Medication nonadherence: health impact, prevalence, correlates and interventions

Figures & data

Figure 1. Illustration of the process of adherence to medication (light blue) and the process of management of adherence (dark blue). Reprinted from Vrijens et al. (2012).

Figure 2. Perceptions and Practicalities Approach (PaPA) incorporating opportunity and triggers. Reprinted from Horne et al. (2019).

Figure 3. Perceptions and Practicalities Approach – a detailed conceptual map of adherence. Reprinted from Horne et al. (2019).

Table 1. Methods for measuring medication adherence.

Method	Example	Advantages	Disadvantages
Direct
Observation	Adherence assessment is made by directly observing patients taking their medication. Widely used in the treatment of tuberculosis but as an intervention to improve adherence rather than a means of measuring adherence.	Accurate	Costly Inconvenient for patient and assessor
Biological assays	Usually, blood or urine samples are taken and analysed to detect levels of the drug/ drug metabolites.	Objective	Not available for all drugs Only assesses adherence in the time immediately preceding the assessment Hard to establish cut-offs as there are individual differences in the way drugs are metabolised Expensive May be inconvenient for patients Subject to ‘white coat adherence’ whereby patients take medication immediately before assessment.
Indirect
Pill count	Patients are asked to bring all their medication containers to their appointment. The remaining tablets are counted, and the percentage of prescribed doses taken is calculated.	Objective	Time consuming Dependent on patients bringing all their medication containers to appointments Pills may be thrown away to indicate adherence
Self-report	Patients are asked to describe their adherence either in an interview or through completion of a questionnaire or diary.	Inexpensive Simple Enables identification of nonadherent cohort (unlikely to be lying)	Dependent on patients accurately recalling medication use Response bias (social desirability and recency effects)
Repeat prescription/ pharmacy refill records	Records of when the patients collect or fill prescriptions are monitored. Actual collect/ fill date compared with date medication would have been needed if all doses had been taken as prescribed.	Inexpensive Prospective or retrospective assessment	Assumes a prescription is filled/filled prescription is taken Dependent on patients collecting/filling their prescription at the same place Crude indicator – patients are unlikely to collect/ fill prescriptions precisely when they need them
Electronic monitor	Caps of medication bottles contain a computer chip and record each time the container is opened. Caps are scanned and the data downloaded onto a computer.	Objective Enables detailed assessment of patterns of adherence, including exact timing of doses	Assumes medication is taken each time the container is opened Does not allow for patients decanting medication into other containers Expensive May require health professionals to decant medication into the containers Requires patients to bring containers with them to appointments for data to be downloaded May act as an intervention if people know they are being monitored

Reprinted from (Horne & Clatworthy, 2010).

Vrijens, B., De Geest, S., Hughes, D. A., Przemyslaw, K., Demonceau, J., Ruppar, T., Dobbels, F., Fargher, E., Morrison, V., Lewek, P., Matyjaszczyk, M., Mshelia, C., Clyne, W., Aronson, J. K., & Urquhart, J, ABC Project Team. (2012). A new taxonomy for describing and defining adherence to medications. British Journal of Clinical Pharmacology, 73(5), 691–705. https://doi.org/10.1111/j.1365-2125.2012.04167.x

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Horne, R., Cooper, V., Wileman, V., & Chan, A. (2019). Supporting adherence to medicines for long-term conditions. European Psychologist, 24(1), 82–96. https://doi.org/10.1027/1016-9040/a000353

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Horne, R., & Clatworthy, J. (2010). Adherence to advice and treatment. Health psychology (2nd ed.). John Wiley & Sons.

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Data availability statement

Data sharing is not applicable to this article as no new data were created or analysed in this study.