This is a two-arm, stratified cluster-randomized controlled pilot trial evaluating the feasibility and preliminary effectiveness of the World Health Organization's Self-Help Plus (SH+) intervention for stress reduction among social service workers employed by the Istanbul Provincial Directorate of Family and Social Services (ASHP). Four institutions (clusters) are randomized 1:1, stratified by service type, to receive either SH+ plus Enhanced Care as Usual (ECAU) or ECAU only, with a target of 50 participants (25 per arm). The primary aim is to assess feasibility indicators (recruitment, session attendance, retention, and acceptability) to inform a future full-scale definitive trial. Preliminary effects on perceived stress and related mental health and well-being outcomes are examined as secondary outcomes.

Social service workers are chronically exposed to traumatic content and occupational stress, placing them at elevated risk for psychological distress and secondary traumatic stress. A universal-prevention approach is adopted: no individual stress threshold is required for inclusion, as the occupational context itself serves as a high-risk filter.

Randomization is performed at the institution (cluster) level rather than the individual level to prevent contamination, accommodate the group format of the intervention, and reflect logistical realities of the institutions. Two clusters are allocated to the intervention arm and two to the control arm (1:1), stratified by service type. The allocation list is generated by a researcher independent of the field team, and assignment is revealed only after baseline (T0) assessment is complete. The trial is single-blind: participants and facilitators cannot be blinded, but outcome assessment is self-report via online forms (structural assessor masking) and the data analyst is blinded to group allocation (groups coded A/B until analysis is complete).

The SH+ intervention is a low-intensity, guided self-help program based on Acceptance and Commitment Therapy, delivered by trained non-specialist facilitators in a group format across five weekly sessions of approximately two hours each. It uses a pre-recorded audio course complemented by the illustrated self-help book "Doing What Matters in Times of Stress"; participants receive the book and weekly audio exercises for between-session practice. The ECAU control comprises continued access to existing institutional support and routine services plus a comprehensive psychoeducational information pack (stress-coping strategies, recognition of stress symptoms, and pathways to mental health and psychosocial support services in Istanbul). After the 3-month follow-up (T2), control-arm participants are offered the opportunity to attend SH+ sessions.

Assessments are collected at baseline (T0, pre-randomization), post-intervention (T1), and 3-month follow-up (T2) via self-report online forms. Feasibility progression thresholds are pre-specified: recruitment rate ≥70%, session attendance ≥70% (attending at least 3 of 5 sessions), and follow-up completion ≥75%. Preliminary effectiveness is analyzed using design-effect-adjusted methods or linear mixed models accounting for clustering; effect sizes (Cohen's d) with 95% confidence intervals are reported. The intraclass correlation coefficient (ICC) for the primary clinical outcome (PSS-10) is estimated to inform sample-size planning for a future full-scale cluster RCT.

Inclusion Criteria:

• Currently employed (permanent, contracted, or temporary staff) at an institution under the Istanbul Provincial Directorate of Family and Social Services
• Able to read and write in Turkish
• Willing to participate voluntarily
• Provides written informed consent

Exclusion Criteria:

• Imminent suicide risk, screened at baseline (T0) via PHQ-9 item 9; participants scoring 2 or higher are not enrolled and are immediately referred to a mental health professional
• Active psychosis, severe substance use disorder, or severe intellectual disability
• An acute medical condition that would preclude participation
• Planned extended leave (e.g., maternity or unpaid leave) during the study period

As this is a pilot feasibility trial, a data-sharing plan has not yet been finalized. Decisions regarding sharing of de-identified individual participant data will be made in line with KVKK (Turkish data protection law) requirements and institutional policy, and updated in this record accordingly.

Single-blind: outcome assessment is by self-report online forms and the data analyst is blinded to allocation. Participants and facilitators are not blinded