The Health Action for Psychiatric Problems In Nigeria including Epilepsy and SubstanceS (HAPPINESS) intervention is a multicomponent, community-based, mobile technology-supported intervention that integrates mental health into primary health care centers in Nigeria using the World Health Organization’s Mental Health Gap Action Programme-Intervention Guide (mhGAP-IG). This study evaluates its implementation and patient-level clinical impact using a quasi-experimental design (single cohort with pre- and post-measures).

The HAPPINESS intervention implementation demonstrated high feasibility with 84% adoption rate (% of participating primary health centers that completed its roll out) and 81% fidelity (% of clinicians who completed required intervention components according to the protocol). Retention rate in care at 12 months was 86%. Among patients with complete clinical records analyzed (n = 178), there was a statistically significant reduction in 9-item Patient Health Questionnaire scores from baseline (Md = 9.5) to 6 months (Md = 3.0) post-intervention (z = 80.5, p < 0.001), with a large effect size (r = 0.8) and statistically significant reduction in Brief Psychiatric Rating Scale scores from baseline (Md = 36.0) to 6 months (Md = 17.0) post-intervention (z = 128.5, p < 0.001), with a large effect size (r = 0.9).

Mobile technology-enhanced, mhGAP-IG-based efforts to scale-up mental health services in Nigeria are feasible and effective.