Major depressive disorder (MDD) is a mental disorder that can have a persistent impact on both affected individuals and their family members [1]. Specifically, family caregivers often experience psychological distress and daily burdens while providing emotional support, assisting with daily activities, and managing crises [2,3].

Among these caregivers, young adults represent a particularly overlooked population [4,5]. Young adulthood is a developmental period characterized by major life transitions, such as achieving vocational independence, forming partnerships, and beginning parenthood. Therefore, assuming caregiving responsibilities for a family member with MDD during this stage may impose unique burdens distinct from those experienced in other life stages [6,7]. Furthermore, these responsibilities often conflict with developmental tasks and everyday obligations, potentially hindering access to support and help-seeking services. Accordingly, young adult caregivers of a family member with MDD are considered to have distinct support needs [8]. A recent meta-analysis of randomized controlled trials (RCTs) found that young people with a parent affected by serious physical or mental illness are at increased risk of psychological and developmental difficulties, and that psychosocial interventions have small but significant benefits for psychological outcomes and positive adjustment. However, young adults remain underrepresented in this evidence base, with only one trial specifically targeting young adults [9].

Family psychoeducation (FPE) has been recognized as a promising intervention for caregivers of a family member with MDD. Previous studies have suggested that FPE may reduce psychological burden and distress among family caregivers [10,11]. However, existing research has primarily focused on middle-aged and older spouses or parents, and intervention studies specifically targeting young adult caregivers remain limited [11,12]. Consequently, it remains unclear whether existing evidence regarding FPE can be generalized to young adult caregivers.

Furthermore, supporting young adult caregivers requires both intervention content and delivery modes that are compatible with work, study, parenting, and other responsibilities. In this regard, online support is a particularly suitable approach for young adult caregivers balancing multiple roles because it mitigates time-related and geographic barriers [13,14]. However, one-way online support focused solely on self-help or information provision may not sufficiently address an individual’s life circumstances and psychological needs. Accordingly, recent studies have highlighted the importance of interactive online support that incorporates responsive communication tailored to users’ situations and opportunities for interaction with support providers [15,16].

From this perspective, videoconference-based family psychoeducation (vFPE) is a promising approach for providing interactive online support to young adult caregivers. Videoconferencing allows real-time interaction with a supporter and may facilitate flexible responses tailored to individual family circumstances and life contexts [17,18]. Additionally, an individualized, rather than a group, format was selected to reduce potential concerns about confidentiality and discomfort associated with group participation [19].

We previously developed vFPE for young adult caregivers and evaluated it in an unpublished preliminary single-arm study involving 12 participants. The findings provided preliminary evidence of the feasibility, acceptability, and safety of vFPE. However, challenges specific to RCTs, such as randomization acceptance and retention at 1-month follow-up assessments, remain unexplored. Therefore, before proceeding to a definitive RCT, it is necessary to evaluate the feasibility of conducting a waitlist-controlled RCT of vFPE for young adult caregivers.

This study aims to evaluate the feasibility of conducting a waitlist-controlled RCT of vFPE and the acceptability of the intervention among young adult caregivers of a family member with MDD. Specifically, it will assess recruitment, randomization, intervention completion, dropout rates, safety, and intervention acceptability to generate the foundational evidence to inform the design of a future definitive RCT.

This study is a waitlist-controlled pilot RCT designed to examine the feasibility of conducting a trial of vFPE for young adult caregivers of a family member with MDD. The primary objective is to evaluate the feasibility of the trial procedures, including recruitment, randomization, intervention delivery, and a 1-month follow-up assessment, as well as the acceptability of the vFPE intervention. These evaluations will provide foundational data for a future definitive RCT. The secondary objective is to explore preliminary changes in clinical outcomes, particularly anxiety and depressive symptoms. This protocol follows the SPIRIT (Standard Protocol Items: Recommendations for Interventional Trials) 2025 guidelines (Checklist 1) [20].

The eligibility criteria are as follows: (1) being aged 18 to 39 years, (2) having a spouse or a relative within the third degree of kinship who, according to participant-reported information, has been diagnosed with MDD by a physician, (3) providing care for that family member, and (4) being able to participate in the videoconference-based intervention using an internet connection and a computer or similar device.

