Abstract: This review includes 19 studies with a total of 14,890 participants. We categorised the included studies according to the modes used to deliver the recruitment strategy: head to head comparison of individual recruitment strategies; comparison of the same delivery mode but with different content or intensity; and the addition of another mode to an existing recruitment method. We identified three studies that made head-to-head comparisons of different types of recruitment strategies. Of these, only one study detected a significant effect, finding that a personal phone call was more effective than a generic invitation letter (RR 40.73, 95% CI 2.53 to 654.74). Five studies compared interventions using the same delivery modes but different content. Results showed that tailored messages through an interactive voice response system resulted in a higher recruitment rate than assessment of smoking status alone using the same system (RR 8.64, 95% CI 4.41 to 16.93), and that text messages indicating scarcity of places available were more effective than generic text message reminders (RR 1.45, 95% CI 1.07 to 1.96). One study compared interventions using the same delivery mode but different intensity and found that allowing for more phone call attempts to reach potential participants can result in better recruitment (RR 1.87, 95% CI 1.61 to 2.18). Finally, 10 studies investigated the effect of adding a recruitment mode to existing recruitment strategies. Findings showed that: adding a text message reminder or real quotes from participants to a personal phone call improved recruitment of participants (RR 3.38, 95% CI 1.26 to 9.08 and RR 29.07, 95% CI 1.74 to 485.70, respectively); that adding a personal phone call to an existing newsletter can also increase recruitment rates (RR 65.12, 95% CI 4.06 to 1045.4]); that a reactive-proactive recruitment phase is more effective than a proactive phase alone (63.8% versus 47.5%, RR not available); and that active recruitment at schools is more effective than passive recruitment (p < 0.001, denominator not available for calculation of RR). Additionally, a number of studies in this category showed that providing incentives can effectively increase the number of participants recruited into smoking cessation programmes. Out of the 19 included studies, only four reported on the effect of recruitment strategy on smoking cessation at six months or longer. Three of these studies compared strategies that used the same delivery mode with different content. Their results were non-significant. The remaining three studies evaluated adding an additional mode to an existing recruitment intervention. Only one of them showed a significant difference in the levels of smoking cessation that favoured the enhanced recruitment strategy, but this may have reflected the offer of incentives once in the programme rather than the recruitment strategy itself (RR at 15 or 18 months 2.60, 95% CI 1.48 to 4.56). The substantial heterogeneity across the included studies restricts our ability to draw firm conclusions about the effectiveness of different recruitment strategies in relation to recruitment of participants into smoking cessation programmes or levels of smoking cessation. The limited evidence, however, suggests that the following elements may improve the recruitment of smokers into cessation programmes: personal, tailored interventions; recruitment methods that are proactive in nature; and more intensive recruitment strategies (i.e., those strategies that require increased contact with potential participants).

Plain-language summary: This review aims to identify whether certain recruitment strategies can help to increase the number of smokers enrolling into quit services. It also aims to determine whether these recruitment strategies have any impact on people successfully quitting smoking at six months or longer. This review covers 19 studies, with almost 15,000 participants, but the significant differences across these studies meant that we were unable to draw conclusive answers to our research questions. Our findings do, however, suggest that the following elements could result more people joining quit smoking programmes: (1) recruitment strategies tailored to the individual; (2) proactive strategies; and (3) increased contact time with potential participants. This review also highlights the areas within this field that need more attention: identifying the elements of a recruitment strategy that are more likely to effectively engage smokers; whether or not elements of recruitment strategies have an impact on quit rates; and identifying those recruitment strategies (or different combinations of particular recruitment strategies with certain smoking cessation programmes) that work better for different population groups.