New-generation EC devices were more efficient in nicotine delivery, but still delivered nicotine much slower compared to
tobacco cigarettes. The use of 18 mg/ml nicotine-concentration liquid probably compromises ECs' effectiveness as smoking substitutes;
this study supports the need for higher levels of nicotine-containing liquids (approximately 50 mg/ml) in order to deliver nicotine more effectively and
approach the nicotine-delivery profile of tobacco cigarettes.