This study aimed to evaluate the effectiveness and adherence of a fully automated, unguided internet-based relaxation program designed to reduce stress and anxiety in Hungarian adults with English proficiency. Conducted through two randomized controlled trials, the program delivered evidence-based audio exercises (e.g., mindfulness, breathing, progressive muscle relaxation, and imagery techniques) via the web. The key research questions were whether this non-native English language program could reduce symptoms of anxiety, stress, and depression, and whether adherence could be improved through design modifications. The first trial tested the original 4-week version, while the second trial tested a 3-week modified version with adherence-enhancing features. Primary outcomes included changes in anxiety, depression, and stress. The study contributes to understanding the feasibility and potential of low-cost, language-accessible digital interventions for underserved populations in less structured, real-world settings.

Study 1 tested a four-week program called the "28-day Relaxation Challenge." It included seven short audio sessions per week (3-12 minutes), incorporating mindfulness, mantra meditation, progressive muscle relaxation, guided imagery, acceptance-based techniques, and imaginal exposure. Participants were instructed to complete one audio session daily. Weekly assessments were administered to track engagement and symptom change. The content was housed on a Google Drive folder, and access to new exercises was contingent on completing weekly questionnaires.

Based on findings from the first trial, Study 2 implemented several design enhancements aimed at improving adherence. The revised program reduced the duration from four to three weeks and repackaged the content into fewer but longer weekly modules (3-4 per week, 9-23 minutes each), integrating several techniques into each module. Delivery was upgraded to a streamlined website interface, incorporating videos with on-screen text, simplified navigation, and built-in reminders. Motivational and reinforcement emails, as well as reflective end-of-week questions, were introduced to foster intrinsic motivation and usability. The intervention remained fully automated and unguided.

Both trials used waitlist control groups and were conducted with a 1:1 allocation ratio. Participants were recruited through Hungarian psychoeducational social media platforms without geographic or financial restrictions. Outcome measures included the Depression Anxiety Stress Scales (DASS-21), State-Trait Anxiety Inventory (STAI), and Perceived Stress Scale (PSS), among others. Adherence was monitored via self-reported engagement and weekly check-ins.

Statistical analyses included both per-protocol and modified intention-to-treat (MITT) frameworks. The MITT sample included those who completed the first weekly assessment, serving as a proxy for program initiation.

This research contributes to the understanding of how design adjustments in unguided digital mental health programs influence engagement and outcomes in real-world populations, particularly among non-native English speakers accessing interventions in English. The study also offers practical insight into feasible low-cost solutions for stress and anxiety in underserved populations.

Inclusion criteria:

• being at least 18 years old
• having a self-reported at least medium level English proficiency
• Internet literacy (an an implicit eligibility criterion, as the whole procedure was done entirely online)

There was no exclusion criteria.

De-identified individual participant data (IPD) is available to researchers upon request.