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Adolescents and young adults have difficulty understanding nicotine concentration labels on vaping products presented as mg/ml and percent nicotine.

INTRODUCTION
E-cigarette/e-liquid nicotine concentrations typically are labeled as mg/ml or percent nicotine. We examined whether these metrics accurately convey nicotine strength to young e-cigarette users and if youth can compare concentrations presented in mg/ml and percent nicotine.


METHODS
821 adolescent and young adult e-cigarette users participated in the survey. Participants rated nicotine concentration strengths presented as mg/ml (0-60 mg/ml) and percent nicotine (0-6%) from "no nicotine" to "very high nicotine." Participants also viewed pairs of nicotine concentrations (e.g., 18 mg/ml vs 5%) and indicated which concentration was stronger or if the concentrations were equivalent.


RESULTS
On average, participants correctly identified 5.92 (2.68) of 18 nicotine strengths, correctly identifying strengths labeled as mg/ml (3.47 [2.03]) more often than percent nicotine (2.45 [1.38], p< .001). Excluding nicotine-free, participants rated concentrations presented as mg/ml as stronger, more addictive, and more harmful than equivalent concentrations presented as percent nicotine. Participants seldom correctly identified that one concentration was stronger or that both were equivalent (7.58 [5.88] of 19 pairings), although they more often correctly identified the stronger concentration when it was presented in mg/ml (4.02 [SD = 3.01]) than in percent nicotine (2.53 [2.73]), p < .001). The most consistent predictor of correct answers on these tasks was familiarity with using both products labeled as mg/ml and labeled as percent nicotine.


CONCLUSIONS
Young e-cigarette users had difficulty understanding nicotine concentrations labeled using the most common metrics, raising concerns about inadvertent exposure to high nicotine levels and suggesting that a more intuitive labeling approach is needed.


IMPLICATIONS
This study extends prior work showing that young e-cigarette users often are uncertain whether the e-cigarettes/e-liquids they use contain nicotine by demonstrating that adolescents and young adults have difficulty understanding nicotine concentrations labeled using the two most common metrics (mg/ml and percent nicotine). Errors generally underestimated nicotine strength, and users were not able to accurately compare nicotine concentrations presented as mg/ml and percent nicotine. Difficulty understanding labeling metrics persisted even after accounting for user characteristics like age and vaping experience, suggesting that a novel, easy to understand labeling system is needed to convey information about nicotine strength accurately.