<p>Problematic social media use negatively impacts undergraduate students’ mental well-being and academic performance. While abstinence interventions are promising, previous research has yielded inconsistent findings, possibly due to the challenging implementation of complete abstinence and the short intervention periods that overlook long-term effects. This study evaluated the effectiveness of a flexible social media abstinence intervention, requiring self-determined 2.5-hour breaks from social media four times a week. A total of 105 undergraduate students from China completed a three-week experiment. The flexible abstinence intervention was compared to a fixed abstinence intervention (six hours of abstinence during fixed periods four times a week) and a self-monitoring control group reporting daily experiences without abstaining from social media. Results showed that all three groups experienced increased life satisfaction and academic engagement, along with decreased perceived stress. Specifically, the abstinence interventions uniquely decreased fear of missing out and increased satisfaction with offline relationships and autonomy over social media use. The flexible abstinence intervention demonstrated a 90% compliance rate, suggesting that this approach was acceptable in the present sample. Overall, these findings indicate that flexible abstinence may represent a feasible intervention option for addressing problematic social media use among undergraduate students.</p>