Most smokers want to quit and make attempts to do so, but the majority of these attempts fail largely because the powerful addictive qualities of nicotine and non-nicotine sensory and behavioural cues [1, 2]. For those willing to quit, combination of pharmacotherapy and intensive behavioural intervention for smoking cessation can support their quit attempts and can double or triple quit rates [3, 4]. However, outside the context of a rigorous clinical trial (where there tends to be intensive support), their efficacy rates are somewhat lower, not exceeding 10% [5, 6]. Several population-based studies evaluating the value of pharmacotherapy outside the context of clinical trials have also shown modest quit rates with antismoking medications [7–9]. Consequently, the need for novel and more efficient approaches to smoking cessation interventions is unquestionable.

Electronic cigarettes (e-Cigs) are an attractive long-term alternative source of nicotine to conventional cigarettes because of their many similarities with smoking [10, 11]. Moreover, users report buying them to reduce cigarette consumption, to relieve tobacco withdrawal symptoms, to quit, and to continue having a ‘smoking’ experience, but with reduced health risks [12, 13]. Two RCTs have recently reported disappointingly low quit rates with e-Cigs; 4–8.7% for the ECLAT study in Italy [14] and 4–7.3% for the ASCEND study in New Zealand [15]. A likely explanation for the poor results is to be attributed to the unsatisfactory quality of the products under investigation, essentially first-generation cig-alike devices consisting of small rechargeable batteries and disposable cartridges (Figure 1A). Their lithium battery allowed only a limited number of puffs and required frequent recharging. Reliability was questionable due to the high frequency of technical malfunctions. Moreover, both products were not very efficient at delivering nicotine [16]. Presumably, these products were not performing adequately as cigarette substitutes.

Second-generation devices (or personal vaporizers (PVs)) are equipped with higher-capacity lithium batteries, much efficient vaporizing systems and cartridges that can be refilled with liquid solutions mainly consisting of propylene glycol (PG), glycerol, distilled water, flavourings and nicotine (i.e. e-Liquid) (Figure 1B). These devices assent to a more fulfilling vaping experience with the choice of an extensive number of puffs and e-liquid aromas, and thicker vapor [12, 13]. Moreover, nicotine delivery to the bloodstream using second-generation devices is consistently superior compared to “cig-alikes” [17, 18].

Consequently, PV use may result in higher quit rates compared to “cig-alikes”. With this in mind, we designed a prospective proof-of-concept study to monitor possible modifications in daily cigarette consumption in smokers switching to second generation PVs focusing on smoking reduction and abstinence. We also monitored product use and adverse events and evaluated participants’ perception and acceptance of the product.

Efficacy and safety of second generation PVs in long-term smoking cessation and/or smoking reduction studies have never been investigated. Here, we show for the first time that use of a second generation PV substantially decreases cigarette consumption without causing significant side effects in smokers not intending to quit. Participants were enthusiastic about using these products, the majority (i.e. 76%) completing the study with an overall quit rate of 36%. A further 30% of the participants were able to sustain ≥50% cigarette by the end of the study.

These preliminary findings are of great significance in view of the fact that all smokers in the study were, by inclusion criteria, not interested in quitting. Moreover, though not directly comparable with standard smoking cessation and/or reduction studies because of its design, success rates in the present study are not only higher than those obtained with pharmaceutical products for the treatment of nicotine addiction [23, 24], but also greater than those of first generation “cig-alikes” [14, 22]. In particular, comparison of current results with those obtained in a similar prospective 6-month pilot study with first generation “cig-alikes” published a few years ago [22] shows improvement in quit rates with PVs (22.5% for “cig-alike” users vs 36% for PVs users).

An explanation for the large success rate may be attributed to the high level of satisfaction with the performance of second generation PVs as cigarette substitutes. The high-capacity lithium battery did not require frequent recharge, and the efficient vaporizing systems allowed an uninterrupted vaping experience with sufficient number of puffs through the whole day. Moreover, the reliability of the PVs under investigations was more than satisfactory with only a few reported technical malfunctions. Although not specifically measured in this study, nicotine absorption using second-generation devices has been shown to be consistently superior compared to “cig-alikes” [17, 18]. The high level of satisfaction with the product under investigation is substantiated by the notion that 30 out of the 38 who attended the last study visit were still using their PVs. This together with the high retention rate and elevated rating in likeability scores indicates that quality and attractiveness of the study product may be playing a vital role in attaining large success rates. Nonetheless, no correlations were observed between daily consumption of e-Liquid and success rates suggesting that multiple mechanisms are at play.

