Pillbox intervention fidelity in medication adherence research: A systematic review

•Significant limitations exist in reports of pillboxes in adherence interventions.•Pillbox study translation to practice should rely on reported, not assumed intervention components.•It is important to assess how control groups adhere to the control condition.•Receiving or enacting treatments is as important as reporting attrition.•The five components of intervention fidelity are underreported in pillbox studies.•It is unclear how to best enact pillboxes to support medication adherence behaviors.