Can the investigators create an effective way to improve adherence to immunosuppressant medication and reduce rejection, graft loss, and death in adolescents and young adults who have undergone kidney or liver transplantation? The investigators' mobile technology intervention uses real-time electronic pillbox-assessed dose timing and text message prompts to address antirejection medication nonadherence when nonadherence is detected.

Over 1/3 of adolescents and young adults who have undergone kidney or liver transplantation are nonadherent to antirejection medicines, accounting for shockingly high rates of infections, rejection, graft loss, and even death. Recently, the American Society of Transplantation highlighted real-time adherence intervention as top priorities to address antirejection medication nonadherence, but these evidence-based intervention tools do not exist. The investigators aim to answer the American Society of Transplantation's call and fill these critical gaps in nonadherence management for adolescents and young adults with kidney or liver transplant. Specifically, electronic pillboxes yield valuable real-time daily dosing data to guide interventions for adolescents and young adult kidney or liver transplant recipients, but existing interventions have not optimally leveraged these devices' capabilities. Just-in-time adaptive interventions delivered via mobile device (i.e., Smartphone or tablet) are cutting-edge approaches that fully incorporate adolescents and young adults' daily dose behavior to automatically deliver tailored intervention content exactly when adolescents and young adults need it most. The investigators piloted a promising static medication adherence support text message intervention based on the COM-B model, a well-established behavioral health intervention model, which will be modified into a just-in-time adaptive intervention for adolescents and young adult kidney or liver transplant recipients. Given that 95% of adolescents and young adults in the USA own smartphones, the investigators hypothesize that the investigators' intervention will improve on-time dosing and reduce rejection, graft loss, and death. The investigators believe that providing adherence support text messages or praise text messages will result in a higher proportion of adolescents and young adults taking the next dose and maintaining improvements in adherence post-intervention. In summary, the investigators' just-in-time adaptive intervention leverages real-time electronic pillbox-assessed dosing behavior and Smartphone text messaging capabilities to address tacrolimus or sirolimus nonadherence when nonadherence is detected.

Inclusion Criteria:

• Adolescents and young adults (13-25 years old) who underwent kidney or liver transplantation at least 6 months prior to enrollment
• Currently prescribed tacrolimus or sirolimus.

Exclusion Criteria:

• Currently receiving dialysis
• Hospitalized for duration of study
• Significant developmental or cognitive delay
• No access to a mobile device that supports text messaging
• Decline to use electronic pill box to monitor daily medication adherence
• Non-English speaking
• If a participant meets inclusion criteria, enrolls in the study, and experiences graft failure potentially leading to dialysis in the case of kidney transplant recipients, the participant will be given the option to continue in the study if they remain on tacrolimus or sirolimus.

Data from this study will be shared in a de-identified form (i.e., clean, de-identified electronic database) upon request.

Upon request

Data from this study will be shared in a de-identified form (i.e., clean, de-identified electronic database).