMR) [19 ]. Briefly, cotinine and 3′hydroxycotinine were assessed from whole blood by liquid chromatography-tandem mass spectrometry (LC/MS-MS) using a previously validated method [41 , 42 (link)]. NMR data were available on a total of 1807 eligible participants screened at the four clinical sites: the University of Pennsylvania (N=487), the Centre for Addiction and Mental Health (CAMH) at the University of Toronto (N=430), the MD Anderson Cancer Center (N=443) and the University at Buffalo, SUNY (N=447). Survey data on demographic variables (including age, gender, ethnicity) and smoking history were collected, as well as height and weight measurements in order to compute BMI. Data were also collected from female participants on the use of oral contraceptives and hormone replacement therapies. Data on mentholated cigarette use was collected from the subset of participants in the intent-to-treat (ITT) group (N=1155), assessed when they received their study medication and completed the first counseling session. Informed consent was obtained from each participant. The study was approved by Institutional Review Boards at each site.