In this study, the age range for young adult caregivers is broadly defined as 18 to 39 years. While the definitions of young adult caregivers vary across studies, this range was selected to encompass the Japanese life stages in which developmental tasks such as employment, career development, partnership, and parenting often overlap with family caregiving, reflecting the prolonged transition to adulthood [21]. This definition is also consistent with Japanese youth-support policies, in which people younger than 40 years may be included depending on the specific policy [22]. In addition, recent local government surveys of young carers in Japan have used 18 to 39 years as the target age range and reported that 4.8% to 6.8% of respondents were currently providing care for a family member [23,24]. Therefore, this study adopts the age range of 18 to 39 years to capture young adult caregivers with potential caregiving-related support needs. Participants will be spouses or relatives within the third degree of kinship to the family member with MDD, including siblings, children, and other relatives. The caregiver’s relationship to the family member with MDD will be recorded and summarized descriptively. In this study, “care” is not limited to physical assistance but broadly includes emotional support, assistance with daily living, and responses to psychological crises [25,26]. Therefore, eligibility will not be determined using rigid metrics for the specific types or duration of care; rather, the emphasis will be placed on whether individuals perceive themselves as having an ongoing supportive role.

The diagnosis and clinical background of the family member with MDD will be based on participant-reported information and will not be independently verified through direct clinical interviews, inquiries to physicians, or review of medical records to protect the family member’s privacy, reduce participant burden, and maintain the feasibility of recruitment in this pilot trial. To determine eligibility and reduce diagnostic uncertainty, the following information will be collected during eligibility screening based on information reported by the participant: (1) whether the family member has been diagnosed with MDD by a physician, (2) whether the participant has been directly informed of the diagnosis, (3) the time of diagnosis, (4) the duration of illness, (5) current psychiatric or mental health treatment status and frequency of visits, (6) history of past hospitalization, (7) major depressive symptoms currently experienced by the family member, and (8) any other known psychiatric diagnoses.

The exclusion criteria are as follows: (1) the participant is currently receiving outpatient treatment for a mental disorder, (2) the participant has a serious, progressive physical illness likely to hinder continued participation, or (3) the principal investigator determines that participation is difficult because of safety concerns, difficulty in understanding the study procedures, or substantial difficulty in maintaining participation. The first exclusion criterion was established because this pilot trial focuses on evaluating the feasibility of the trial procedures and the acceptability of vFPE under stable study conditions. Similar eligibility restrictions have been used in previous FPE trials for caregivers of people with mental illness [27]. Participants currently receiving outpatient treatment for a mental disorder may require individualized medical care or support beyond the scope of this study. Therefore, this criterion was intended to prioritize participant safety and reduce the potential influence of ongoing mental health treatment on the study findings.

Participants will be recruited from January 2026 to December 2027 through administrative agencies, family associations, and online platforms. Recruitment will continue until the target sample size of 24 participants is reached or until December 2027, whichever occurs first. The number of participants at each stage of recruitment, reasons for ineligibility or nonparticipation, and recruitment sources will be recorded and summarized descriptively.

Interested individuals will be asked to contact the principal investigator directly using the method outlined in the study information materials. Those who contact the investigator will receive a comprehensive explanation of the study, covering its purpose, procedures, and ethical considerations via videoconferencing. Subsequently, written informed consent will be obtained.

After providing written informed consent, potential participants will provide the background and clinical information required for eligibility screening via an online self-administered questionnaire. The principal investigator will assess eligibility based on the predefined inclusion and exclusion criteria. Individuals determined to be eligible will then complete the baseline outcome questionnaires online and be enrolled in the study. The planned participant flow through the trial is illustrated in Figure 1.

All exploratory outcomes will be assessed at 3 time points—baseline, postintervention, and 1-month follow-up—via self-administered questionnaires.

As this study is a pilot trial conducted prior to a future definitive RCT, the sample size was not determined via a formal power calculation. Instead, the target sample size was set at 12 participants per group (N=24).

This aligns with a commonly cited rule of thumb suggesting that approximately 12 participants per group may be appropriate for pilot studies [63]. This sample size may also provide preliminary data to inform the planning of a future definitive RCT [64].

If 9 out of 12 intervention-group participants complete the intervention, the completion rate will be 75.0% (95% CI 46.8%‐91.1%). If 17 of 24 participants complete the 1-month follow-up, the retention rate will be 70.8% (95% CI 50.8%‐85.1%). Recruiting 24 participants over 24 months would correspond to 1.0 participant per month (95% CI 0.64‐1.49). Because the CIs for completion and retention cross the prespecified 70% thresholds, these thresholds will guide rather than determine progression decisions. Despite the limited precision, these estimates can identify major feasibility problems and inform a future definitive RCT.

