This protocol describes a community-based cluster randomized controlled trial in Kamalgonj Upazila, Moulvibazar district, Bangladesh, evaluating a theory-driven intervention to improve blood pressure (BP) control among adults with hypertension. The intervention is grounded in the Health Belief Model (HBM) and structured using the PRECEDE-PROCEED framework to address behavioural and structural barriers such as poor medication adherence, high salt intake, physical inactivity, inadequate fruit intake, tobacco use, fragmented care and limited access to affordable medicines.

Formative mixed-methods research in the study communities showed high levels of uncontrolled hypertension despite treatment, frequent non-adherence, unhealthy diet and activity patterns, heavy smokeless tobacco use and reliance on informal providers. These findings informed the PRECEDE phases (social, epidemiological, behavioural/environmental, educational/ecological and administrative/policy assessments) and the selection of intervention targets.

Twelve clusters (villages or wards of about 3,000-5,000 residents) will be randomised 1:1 to intervention or control, with around 40 participants per cluster (≈480 in total). Adults are eligible if they are ≥18 years, have physician-diagnosed hypertension or BP ≥140/90 mmHg on two occasions, have lived in the cluster ≥6 months and can provide informed consent; exclusions include severe comorbidities requiring intensive care, severe cognitive impairment and pregnancy or planned pregnancy within 12 months. Randomisation is stratified by urban/rural status and performed by an independent statistician, with outcome assessors and data analysts blinded where feasible. The sample size was calculated to detect a 5-7 mmHg difference in mean systolic BP at 12 months with 80% power, assuming a standard deviation of 20 mmHg, intracluster correlation of 0.02-0.05 and up to 15% loss to follow-up.

The intervention consists of four components delivered over 12 months by trained community health workers. Group education includes four bi-weekly 45-60-minute sessions on understanding hypertension, benefits of BP control, practical medication-adherence strategies and lifestyle modification (salt reduction, physical activity, healthy eating and tobacco cessation), using interactive methods and local success stories to influence perceived threat, benefits, barriers, cues to action and self-efficacy. Individual counselling and motivational interviewing (two one-to-one sessions at weeks 4 and 8) identify personal barriers, set SMART goals and build confidence for daily self-management.

Enabling strategies include community BP monitoring corners equipped with automated devices, reminder calendars with tick-boxes, pictorial Bengali leaflets on low-salt recipes and exercise, wallet cards summarising key messages, and linkages to affordable generic antihypertensives and government essential drug programmes, including collaboration with local pharmacy sellers and village doctors where feasible. Reinforcing strategies involve inviting family members to at least one group session, monthly follow-up calls or home visits from months 3-12 to provide encouragement and problem-solving, facilitation of informal peer support or walking groups, and public recognition or certificates for participants who achieve BP control or sustained behaviour change. Control clusters receive usual care without structured HBM-based education or community follow-up, and will be offered a condensed version of the intervention after 12-month follow-up.

Data are collected at baseline, 6 months and 12 months. Primary outcomes are change in mean systolic BP from baseline to 12 months and the proportion of participants with controlled BP (systolic <140 mmHg and diastolic <90 mmHg) at 12 months. Secondary outcomes include change in mean diastolic BP, BP control at 6 months, HBM construct scores, medication adherence measured with the Bangladesh Medication Adherence Scale, lifestyle behaviours (salt intake, physical activity, fruit and vegetable consumption, tobacco use), knowledge of hypertension and health-service utilisation (clinic visits, BP monitoring frequency and source of BP checks). BP is measured by trained data collectors using validated automated oscillometric devices following WHO/ISH guidelines, with two seated readings averaged at each visit.

Process evaluation will assess fidelity, reach, dose, acceptability and contamination using attendance registers, facilitator checklists, supervision forms, questionnaires and qualitative interviews. Impact evaluation will examine changes in HBM constructs, adherence, behaviours, knowledge and service use at 6 and 12 months, while outcome

Hypertension is a leading modifiable risk factor for cardiovascular disease, stroke, chronic kidney disease, and premature mortality worldwide, with a particularly high burden in low- and middle-income countries where awareness, treatment, and control remain suboptimal. In Bangladesh, national surveys indicate that approximately one in four adults has hypertension and fewer than half of treated individuals achieve adequate blood pressure control, reflecting gaps in medication adherence, lifestyle behaviours, and continuity of care. Formative mixed-methods research in the study area documented a high prevalence of uncontrolled hypertension despite widespread treatment, low adherence to antihypertensive medications, high dietary salt intake, low fruit consumption, physical inactivity, prevalent tobacco use, and fragmented care pathways that rely heavily on informal providers.

The Health Belief Model is a widely used theoretical framework for understanding and modifying preventive and treatment behaviours and posits that action is influenced by perceived susceptibility, severity, benefits, barriers, cues to action, and self-efficacy. The PRECEDE-PROCEED model provides a comprehensive planning and evaluation framework that links social, epidemiological, behavioural, and environmental assessments to educational, organisational, and policy strategies. Building on detailed formative work in rural and peri-urban communities in northeastern Bangladesh, this trial applies the Health Belief Model within the PRECEDE-PROCEED framework to design and evaluate a multicomponent, community-based educational intervention targeting key determinants of poor hypertension control.

