Background: Problematic social media use has been linked to reduced well-being and impulse control difficulties. While digital self-control apps show potential for reducing general app usage, they often lack customization, leading to limited effectiveness and increased user resistance. Their impact on problematic social media use remains uncertain. Objective: This study evaluates the effectiveness of the Wellspent app, a customizable mobile intervention app designed to promote self-regulated social media use by targeting user-defined problematic app use and offering tailored behavioral nudges. Methods: In a 3-week randomized controlled trial, 70 iPhone users (mean age 26.2, SD 5.6 years; 47/70, 67% female), regularly using at least 1 social media app, were randomly assigned to an intervention (n=35) or control group (n=35). The intervention group received personalized full-screen reminders with the option to quit or continue social media app use whenever an app session exceeded a self-defined time limit. Participants completed weekly online surveys measuring problematic social media use, problematic smartphone use, self-efficacy, and daily screen time on their most problematic app. Linear mixed models tested intervention effects. Results: While no significant reduction in problematic social media use or increase in self-efficacy was observed, the intervention group showed a significant reduction in daily screen time on their most problematic app by approximately 29 minutes (estimate=-29.35, SE 6.84, 95% CI -42.79 to -15.99; P<.001), and a significant decrease in perceived problematic smartphone use (estimate=-0.46, SE 0.18, 95% CI -0.80 to -0.11; P=.01). Conclusions: The Wellspent app demonstrated short-term efficacy in reducing problematic smartphone use. By allowing users to tailor interventions to their personal goals, the app shows promise as a self-directed tool to support healthier digital habits. Further research should explore long-term effects and feature-specific impacts.

In the recent years, studies on health consequences of smartphone usage time have increased, yet findings on the effectiveness of usage interventions remain unclear. This preregistered study investigates the effectiveness of a planning intervention to reduce total smartphone usage time. Additionally, it examines the interventions’ underlying mechanisms of self-efficacy, intention, action, and coping planning. A primary analysis of a randomized controlled trial, with data collected at three measurement points was conducted. Three cohorts of university students were recruited during the period prior to the end-of-term exams. A total of N = 787 participants were allocated to either an intervention condition (n = 389) or a control condition (n = 398). At baseline measurement (T1) the intervention condition formed up to three actions and three coping plans. Self-reported self-efficacy, intention, action, and coping planning as well as objectively measured smartphone usage were assessed up to a three-weeks follow-up. The effectiveness of the intervention and the mediating mechanisms were evaluated using linear mixed models. The analysis revealed no significant effect on total smartphone usage time. With respect to the interventions underlying mechanisms, results show a significant indirect effect of self-efficacy at T2, on a reduction in total smartphone usage time at T3 but no evidence for intention, action, or coping planning.

Background
Interventions targeting social media use show mixed results in improving well-being outcomes, particularly for persons with problematic forms of smartphone use. This study assesses the effectiveness of an intervention app in enhancing well-being outcomes and the moderating role of persons' perceptions about problematic smartphone use (PSU).

Methods
In a randomized controlled trial, N = 70 participants, allocated to the intervention (n = 35) or control condition (n = 35), completed weekly online surveys at baseline, post-intervention, and follow-up. Participants from the intervention condition received personalized full-screen nudges to reduce their social media app use. This secondary analysis focuses on the repeatedly assessed outcomes well-being, positive affect, negative affect, and perceived stress. Linear mixed models were computed.

Results
No significant time x group effects were found, but intervention condition participants reported higher well-being and lower negative affect and stress levels at follow-up. Only one significant moderation was found, indicating that participants reporting higher PSU levels benefited more from the intervention in reducing stress.

Conclusions
The intervention was partly effective and particularly beneficial in reducing stress among smartphone users with higher PSU, highlighting the need to tailor interventions. Present findings need to be replicated by future research using a larger sample size.