Macrophage migration inhibitory factor (MIF) is a pro-inflammatory cytokine that has been associated with various psychiatric disorders. MicroRNA-451a (miR-451a) can directly target MIF and down-regulate its expression in cells. However, the role of MIF and miR-451a in psychiatric patients treated with psychotherapeutic interventions is unknown. In this study, our aim was to investigate levels of MIF and its regulating miR-451a in patients with depression, anxiety or stress- and adjustment disorders who underwent mindfulness-based therapy or treatment as usual (TAU).