OBJECTIVE: We sought to systematically review the literature on electronic nicotine delivery systems (ENDS, also called electronic cigarettes) awareness, use, reactions and beliefs.
DATA SOURCES: We searched five databases for articles published between 2006 and 1 July 2013 that contained variations of the phrases 'electronic cigarette', 'e-cigarette' and 'electronic nicotine delivery'.
STUDY SELECTION: Of the 244 abstracts identified, we excluded articles not published in English, articles unrelated to ENDS, dissertation abstracts and articles without original data on prespecified outcomes.
DATA EXTRACTION: Two reviewers coded each article for ENDS awareness, use, reactions and beliefs.
DATA SYNTHESIS: 49 studies met inclusion criteria. ENDS awareness increased from 16% to 58% from 2009 to 2011, and use increased from 1% to 6%. The majority of users were current or former smokers. Many users found ENDS satisfying, and some engaged in dual use of ENDS and other tobacco. No longitudinal studies examined whether ENDS serve as 'gateways' to future tobacco use. Common reasons for using ENDS were quitting smoking and using a product that is healthier than cigarettes. Self-reported survey data and prospective trials suggest that ENDS might help cigarette smokers quit, but no randomised controlled trials with probability samples compared ENDS with other cessation tools. Some individuals used ENDS to avoid smoking restrictions.
CONCLUSIONS: ENDS use is expanding rapidly despite experts' concerns about safety, dual use and possible 'gateway' effects. More research is needed on effective public health messages, perceived health risks, validity of self-reports of smoking cessation and the use of different kinds of ENDS.