The Community Mental Health Education and Detection (CMED) tool was designed and validated for community health workers (CHWs) in South Africa to promote mental health education, detection and linkage to care for adults at risk of mental health conditions. This study evaluated CMED scale-up using implementation research to understand reach and adoption.Routinely collected CHW data from three scale-up community areas were analysed over six months. Using the Reach and Adoption components of the RE-AIM framework, data included the (i) number of CMED administrations; (ii) proportion of identified presumptive cases; and (iii) proportion of referred cases who received care. These data identified high-and low-adopting CHW teams. Observations and repeated group discussions explored factors influencing adoption. CHWs completed 2,135 CMED administrations. Seventeen percent screened positive and were referred for further assessment at PHC facilities; 62% of those referred presented for assessment, diagnosis, and management. Adoption varied across teams. Barriers included poor data systems and inconsistent supply of mental health services. Supportive leadership and supervision were strong facilitators of adoption. Policy uptake signalled maintenance. Findings suggest the CHW-delivered CMED tool is viable and useful for narrowing the treatment gap by strengthening demand for and access to mental health services.