Introduction: University life can induce a lot of stress, which leads to mental health problems for some students. Many interventions that are used to reduce stress and its impact share acceptance of negative experiences as their core. However, the unique contribution of acceptance remains unclear. The current project will therefore examine the efficacy, mediators, and moderators of a brief acceptance intervention in a student population.

Method: First, data from a pilot study will be explored. Then, data from a randomized trial will be analysed, wherein participants (n = 116) were allocated to the intervention or to psychoeducation about acceptance and stress. They were measured before and after this. The main outcome was psychological well-being. Mediator analyses were conducted with acceptance and interoceptive awareness, and moderator analyses included adherence to home practice, neuroticism, and experience with mindfulness.

Results: In the randomized trial, the interaction effect between condition and time was significant for psychological well-being (d = 0.56, p = 0.003), but not for secondary outcomes. Estimates of the mediating effect of acceptance (-0.63, 95% CI [-1.48, 0.00]) and interoceptive awareness (-0.30, 95% CI [-0.99, 0.26]) did not reach statistical significance. Moderator analyses did not yield significant moderators.

Discussion: Our brief acceptance intervention increased participants’ psychological well-being with a medium effect size. The pilot study confirmed our conceptualization of the intervention, but mediator analysis failed to confirm acceptance as a working mechanism. Limitations include the short timeframe of our study and the conceptual overlap between acceptance and mindfulness. Despite this, the study underlines the importance of acceptance and provides a short and focused intervention.