Upon eligibility confirmation and completion of the baseline assessment, participants will be randomly assigned in a 1:1 ratio to either the intervention or the waitlist control group. Randomization will be performed via UMIN INDICE Cloud (University Hospital Medical Information Network Center, The University of Tokyo Hospital), using the minimization method. Allocation factors include sex and age (<25 y vs ≥25 y). The 25-year age cutoff was selected based on prior literature regarding emerging adulthood and young adult caregivers. Age was selected as an allocation factor to balance the distribution of participants in earlier and later stages of young adulthood across groups [3,65].

The principal investigator will provide the study explanation and obtain written informed consent. A researcher independent of intervention delivery, outcome assessment, and statistical analysis will then register participants whose eligibility has been confirmed by the principal investigator and who have completed the baseline assessment. Following registration, the same researcher will perform centralized allocation via the UMIN INDICE Cloud. As the system generates group assignments only after participant registration, the group assignment will remain unknown to the intervention provider until allocation is completed. The allocation result will then be communicated only to the personnel necessary for intervention scheduling and delivery. Owing to the nature of the intervention, neither participants nor the intervention provider will be blinded.

Outcome data will be collected at 3 time points: baseline, postintervention, and 1-month follow-up, via online self-administered questionnaires. The schedule of enrollment, intervention, and assessments, including the timing of each outcome measure, is presented in Table 2. To maintain separation between intervention delivery and data management, data collection and management will be handled by a data manager independent of the intervention team. All collected data will be deidentified before storage and management.

To maximize retention and completion of 1-month follow-up assessments, participants will receive reminder emails or messages before each relevant intervention session and assessment time point. Furthermore, when necessary, flexible scheduling will be offered to accommodate participants’ needs and facilitate participation in the intervention sessions.

The reporting of study results will follow the CONSORT (Consolidated Standards of Reporting Trials) extension for randomized pilot and feasibility trials [66]. Exploratory outcomes will be analyzed according to randomized group allocation using available outcome data at each follow-up time point. Participant characteristics will be summarized using means and SDs for continuous variables and frequencies and percentages for categorical variables.

The primary outcomes, feasibility and acceptability, will be summarized descriptively. Recruitment pace will be reported as participants per month, while screening-to-randomization, intervention completion, and dropout rates will be reported as proportions with 95% CIs. Safety will be summarized descriptively based on the occurrence and characteristics of adverse events and serious adverse events. Acceptability will be summarized descriptively using CSQ-8-J scores among intervention-group participants with available postintervention CSQ-8-J data. Scores will be categorized as poor (8-13), fair (14-19), good (20-25), and excellent (26-32) [67].

Exploratory outcomes will be analyzed to obtain preliminary estimates of between-group differences and variability, rather than for formal hypothesis testing. Descriptive within-group changes, between-group differences in change scores, and 95% CIs will be presented. For HADS-T, the main exploratory comparison will be the between-group difference at postintervention. The between-group difference at the 1-month follow-up will be examined as a supplementary exploratory comparison.

Between-group differences at each follow-up time point will be estimated using a baseline-adjusted ANCOVA model. The dependent variable will be the HADS-T score at each follow-up time point. The model will include group as the independent variable, with baseline HADS-T, sex, and age category included as covariates. Sex and age category will be included as covariates because they are used in the minimization procedure [68].

Other exploratory outcomes will be analyzed using the same model structure, with the baseline score for each respective outcome, sex, and age category included as covariates. We will report adjusted mean differences, 95% CIs, and standardized effect sizes corrected for small-sample bias using Hedges g. Each follow-up analysis will include participants with available outcome data at that time point. Missing data will be summarized by group and time point, and no imputation of missing outcome data will be performed. No adjustment for multiplicity will be applied because all analyses of exploratory outcomes are intended to be preliminary. Statistical analyses will be performed using R software (R Foundation for Statistical Computing).

As this is a pilot trial not intended to provide a definitive test of effectiveness, all inferential results will be interpreted as exploratory. The main purpose of the clinical outcome analyses is to obtain preliminary estimates of outcome variability to inform the design of a future definitive RCT. Due to the small sample size, no subgroup or sensitivity analyses will be performed in this pilot trial.

As this is a minimal-risk pilot trial, an independent data monitoring committee will not be established, and external auditing will not be conducted. Instead, study progress and safety will be monitored by the principal investigator and coinvestigators through the regular review of recruitment, retention, intervention delivery, adverse events, and data collection. No formal interim analyses are planned because of the small sample size and pilot nature of the trial. There are no prespecified statistical stopping guidelines. However, if serious safety concerns arise, the principal investigator, in consultation with the coinvestigators and the ethics committee as needed, will determine whether the trial should be modified or terminated.

