Purpose - As the number of social media users continues to rise globally, a heated debate emerges on whether social media use improves or harms mental health, as well as the bidirectional relation between social media use and mental health. Motivated by this, the authors' study adopts the stressor-strain-outcome model and social compensation hypothesis to disentangle the effect mechanism between social media use and psychological well-being. The purpose of this paper is to address this issue.

Design/methodology/approach - To empirically validate the proposed research model, a large-scale two-year longitudinal questionnaire survey on social media use was administered to a valid sample of 6,093 respondents recruited from a university in China. Structural equation modeling was employed for data analysis.

Findings - A longitudinal analysis reveals that social media use positively (negatively) impacts psychological well-being through the mediator of nomophobia (perceived social support) in a short period. However, social media use triggers more psychological unease, as well as more life satisfaction from a longitudinal perspective.

Originality/value - This study addresses the bidirectional relation between social media use and psychological unease. The current study also draws both theoretical and practical implications by unmasking the bright-dark duality of social media use on psychological well-being.