Discussion
We found evidence that access to a 12-week text messaging intervention produced higher self-reported smoking abstinence in comparison to treatment as usual only. Effects on abstinence were observed immediately after the intervention period and persisted 3 months later. In addition, amongst those who continued to smoke, those with access to the intervention reported a lower number of cigarettes smoked weekly. This is the first time the effectiveness of a text messaging smoking cessation intervention has been evaluated amongst the general population in Sweden, and while the point estimates of effect sizes were found to be larger than those of international studies, they are still comparatively similar. For instance, one meta-analysis of text messaging interventions reported an overall OR of 1.37 (95% CI = 1.25–1.51) for smoking abstinence [Participants were long-time smokers (mean 25.3 years), with a history of multiple quit attempts (mean 7.2 attempts), yet the intervention was effective and showed no evidence of being less effective amongst those having smoked for longer. This is encouraging, as its important to both find ways of preventing individuals from becoming long time smokers and help those who have smoked for a long time to quit. All participants were referred to existing resources for smoking cessation, yet access to the intervention still improved abstinence rates. About a quarter of intervention group participants decided to stop the program prematurely. We did not require participants to give any reason for doing so (in accordance with ethical procedures); however, we may speculate that this was due to the program not suiting their needs, that they decided to abandon their quit attempt, or that they felt that they no longer needed support as they had successfully quit. On the other hand, more than three quarters of participants used the program to completion, seemingly finding it a helpful tool.