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E-cigarettes: an evidence update <br /> <br />70 <br />These findings have an important implication. Above the necessary minimum level of <br />nicotine, nicotine concentrations in e-liquid and even the concentrations in vapour, if <br />measured by standard puffing schedules, are of limited relevance. For light smokers, <br />18mg/ml ‘mild’ e-liquid may be sufficient, but they may also prefer a stronger liquid and <br />take shorter and less frequent puffs. A heavy smoker who would be expected to prefer a <br />28mg/ml ‘strong’ liquid may in fact chose a ‘moderate’ strength if they favour long and <br />frequent puffs. <br /> <br />In real-life use, vapers have no way of knowing in advance what liquid strength and <br />product characteristics they will prefer. As with other consumer products of this type , <br />such as cigarettes, coffee and soft drinks, vapers have to try several EC models and <br />different e-liquids before settling on a preferred product that matches their preferences. <br /> <br />For practical purposes, general labelling of the strength of e-liquid, along the lines used <br />for indicating coffee strength, may provide sufficient information for consumers. The <br />current vapers’ preferences suggest as a rough rule of thumb that ‘mild’ equates to 16– <br />20mg/ml, ‘medium’ to 21–26mg/ml and ‘strong’ to 27–36mg/ml. <br /> <br />Translating these findings into regulatory recommendations, it would seem that <br />regulation to enforce standard nicotine delivery may not be needed because nicotine <br />delivery is influenced by a host of factors, including user puffing preferences, and <br />because consumer preferences differ. EC products will hopefully continue to evolve <br />guided by differential market success, with the result that more smokers find EC helpful <br />and switch to them. <br /> <br />Summary <br />Across the middle range of nicotine levels, nicotine delivery to vapour is determined <br />primarily by mechanical and electrical characteristics of EC products and by the <br />duration and frequency of puffs. General labelling of the strength of e-liquids, along the <br />lines used for indicating coffee strength (eg mild, medium and strong), is likely to <br />provide sufficient information for consumers. <br /> <br />Nicotine delivery to e-cigarette users <br />To assess nicotine intake from EC, a number of studies took blood samples from <br />smokers during and after vaping. Table 8 summarises data from 17 studies that <br />investigated nicotine delivery from EC in humans. The narrative description of the <br />studies and additional details concerning their find ings are presented in Appendix C. <br /> <br />The two key questions in this field are: <br />a) How much nicotine EC deliver compared to cigarettes, and <br />b) How fast EC deliver nicotine compared to cigarettes.