Adverse events will be monitored during intervention sessions and at the postintervention and 1-month follow-up assessments. Assessment items will include increased psychological distress, worsening depressive or anxiety symptoms, heightened study-related burden, and other mental or physical problems.

If marked deterioration is observed, the research team will determine the appropriateness of continued participation and, if necessary, discontinue the intervention or withdraw the participant from the study. In such instances, participants will also be encouraged to seek appropriate medical care or support services. All adverse events will be recorded, and any serious adverse events will be promptly reported to the ethics committee.

This study will be conducted with the approval of the Research Ethics Committee, Faculty of Nursing, Toho University (approval number RE2025016). The trial was registered in the Japan Registry of Clinical Trials (jRCT; trial ID jRCT1032250574) on December 17, 2025, prior to the commencement of participant enrollment.

Individuals interested in participating will receive a comprehensive written and verbal study explanation via videoconferencing. Written informed consent will be obtained by the principal investigator before the initiation of any study procedures. As all participants are adults aged 18 years or older, parental consent will not be required. Participants will be informed that their participation is voluntary and that they may withdraw from the study at any time without penalty. Signed consent forms will be stored securely, separately from the study data, in either a locked cabinet or a password-protected electronic environment accessible only to authorized research personnel.

Participants who complete all assessments will receive a QUO card worth JP¥ 5000 (approximately US $33) as compensation for their time and efforts. Any significant protocol modifications will be reviewed by the research team and submitted to the Research Ethics Committee, Faculty of Nursing, Toho University for approval prior to implementation. Trial registration details in the Japan Registry of Clinical Trials will also be updated accordingly. If necessary, participants will be informed of the changes, and additional consent will be obtained.

This pilot trial will evaluate the feasibility of conducting a waitlist-controlled RCT of vFPE for young adult caregivers of a family member with MDD. Although young adult caregivers often have substantial support needs, they remain an underserved population because they must balance caregiving with other developmental and social responsibilities, including employment, education, partnership, and parenting.

This study has 2 potential strengths. First, it will contribute to the limited evidence on supportive interventions for young adult caregivers of a family member with MDD, a population that has received relatively little attention despite their distinct developmental and psychosocial challenges. Second, it will examine the feasibility of conducting a waitlist-controlled RCT of vFPE and the acceptability of this brief videoconference-based intervention specifically designed to mitigate the time-related and geographic barriers to accessing support prevalent in this population.

These findings are expected to inform the design of a future definitive RCT. Recruitment indicators and sources will be used to refine strategies for future trials. Data on dropout, intervention completion, and acceptability will inform potential modifications to the intervention content and intervention delivery procedures. Estimates of outcome variability and findings from exploratory outcomes will inform the design of a future trial.

This study also has several limitations. First, as this is a small pilot trial, it is not designed to provide a definitive evaluation of intervention effectiveness; therefore, findings related to clinical outcomes should be interpreted as exploratory, and generalizability is limited. Second, all exploratory clinical outcome measures are based on participant self-report, and participant blinding is not feasible; therefore, the possibility of expectancy bias cannot be excluded. Third, data regarding the diagnosis and clinical history of the family member with MDD will be based solely on participant-reported information and will not be verified using medical records. Although caregiver-reported diagnostic information has been used in previous intervention studies involving caregivers of individuals with depression [14,69], relying on participant-reported information to identify psychiatric diagnoses may reduce diagnostic accuracy [70]. Diagnostic uncertainty or misclassification may remain if the diagnosis has changed over time or if comorbid psychiatric conditions are present. Fourth, excluding participants currently receiving outpatient treatment for a mental disorder may limit the generalizability of the findings to young adult caregivers receiving mental health treatment. This limitation is important because previous research has found that more than half of caregivers of patients with depressive disorder had a psychiatric diagnosis [49]. Therefore, caregivers with substantial mental health support needs may be underrepresented in this study. Finally, the requirement of internet access and the ability to complete online procedures may introduce selection bias, favoring individuals who have greater digital access or literacy.

This pilot trial will clarify the feasibility of conducting an RCT of vFPE for young adult caregivers of a family member with MDD. The findings are expected to provide preliminary evidence to inform the design of a future definitive RCT and advance the development of accessible support for this underserved population.