Mental health issues among older adults are an escalating global public health priority. Recent systematic reviews estimate that 15% to 20% of older adults experience major depressive disorder [1], while the global prevalence of depressive symptoms in this demographic reaches approximately 35% [2]. Early prevention and timely intervention are critical to reducing the impact of mental health conditions on individuals, reducing caregiver burden, and preventing the escalation of mild conditions into chronic psychiatric disorders or suicide [3-5]. Despite the availability of social services, older adults frequently delay or forgo professional help. This untreated duration often leads to exacerbated health outcomes and significantly higher longitudinal health care expenditures [6].

This underuse of mental health interventions is particularly pronounced among Chinese populations. Barriers include a strong cultural emphasis on self-reliance, reliance on informal or traditional resources, and a low perceived need for formal psychiatric help [7]. In high-density urban environments such as those in Hong Kong, despite a well-developed social service infrastructure, there remains a critical need for innovative strategies to bridge the gap between service availability and community uptake [8].

The theory of planned behavior (TPB) provides a robust framework for understanding the mechanisms underlying help-seeking, conceptualizing help-seeking as a complex, multistage process driven by attitudes, subjective norms, and perceived behavioral control [9,10]. In the context of mental health, this process is further complicated by social stigma, which is negatively correlated with help-seeking intentions among older adults with depression [11]. In older Chinese populations, cultural values such as “face-saving” and familial reliance significantly deter help-seeking [12-14]. Recognizing these nuances, a revised TPB model for Chinese contexts suggests that subjective norms (perceived social pressure and approval) serve as the primary antecedent influencing both attitudes and perceived behavioral control, ultimately driving intention [15]. Consequently, interventions targeting subjective norms may be the most effective means of achieving behavioral change.

“Nudging” alters choice architecture to steer individuals toward better decisions without restricting options [16]. Although it has been applied to geriatric health behaviors such as nutrition and vaccination [17], its application to mental health help-seeking remains nascent [18]. Existing interventions often rely on institutional-level gatekeeper training or psychoeducation [19,20]. However, daily, individual-level digital interventions offer a scalable alternative. For older Chinese adults, who are highly sensitive to social conformity, “social norm nudges” highlighting socially approved behaviors are hypothesized to be particularly effective [21,22]. Furthermore, incorporating visual cues (pictorial nudges) can improve attention, comprehension, and information recall, especially among populations with growing digital literacy [23-25]. To ensure cultural resonance, these nudges must be tailored through co-design with the target population.

This study aims to evaluate the effectiveness of descriptive norm nudges and pictorial norm nudges compared to an active control (mental health service information) in improving subjective norms and help-seeking intentions among older adults in Hong Kong. We hypothesize that both the descriptive norm nudges and the pictorial norm nudges groups will outperform the control group at postintervention assessment and at the 3-month follow-up.

Ethics approval was granted by The Hong Kong Polytechnic University Institutional Review Board (reference HSEARS 20231109001; approval date: Nov 10, 2023). Participants receive compensation for their participation at the baseline, after the intervention, and 3 months after intervention. Written informed consent is obtained from all participants. Consent has been obtained for the use of any image-based nudge materials in which identifiable individuals appear. Model consent forms are available on request. Participants may withdraw from the study at any time. Confidentiality will be maintained through the use of unique participant codes, and study records will be accessible only to authorized research personnel. Findings will be disseminated via academic conferences and peer-reviewed publications.

This is a 3-arm, parallel-group randomized controlled trial (RCT) with a 1:1:1 allocation ratio. Participants complete assessments at 3 time points: baseline (T0), immediately after intervention (T1), and 3 months after intervention (T2). This protocol is reported in accordance with the SPIRIT (Standard Protocol Items: Recommendations for Interventional Trials) 2025 guidelines [26] (Checklist 1).

The study is conducted in Hong Kong. Participants are recruited through the university research center website, social media, and community-based aged care services. The inclusion criteria are as follows: (1) aged ≥60 years, (2) able to read Chinese, and (3) ownership of a smartphone capable of receiving WhatsApp (Meta Platforms) texting (words and images). The exclusion criteria include the following: (1) a severe mental disorder, (2) cognitive impairment, (3) severe visual impairment, and (4) communication difficulties precluding informed consent.

