A systematic review of refillable e-liquid nicotine content accuracy.

Objectives The use of e-cigarettes is becoming more common in the United States. E-cigarettes are often refilled with nicotine-containing solutions of various concentrations purchased in local shops or on the Internet. There is evidence that the nicotine content in these solutions is often mislabeled; thus, we reviewed the available literature on this topic. Data sources We conducted a systematic review of peer-reviewed articles published worldwide on e-liquid nicotine content accuracy using the databases CAB Direct, Cochrane Central Register of Controlled Trials, PubMed, and SPORTDiscus (EBSCO). Study selection Initial screening of titles and abstracts was conducted to determine relevancy for inclusion. Full-article reviews of studies involving the purchase and chemical analysis of nicotine content in refillable e-liquids were conducted for final inclusion. Data extraction Data extraction included e-liquid sample size, whether the samples were labeled to contain nicotine, whether the samples were purchased in retail shops or online, and the number and percentage of samples where the analyzed nicotine content fell outside 10% of the labeled nicotine content. Results Twenty articles described cross-sectional studies of purchased samples containing nicotine. The number of nicotine-containing e-liquid samples obtained in each study varied from 2 to 71. The percentage of samples with an analyzed nicotine concentration of more than 10% above or below the labeled nicotine concentration ranged from 0% to 100% (overall 278/574 or 48.4%; median 46.85%). A large percentage of the samples deviated by 10% from the labeled nicotine concentrations in both U.S. and non-U.S. samples, with U.S. samples having a higher percentage. Conclusion Our review shows that actual nicotine concentrations in e-liquids may vary considerably from labeled concentrations. Pharmacists should warn patients to be wary of the contents of e-cigarettes, and explain the dangers of using these products.