Evaluating the Efficacy of a Guided and Unguided Internet-Based Self-help Intervention for Chronic Loneliness: Protocol for a 3-Arm Randomized Controlled Trial

Background: Loneliness, or perceived social isolation, is prevalent in both the general population and clinical practice. Although loneliness has repeatedly been associated with mental and physical health, research on interventions that reduce loneliness effectively is still rather scarce. Objective: This study aims to evaluate the efficacy of a guided and an unguided version of the same internet-based cognitive behavioral self-help program for loneliness (SOLUS-D) for adults. Methods: A total of 250 participants will be randomly assigned to 1 of 2 intervention groups (SOLUS-D with guidance or SOLUS-D without guidance) or a wait-list control group (2:2:1 allocation ratio). Adult participants experiencing high levels of loneliness will be recruited from the general population. Individuals currently experiencing at least moderately severe depressive symptoms, an ongoing severe substance use disorder, previous or current bipolar or psychotic disorder, or acute suicidality will be excluded from the trial. Assessments will take place at baseline, 5 weeks (midassessment), and 10 weeks (postassessment). The primary outcome is loneliness assessed using the 9-item University of California, Los Angeles Loneliness Scale at the posttreatment time point. Secondary outcomes include depressive symptoms, symptoms of social anxiety, satisfaction with life, social network size, and variables assessing cognitive bias and social behavior. The maintenance of potentially achieved gains will be assessed and compared at 6 and 12 months after randomization in the 2 active conditions. Potential moderators and mediators will be tested exploratorily. Data will be analyzed on an intention-to-treat basis. Results: Recruitment and data collection started in May 2021 and are expected to be completed by 2022, with the 12-month follow-up to be completed by 2023. As of the time of submission of the manuscript, 134 participants were randomized. Conclusions: This 3-arm randomized controlled trial will add to the existing research on the efficacy of loneliness interventions. Furthermore, it will shed light on the role of human guidance in internet-based treatments for individuals with increased levels of loneliness and the possible mechanisms of change. If SOLUS-D proves effective, it could provide a low-threshold, cost-efficient method of helping and supporting individuals with increased levels of loneliness.