Adherence Barriers, Facilitators, and Root-Cause Analysis

This topic examines why people do or do not take medicines as agreed — the patient, regimen, condition, and system factors that act as barriers or facilitators — and the structured analysis used to identify the root causes of non-adherence. A central distinction is between unintentional non-adherence (forgetting, complexity) and intentional non-adherence (a deliberate decision shaped by beliefs and concerns).

Definition

Adherence barriers and facilitators are the modifiable and non-modifiable factors — spanning socioeconomic, health-system, condition-related, therapy-related, and patient-related dimensions — that decrease or increase the likelihood that a person takes medicines as agreed; root-cause analysis is the structured attempt to identify which factors operate for a given person or population.

Scope

The entry organizes the determinants of adherence, the role of medication beliefs, and the logic of diagnosing the cause before choosing a response. It is descriptive reference material and does not provide individualized advice for managing a specific patient's non-adherence.

Core questions

• Which factors most consistently predict non-adherence across conditions?
• How do intentional and unintentional non-adherence differ, and why does the distinction matter for response?
• How do beliefs about the necessity of, and concerns about, a medicine shape medicine-taking?
• How can the underlying cause of non-adherence be identified before an intervention is selected?

Key concepts

• Intentional versus unintentional non-adherence
• Necessity beliefs and treatment concerns
• Regimen complexity and pill burden
• Cost and access barriers
• Health literacy
• Side effects and tolerability
• Therapeutic relationship and trust

Key theories

Necessity-Concerns Framework

Proposes that adherence reflects an implicit weighing of beliefs in the personal necessity of a medicine against concerns about its potential adverse effects; the balance predicts intentional non-adherence and is measured with the Beliefs about Medicines Questionnaire.

WHO five-dimensions model

Frames adherence as determined by interacting socioeconomic, health-system, condition-related, therapy-related, and patient-related factors, countering the view that non-adherence is solely a patient problem.

Mechanisms

Barriers cluster across the WHO's five dimensions and act through two broad routes. Unintentional non-adherence stems from capability and opportunity limits — forgetting, complex regimens, high pill burden, cost, or poor access — and tends to respond to simplification and reminders. Intentional non-adherence stems from motivation and beliefs: when perceived concerns about a medicine outweigh perceived necessity, a patient may deliberately reduce or stop it. Identifying which route predominates is the purpose of root-cause assessment, because remedies for forgetting differ from remedies for doubt about a treatment's value.

Clinical relevance

Understanding the determinants of non-adherence underpins pharmaceutical care and adherence-support services. This entry describes the factors and the diagnostic logic as a body of knowledge; it is not guidance for assessing or treating any particular patient.

Epidemiology

Reviews of systematic reviews find that no single determinant dominates universally; adherence is multifactorial, and the relative weight of barriers varies by condition, regimen, and population. The WHO report emphasizes that condition- and system-level factors, not only patient choices, drive observed non-adherence.

Evidence & guidelines

Syntheses caution that because determinants are heterogeneous and context-specific, effective support generally requires identifying the operative barriers rather than applying a generic intervention; belief-based measures such as the Beliefs about Medicines Questionnaire help distinguish intentional from unintentional non-adherence in research and practice.

History

The view of non-adherence shifted from blaming patients toward a multidimensional account consolidated by the WHO's 2003 report. In parallel, Horne and Weinman's necessity-concerns work in the late 1990s gave a cognitive account of intentional non-adherence, and later syntheses such as Kardas and colleagues' review of reviews mapped the breadth of determinants.

Debates

Is non-adherence mainly a patient problem?

The WHO framework reframed non-adherence as also a property of the health system, condition, and therapy, challenging interventions that target only patient behavior while ignoring cost, complexity, and access.

Key figures

• Rob Horne
• John Weinman
• Przemysław Kardas
• Eduardo Sabaté
• Lars Osterberg

Seminal works

• sabate-2003
• horne-1999
• kardas-2013
• horne-bmq-1999

Frequently asked questions

What is the difference between intentional and unintentional non-adherence?

Unintentional non-adherence happens despite an intention to take the medicine — through forgetting, complexity, or access problems — whereas intentional non-adherence is a deliberate decision to reduce or stop a medicine, typically shaped by beliefs and concerns about it.

What is the Necessity-Concerns Framework?

It is a model proposing that medicine-taking reflects a balance between a patient's belief that a medicine is necessary and their concerns about its potential harms; when concerns outweigh perceived necessity, intentional non-adherence becomes more likely.