Research Question: Can we treat tobacco dependence among individuals in South Asia with the most severe forms of mental illnesses, in order to prevent the onset and progression of tobacco-related multiple-long term conditions (MLTCs)?

Background: Tobacco dependence is a chronic relapsing condition and a precursor to several MLTCs. In people with severe mental illness (SMI), tobacco use exacerbates health inequalities and reduces life expectancy. Efforts for tobacco cessation are

critical in addressing MLTCs in SMI populations, particularly in low-resource settings like South Asia, which have a high burden of tobacco-related morbidity and mortality.

Aims and objectives: We have previously adapted a behavioural intervention for smoking cessation in people with SMI (SCIMITAR UK) for India and Pakistan. We will now:

1. Further adapt the intervention (to be called SCIMITAR-South Asia[SA]) for all forms of tobacco users (including smokeless tobacco) and for SMI populations in Bangladesh.

2. Design contextually tailored implementation strategies to deliver SCIMITAR-SA in mental health services in Bangladesh, India and Pakistan.

3. Test the feasibility, acceptability and clinical effectiveness of SCIMITAR-SA, delivered face-to-face or remotely to individuals with SMI in mental health settings

4. Establish the cost-effectiveness of SCIMITAR-SA, understand the economic and distributional health gains of tobacco cessation in SMI and estimate the costs of scaling-up of tobacco cessation services across mental health facilities

5. Systematically assess the contextual barriers and drivers to delivering SCIMITAR-SA in order to guide further adaptations and tailoring of implementation strategies.

We will also build capacity in tobacco cessation and applied research in mental and physical multimorbidity.

Methods and timelines: In year 1, we will review evaluations of existing behavioural interventions for tobacco cessation in South Asia, hold consensus workshops with experts for adapting intervention content and delivery, and produce the SCIMITAR-SA

intervention package, logic model and fidelity index. Stakeholder workshops will identify implementation strategies for SCIMITAR-SA.

In year 2, we will conduct a pilot trial of SCIMITAR-SA compared to brief advice (n=100, with three and six months follow-ups) in Bangladesh, India and Pakistan to evaluate recruitment and retention, primary outcome data, and the feasibility and acceptability of SCIMITAR-SA.

In years 3-4, we will conduct a fully powered trial of SCIMITAR-SA with an embedded process evaluation, recruiting and randomising 1450 participants in Bangladesh, India and Pakistan to SCIMITAR-SA or brief advice. We will assess tobacco

abstinence at three, six (primary outcome) and 12 months. Qualitative methods will explore barriers and drivers to implementation, and identify an evidence-informed list of strategies to strengthen and scale-up implementation. An economic

evaluation will identify the cost-effectiveness of SCIMITAR-SA and its distributional health impacts from a health systems perspective. Throughout the programme, we will build research and clinical capacity and pathways to impact.

Anticipated Impact and Dissemination: SCIMITAR -SA has promising prospects of clinical and cost-effectiveness; we will ensure its sustainability through clinical capacity building and identifying appropriate methods for its wider implementation in South Asia. Through stakeholder engagement, we will ensure knowledge translation into practice and policy. We will enhance capacity in South Asia for applied health research