The costs, outcomes and returns on investment of a package of intersectoral interventions for mental, neurological, and substance-use disorders, and intellectual disabilities in South Africa

South Africa faces a significant burden from mental, neurological, and substance-use (MNS) conditions, with a substantial treatment gap that hampers the country's progress toward universal health coverage (UHC). Despite National Health Insurance (NHI) reforms, equity in access, affordability and preparedness remain concerns. The South African Mental Health Investment Case (MHIC) was commissioned to evaluate the costs and benefits of implementing mental health interventions over a 15-year period to inform national planning and budgeting. The analysis incorporated a comprehensive stakeholder consultation process including a Delphi study for expert consensus and uses the WHO Inter-UN OneHealth Tool and Excel-based modelling to estimate health and economic benefits. The MHIC estimates substantial economic and social returns, particularly for interventions targeting common mental health conditions, with benefit to cost ratios of 4.0 and 3.6 to 1 for adult and childhood depression, 4.7 to 1 for perinatal depression and 1.5 and 0.6 to 1 for adult and childhood anxiety, respectively. The total investment needed represents approximately 11.6% of the current health budget and aligns with recommended international norms for mental health funding. The cost of inaction is significant, unaddressed MNS conditions could cost South Africa 4% of its GDP annually. The MHIC highlights the value of early prevention programs, including school-based interventions and targeted psychosocial support, which could avert prevalent cases and enhance productivity. By reallocating resources towards primary and community-based care, the MHIC advocates for an efficient and sustainable approach aligned with South Africa’s UHC goals, emphasizing the critical need for intersectoral collaboration. • Mental health scale up represents 11.6% of the current health budget. • Unmet mental health needs consume 4% of the country’s GDP annually. • Cost of inaction on mental health far exceeds the investment required for scale-up. • Doubling investments increases coverage 4.4-fold due to community care efficiencies. • Scaling mental health care yields high returns across multiple conditions.