Depression is already the leading psychological disability around the world, impairing daily life, well-being, and social functioning and leading to personal and social costs. Despite the effectiveness of Evidence-Based Psychological Practices (EBPP), a significant percentage of depressive individuals remain untreated, especially in Primary Care (PC) settings in Spain. There are numerous barriers that limit access to EBPPs, including high costs, professional training, and adherence problems. Information and Communication Technologies (ICTs) offer a cost-effective way to disseminate and scale EBPPs to address these barriers. The iCBT program Smiling is Fun has been demonstrated to be a cost-effective treatment for depression in various Randomized Control Trials. However, adherence and implementation problems in real-world settings need to be addressed. Implementation research can help evaluate these challenges by identifying facilitators and barriers to the implementation process in PC. In this regard, including human support has been pointed out as a possible key factor in addressing the population's mental health needs and promoting treatment adherence.

The current study aims to examine the effectiveness, adherence rates, and implementation process of Smiling is Fun to address depression in a PC setting considering the influence of telephone support vs no support.

The proposed research is a Hybrid Effectiveness-Implementation Type I study, with a two-armed randomized controlled design, which will test a clinical intervention for major depressive disorder while gathering information on its implementation in a real-world setting. The study will include adult patients with mild to moderate symptoms of depression. Participants will be randomly assigned to one of two groups: self-applied psychotherapy or self-applied psychotherapy with psychotherapeutic telephone support. The trial will recruit 110 patient participants, with a loss-to-follow-up rate of 30 %.

A study protocol for a hybrid effectiveness-implementation study is presented with the aim to assess the implementation of Smiling is Fun for the treatment of depression in PC. The study evaluates the influence of telephone support during a self-administered intervention compared to unguided self-administration. The main goal is to address the barriers and facilitators of the implementation process and to promote treatment adherence. Ultimately, the results of the study could help in the uptake of sustainable resources so that the population could gain better access to psychological interventions in mental health services.