<p>Medication non-adherence remains a persistent and critical challenge among kidney transplant recipients, who demonstrate higher rates of non-adherence than other solid organ transplant populations. Given the associated risks of graft rejection, graft loss, and mortality, a clearer synthesis of underlying psychological factors is needed. This systematic review synthesized evidence on psychological factors associated with self-reported medication non-adherence among adult kidney transplant recipients, integrating quantitative and qualitative research to capture patients’ perspectives. </p><p><?noindent??>Following Joanna Briggs Institute guidelines, five electronic databases (Embase, PubMed, PsycINFO, Scopus, and Web of Science) were searched from inception to 5 May 2026. Eligible studies included quantitative and qualitative research involving adult recipients. Methodological quality was appraised using the Mixed Methods Appraisal Tool, and findings were integrated using a convergent integrated approach. </p><p><?noindent??>Forty-four studies comprising 11,180 participants were included. Non-adherence prevalence ranged from 12.0% to 89.2%. Four overarching themes were identified: psychological distress, perceptions and beliefs, coping strategies, and social-contextual factors. Depressive symptoms and low social support were the most consistent correlates. Qualitative findings highlighted emotional burden, stigma, and regimen complexity as additional barriers. </p><p><?tk 0?><?noindent??>Medication non-adherence is multifactorial and context dependent. Integrating psychosocial screening and patient-reported outcomes into routine transplant care may improve adherence and long-term graft outcomes.</p>