All participants receive 1 brief message daily for 14 consecutive days, requiring less than 30 seconds to read. To encourage engagement, all participants are invited to provide brief responses (eg, emoji reactions or short replies) following each message. Participants will be discontinued from the intervention if they demonstrate sustained nonengagement, defined as failing to open or respond to study messages for 3 consecutive days. Participants may also withdraw voluntarily at any time without penalty.

Following the baseline assessment, a computer-generated sequence assigns participants to the pictorial norm nudge, descriptive norm nudge, or control groups in a 1:1:1 ratio. An independent staff member manages allocation concealment. Due to the visible nature of the intervention formats (pictorial messages, text-only messages, or informational content), participant blinding is limited. To minimize expectation and self-report bias, all groups receive interventions framed as mental health promotion messages, and identical assessment procedures are applied across groups. We use standardized and validated psychometric scales that do not directly reference the intervention materials. Although participant blinding is limited, the outcome assessors and the data analysis team will remain fully blinded to group allocation until all primary analyses are completed.

A flowchart of the procedure is shown in Figure 1, and the study timeline is presented in Table 2. First, eligible individuals provide written informed consent either online or in person during the recruitment phase. Following enrollment, participants complete the baseline assessment (T0), which captures demographic information and baseline outcome measures. Randomization occurs immediately after baseline assessment. Participants then enter the 14-day intervention phase, during which they receive automated daily messages based on their assigned study arm. Immediately following this 14-day period, the postintervention assessment (T1) is administered. Finally, a follow-up assessment (T2) is conducted 3 months after the intervention to evaluate the sustainability of intervention effects. Completion of assessments at each time point is acknowledged with small tokens of appreciation to encourage retention.

The study procedures pose a low risk to participants. Participants’ well-being is monitored remotely throughout the trial, with established referral protocols in place should any participant experience distress. Trial progress and safety are reviewed in biweekly meetings led by the principal investigator.

Twelve community-dwelling older adults co-designed the nudge content but were not involved in the trial’s implementation. A journal manuscript will be prepared to present the results after the trial is completed; participants and partner community centers will be acknowledged in the manuscript. A brief summary of the results in plain language will be provided to all participants and community partners.

This protocol describes an RCT evaluating co-designed norm-based nudges to promote mental health help-seeking intentions among older adults. We expect that modifying perceived subjective norms will directly improve help-seeking intentions, confirming the applicability of a culturally adapted TPB framework. Furthermore, by isolating textual and pictorial components, this study aims to clarify how visual communication formats influence the efficacy of digital nudges among older populations. If effective, the intervention will provide a scalable, low-cost mobile health (mHealth) strategy that can be readily integrated into community health promotion.

A primary strength of this study is its participatory co-design approach, ensuring the nudges are culturally resonant and tailored to the target population’s lived experiences. Second, the rigorous 3-arm design isolates specific behavioral mechanisms by systematically controlling for informational and visual elements. Finally, the use of daily microinterventions via WhatsApp creates a highly scalable, low-burden model suited for real-world implementation.

However, certain limitations must be acknowledged. Outcomes rely on self-reported intentions rather than objective help-seeking behaviors, such as actual clinic visits, which may inflate the observed intervention effects. Additionally, the requirement for smartphone ownership introduces potential selection bias toward more digitally literate older adults, thereby slightly reducing the generalizability of the findings. Finally, the 3-month follow-up limits conclusions regarding long-term behavioral maintenance.

If effective, this intervention may offer a scalable, low-resource strategy for promoting mental health help-seeking among older adults. Future research should extend this framework by examining objective service use metrics to determine whether intentions translate into actual behavior. Adapting the intervention for clinical populations or different cultural contexts will further validate the generalizability of norm-based nudging. Additionally, integrating these digital nudges directly into existing health care infrastructures or community services could be explored to facilitate immediate transitions from intention to actionable care.

This trial evaluates a novel, co-designed digital nudge intervention targeting mental health help-seeking among older Chinese adults. By combining behavioral theory, participatory design, and ubiquitous mobile messaging, this study will generate valuable evidence on how to leverage choice architecture and social norms to improve mental health care use among aging populations.