This study aims to evaluate the implementation outcomes of a pilot randomized controlled trial and to assess the preliminary efficacy of Problem Management Plus (PM+) in reducing symptoms of depression and anxiety among users at a Primary Health Care center in Chile.

Two intervention groups will be compared: PM+ versus care as usual (CAU). The process will include an evaluation of the feasibility of the study procedures, as well as the acceptability and fidelity of the PM+ intervention.

In Chile, only 19% of the population with mental health conditions has access to primary care services, highlighting the urgent need to expand mental health care availability. Training more healthcare professionals to deliver low-intensity psychological interventions could be a valuable approach to addressing this disparity.

The World Health Organization's Problem Management Plus (PM+) is a low-intensity, transdiagnostic, peer-delivered intervention designed for implementation in resource-limited settings to address common mental health disorders. In this context, PM+ serves as an evidence-based strategy that can help reduce gaps in healthcare services, particularly regarding availability and accessibility.

This study aims to evaluate the implementation outcomes of a pilot randomized clinical trial, including feasibility, acceptability and fidelity and to assess the preliminary efficacy of PM+ in reducing mental health symptoms among users at a primary healthcare center in Chile.

The study design is a single-blind pilot randomized controlled trial with a 1:1 allocation ratio, assessing two intervention arms for participants with depressive and/or anxiety symptoms over five weeks.

The study population consists of adults of 18 years or above with mild to moderate depressive and/or anxiety symptoms, living in the selected study region and enrolled in the primary health care center chosen to conduct the trial.

Two groups will be compared. The treatment group will receive five sessions of PM+. The control group will receive care as usual (CAU), which includes the regular mental health services provided at the primary health care center selected for the study.

Implementation outcomes of PM+ will be assessed, focusing mainly on feasibility, acceptability and fidelity. Additionally, preliminary efficacy outcomes of depression, anxiety and self-identified problems will be evaluated.

Inclusion Criteria:

• Individuals over 18 years old.
• Diagnosed with or presenting depressive and/or anxiety symptoms (through screening).
• Residents of the selected study region.
• Part of the population enrolled and validated in the pilot primary health care facilities.

Exclusion Criteria:

• Suicidal risk requiring immediate or urgent referral to care services.
• Suffering from severe psychiatric disorders or substance use disorders.
• Being in situations of declared risk that require protection (e.g., domestic violence).
• Moderate or severe disability.
• Incapacitating medical illnesses.
• Receiving other mental health treatments that could lead to over-intervention.

Individual Participant Data (IPD) will only be shared when required by regulatory institutions. In order to protect privacy and ensure the confidentiality of information, all data shared with research staff members without direct access to the case file will identify participants solely by their enrollment number and will be transmitted using depersonalized forms, such as the CRF. In the case it becomes necessary to share IPD with regulatory institutions, such as ethics committees or governmental agencies, the depersonalized enrollment number will be used to maintain the confidentiality of personal information.

Personal information will only be shared with public health care services or as required under Chilean legislation.