This is a parallel-group, community-based cluster randomized controlled trial conducted in Kamalgonj Upazila, Moulvibazar district, Bangladesh. Clusters are defined as villages or wards with a population of approximately 3,000-5,000 residents and clear geographic boundaries; twelve clusters (six intervention, six control) are selected from an administrative sampling frame in collaboration with local health authorities and randomly allocated (1:1) to intervention or usual-care control after baseline data collection, stratified by urban-rural status. Adults are eligible if they are aged 18 years or older, have physician-diagnosed hypertension or documented systolic blood pressure 140 mmHg or higher or diastolic blood pressure 90 mmHg or higher on at least two screening occasions, have resided in the cluster for at least six months with no intention to move during the study period, and are able to provide informed consent; individuals with severe cognitive impairment, serious comorbidities requiring intensive care, or current or planned pregnancy within 12 months are excluded. The planned sample size is approximately 480 participants (about 40 per cluster), providing 80 percent power to detect a between-group difference of 5-7 mmHg in mean systolic blood pressure at 12 months, assuming a standard deviation of 20 mmHg, an intracluster correlation coefficient in the range 0.02-0.05, and up to 15 percent loss to follow-up.

The intervention is delivered over 12 months by trained community health workers using four integrated components grounded in Health Belief Model constructs and informed by the PRECEDE assessment. First, group education consists of four biweekly sessions (45-60 minutes each) conducted in community venues such as non-governmental organisation offices and uses interactive lectures, visual aids, group discussions, and role plays to address understanding hypertension and its complications, benefits of blood pressure control, medication adherence and management of side effects, and lifestyle modification including salt reduction, physical activity, healthy diet, and tobacco cessation. Second, individual counselling and motivational interviewing involve two one-to-one sessions (approximately 20-30 minutes each, at weeks 4 and 8) in which community health workers identify personal barriers such as cost, fear of side effects, low family support, and competing priorities, negotiate specific, measurable, achievable, relevant and time-bound behaviour change goals, and support self-management planning. Third, enabling strategies include establishing community blood pressure monitoring points with validated automated devices, providing simple pictorial educational materials in Bengali, medication reminder calendars, and wallet cards, sending periodic mobile phone reminders where feasible, and facilitating linkages to affordable antihypertensive medicines through government essential drug programmes and local pharmacies. Fourth, reinforcing strategies engage family members in at least one group session, promote informal peer support such as walking groups, provide regular follow-up contacts including monthly calls or home visits during months 3-12, and offer recognition for participants who achieve or maintain blood pressure control or demonstrate sustained behaviour change to strengthen social norms supportive of healthy behaviours.

Control clusters receive usual care available through existing government and private health services without additional theory-based educational or community mobilisation activities. All participants in both arms undergo data collection at baseline (before randomization), 6 months, and 12 months, conducted by trained interviewers and outcome assessors who are blinded to allocation where feasible. Blood pressure is measured using standardized procedures with validated automated oscillometric devices, with participants seated for at least 5 minutes and two readings taken 1-2 minutes apart on the same arm and averaged. Interviewer-administered questionnaires capture socio-demographic characteristics, scores on Health Belief Model constructs using a validated 38-item scale, medication adherence using a nine-item Bangladesh Medication Adherence Scale, lifestyle behaviours including salt use, physical activity, fruit and vegetable intake and tobacco use, hypertension knowledge, and health service utilisation including frequency and source of blood pressure monitoring and clinic visits.

The primary outcomes are change in mean systolic blood pressure from baseline to 12 months and the proportion of participants with controlled blood pressure at 12 months, defined as systolic blood pressure less than 140 mmHg and diastolic blood pressure less than 90 mmHg. Secondary outcomes include change in mean diastolic blood pressure, blood pressure control at 6 months, changes in Health Belief Model construct scores, medication adherence categories, lifestyle behaviours, hypertension knowledge, quality of life assessed using a brief validated instrument, and exploratory incidence of hypertensive emergencies or cardiovascular events based on self-report and record review. Process evaluation assesses fidelity including delivery of planned sessions and adherence to curriculum, reach including the proportion of eligible individuals enrolled and attending sessions, dose including number of sessions and follow-up contacts received and frequency of use of community blood pressure monitoring points, acceptability from the perspective of participants, family members, and providers, and contamination including exposure of control participants to intervention components.

Data are entered using secure electronic databases with double data entry, routine quality checks, and restricted access. Analyses will follow a pre-specified statistical analysis plan, using appropriate methods for clustered data and intention-to-treat principles. Effect estimates for primary and secondary outcomes will adjust for clustering and relevant baseline covariates, and exploratory mediation analyses will examine whether changes in constructs such as perceived barriers, cues to action, and self-efficacy mediate intervention effects on adherence and blood pressure.

Ethical approval will be obtained from an institutional review board prior to initiation, and written informed consent or thumbprint with witness for non-literate participants will be required from all participants. Confidentiality will be protected through anonymised identifiers and secure data storage, and clear referral pathways will be established for participants with very high blood pressure readings or suspected complications. If shown to be effective, the intervention is designed to be integrated into existing community health worker programmes and non-communicable disease services in Bangladesh, using low-cost materials and existing infrastructure to support sustainability and scale-up in similar low-resource settings.

Inclusion Criteria:

• Are aged 18 years or older.
• Have physician-diagnosed hypertension or documented systolic BP ≥140 mmHg or diastolic BP ≥90 mmHg on at least two screening occasions.
• Have resided in the cluster for at least 6 months and plan to remain during the study period.
• Are able to provide informed consent.

Exclusion Criteria:

• Severe cognitive impairment, serious comorbidities requiring intensive care (such as advanced cancer or end-stage renal disease), and current pregnancy or intention to become pregnant within 12 months.

Individual participant data will not be shared outside the study team because of confidentiality constraints and limited data management resources.

Outcome assessors and data analysts are planned to be blinded to group allocation where feasible