Background: Little is known about weekly variability in medication nonadherence both between and within persons.
Purpose: To characterize medication nonadherence across repeated, closely spaced occasions.
Methods: This prospective cohort study comprised four unannounced telephone assessment occasions, each separated by approximately 2 weeks. On each occasion, adult outpatients taking at least a single antihypertensive medication completed a measure of extent of, and reasons for, nonadherence.
Results: Two hundred and sixty-one participants completed 871 (83%) of 1,044 occasions. Nonadherence was reported on 152 (17.5%) of 871 occasions by 93 (36%) of 261 participants. The most commonly endorsed reasons for nonadherence were forgetting (39.5%), being busy (23.7%), and traveling (19.7%). Among 219 participants completing at least three occasions, 50% of the variability in extent of nonadherence was a result of within-person fluctuations, and 50% was a result of between-person differences.
Conclusion: Interventions to reduce nonadherence should be informed by variability in the extent of nonadherence and specific reasons for nonadherence.
Keywords: adherence; compliance; hypertension; intraindividual variability.