<p>Despite the usefulness of smartphones, some users engage in problematic smartphone use (PSU). Digital interventions may be offered for preventing and reducing PSU. This study evaluated the effects of two smartphone-based interventions among adolescents. Grounded in nudge theory, the focus function allowed users to hide smartphone applications (apps) for a selected length of time, while the feedback function provided a social comparison of the smartphone use of the user and other users. In total, 305 adolescents with Android smartphones were randomly allocated to the focus-function group, feedback-function group or control group. Participants used their smartphones as usual during the two-week baseline period, followed by the one-week update period and a four-week intervention period. The primary outcome was self-reported PSU at the end of the intervention period. The secondary outcomes were self-reported smartphone use time during weekdays and log-reported smartphone use time and frequency. The results showed reduced self-reported PSU both in the focus-function and feedback-function groups, Cohen's d = -0.32, 95% CI [-0.63, -0.008], Cohen's d = -0.36, 95% CI [-0.66, -0.06], respectively. The log-reported smartphone use frequency was also reduced in the focus-function and feedback-function groups, Cohen's d = -0.16, 95% CI [-0.07, -0.25], Cohen's d = -0.32, 95% CI [-0.23, -0.41], respectively. The findings suggest that both utilizing time-outs from nonessential apps and engaging in social comparison lower PSU and smartphone use frequency with small effect sizes. These functions may be noncoercive interventions for preventing and reducing PSU.</p>