Throat/mouth irritation, and dry throat/mouth, headache and dry cough were frequently reported at the beginning of the study. These are likely to be secondary to exposure to PG mist generated by the PVs; exposure to PG mist may occur from smoke generators in discotheques, theatres, and aviation emergency training and is known to cause ocular, mouth, throat, upper airway irritation and cough [25, 26]. However, with the exception of headache (a highly unspecific symptom), the irritative symptoms – and particularly dry cough - appeared to wane spontaneously with time. Of note, typical withdrawal symptoms of smoking cessation were not reported during the course of the study. It is possible that the PVs under investigation by providing a coping mechanism for conditioned smoking cues could mitigate withdrawal symptoms associated with smoking reduction and smoking abstinence. Dizziness, nausea and palpitations may be due to nicotine overdosing, but these were not common and substantially declined with time. The substantial reduction in the frequency of dizziness and the lack of reported palpitation at later time points may be due to the improved familiarisation with the puffing technique and/or to individual adjustments/reductions in e-liquid consumption. In contrast from other ENDDs such some heat-and-burn platforms that can generate toxic levels of eCO [27], the products under investigation lead to substantial reduction in eCO levels, as expected in this vapour category [14, 22, 28]. Although larger and longer studies will be required for a full assessment of their adverse events, the present findings add to the current evidence that vaping is by far a less harmful alternative to tobacco smoking [29, 30].

There are some limitations in our study. Firstly, this was a small uncontrolled study, hence the results should be interpreted with caution. However, it would have been quite problematic to have a placebo arm in a study in which smokers were not interested in quitting. Secondly, 32.5% of the participants failed to attend their final follow-up visit, but this is not unexpected in a smoking cessation study and study outcome measures were computed by intention-to-treat analysis. Thirdly, because of its unusual design (smokers not willing to quit, PVs were used throughout the entire study period) this is not an ordinary cessation study and therefore direct comparison with other smoking cessation products cannot be made. Fourthly, assessment of withdrawal symptoms in our study was not rigorous and it is likely that was liable to recall bias. Therefore, the reported lack of withdrawal symptoms in the study participants should be considered with caution. Lastly, because only a single nicotine strength (i.e. 9 mg/mL) and a single aroma (i.e. tobacco flavour) were investigated in this study, it is possible that we failed to further maximize success rates. It is now known that unrestricted access to a wider selection in e-Liquid nicotine strength and flavour variability play a pivotal role in the attractiveness and success rates of these products [31, 32].

Complete tobacco cessation is the best outcome for smokers, but the powerful addictive qualities of nicotine and of the ritualistic behavior of smoking create a huge hurdle, even for those with a strong desire to quit. Tobacco harm reduction (THR), the substitution of low-risk nicotine products for cigarette smoking, is a realistic strategy for smokers who have difficulty quitting. E-cigarettes are the newest and most promising products for THR [33]. This approach has been recently exploited to reduce or reverse the burden of harm in smokers with mental health disorders and chronic airway disease [34, 35].

E-cigarette is an attractive long-term alternative and safer source of nicotine to conventional cigarette [11, 12]. Since their invention in 2003, there has been constant innovation and development of more efficient and appealing products. Here we show for the first time that second generation PVs can substantially decrease cigarette consumption without causing significant side effects in smokers not intending to quit. Moreover, overall participants’ perception and acceptance of these products was very good, in particular for those who quit or reduced smoking. Compared to our earlier work with first generation “cig-alikes” [14, 22], technical problems and difficulties in use familiarization with second generation PVs were negligible. Improved products reliability and attractiveness might have contributed to the very low number of study failures and lost to follow-up and high success rates thus confirming the notion that these products are attractive substitutes for conventional cigarettes. Although large and carefully conducted RCTs will be required to confirm these preliminary encouraging observations, the notion that second generation PVs can substantially decrease cigarette consumption in smokers not intending to quit should be taken into consideration by regulatory authorities seeking to adopt proportional measures for the vapour category [36].