The purpose of this study is to evaluate the efficacy of a smartphone application in enhancing Acceptance and Commitment Therapy group treatment for smoking cessation. This study also aims to elucidate the processes through which the treatment promotes smoking cessation and for whom it is most effective.

Smoking is the single biggest preventable cause of death in Ireland and costs the exchequer approximately €1-2 billion per annum. Currently, 19.2% of Irish people aged 15 and over smoke. Given the magnitude of human suffering and economic cost associated with smoking, the systematic empirical development of cost-effective smoking cessation interventions is a major public health need. Combining a group-based treatment for smoking cessation with a theoretically-consistent smartphone application has the advantage of augmenting therapeutic content delivered in the clinic with on-the-spot assistance in the individual's natural environment. In accordance, this study will evaluate the efficacy of a smartphone application in enhancing Acceptance and Commitment Therapy group treatment for smoking cessation. This study will also elucidate the processes through which the treatment promotes smoking cessation. Identifying such mediators of change can inform the enhancement of subsequent interventions, enabling them to retain efficacious elements and disregard redundant elements. Furthermore, this study will identify the participant characteristics associated with differential response to the treatment. Clarifying such treatment moderators can facilitate practitioners in selecting optimal treatments for individual service users.

Participants will attend a baseline assessment on an individual basis prior to their smoking cessation attempt. During this session, participants will provide a breath sample and complete a series of self-report measures: Fagerström Test of Nicotine Dependence, Commitment to Quitting Scale, smoking-related variables (e.g., years smoking, previous quit attempts, etc.), Avoidance and Inflexibility Scale, Mental Health Continuum-Short Form, Valuing Questionnaire, Present Moment Awareness Subscale of the Philadelphia Mindfulness Scale, and the Cognitive Fusion Questionnaire. Participants will then be randomly allocated to the combined treatment, ACT group treatment or group based Behavioural Support Programme. A post-treatment assessment will be conducted to investigate changes in the variables measured at baseline. In addition, a six-month follow-up assessment will determine whether the effects of the treatments are sustained over an extended period of time.

Inclusion Criteria:

• Aged 18 years or older
• Interested in quitting smoking in the next 30 days
• Smoking 10 or more cigarettes per day for at least the past 12 months
• Daily access to a smartphone that is compatible with applications from iTunes (iPhone) or Google Play (Android)

Exclusion Criteria:

• Currently participating in another smoking cessation intervention
• Failure to the meet inclusion criteria