A longitudinal study of cotinine in long-term daily users of e-cigarettes

Drug Alcohol Depend. 2016 Mar 1;160:218-21. doi: 10.1016/j.drugalcdep.2016.01.003. Epub 2016 Jan 14.


Background: It is not clear whether, in established vapers, cotinine levels remain stable or change over time.

Methods: We enrolled 98 exclusive users of e-cigarettes on websites and forums dedicated to smoking cessation and to e-cigarettes. We collected saliva vials by mail in 2013-2014 (baseline), and collected a second saliva vial eight months later (follow-up) in the same participants. Participants had not used any tobacco or nicotine medications in the previous five days. Cotinine in saliva was analyzed with liquid chromatography-mass spectrometry. Use of e-cigarettes, tobacco and nicotine medications was self-reported.

Results: All participants were former smokers, and 99% were using e-cigarettes daily. They had already been using e-cigarettes for nine months on average at baseline. The median cotinine level was 252ng/mL at baseline (quartiles: 124-421ng/mL) and 307ng/mL at follow-up (114-466ng/mL, W=0.9, p=0.4 for change over time). The median concentration of nicotine in refill liquids was 11mg/mL at baseline (quartiles: 6-15mg/mL) and 6mg/mL at follow-up (5-12mg/mL) (Wilcoxon signed rank test: W=5.2, p<0.001 for change over time). The median volume of e-liquid used per month was 80mL at baseline (quartiles: 50-130mL) and 100mL at follow-up (60-157mL, W=3.3, p=0.001 for change over time).

Conclusion: In experienced e-cigarette users enrolled online, cotinine levels were similar to levels usually observed in cigarette smokers. Over time, these users decreased the concentration of nicotine in their e-liquids, but increased their consumption of e-liquid in order to maintain their cotinine levels constant.

Keywords: Cotinine; E-cigarette; Electronic-cigarette; Nicotine; Tobacco.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cotinine / analysis*
  • Electronic Nicotine Delivery Systems*
  • Female
  • Follow-Up Studies
  • France
  • Humans
  • Longitudinal Studies
  • Male
  • Middle Aged
  • Nicotine / analysis
  • Saliva / chemistry
  • Smoking / metabolism*
  • Smoking Cessation / methods*
  • Switzerland
  • Time Factors
  • Tobacco Use Disorder / metabolism
  • Tobacco Use Disorder / therapy
  • United States


  • Nicotine
  • Cotinine