In medicine, compliance—often called adherence—refers to the extent to which a patient follows health-care recommendations, particularly taking prescribed medications at the dose, time and frequency advised. Modern practice favors the term adherence to emphasize the patient's role and concordance to describe collaborative decision-making between clinician and patient. Compliance is central to successful management of chronic diseases such as asthma, diabetes and hypertension, where ongoing treatment prevents complications.

Definitions and scope

Non-adherence covers a range of behaviours: not filling an initial prescription (primary non-adherence), missing doses or taking incorrect amounts (secondary non-adherence), taking medicines at the wrong times, or stopping therapy prematurely. The consequences differ by condition and drug: for some short courses the impact is limited, while for many long-term therapies poor adherence leads to worse outcomes and higher health-care use.

How adherence is measured

Measurement methods vary in precision and practicality. Common approaches include patient self-report and questionnaires, pill counts, pharmacy refill or claims data, and electronic medication monitors or smart packaging. Self-report is inexpensive but prone to overestimation; pharmacy data can show refill behaviour but not ingestion; electronic monitors record container opening and provide detailed patterns but add cost and complexity. Results from controlled clinical trial settings often overstate adherence compared with routine care.

Factors influencing adherence

Adherence is multifactorial. Factors associated with poorer compliance include:

  • Patient-related: limited health literacy, forgetfulness, cognitive impairment, depression, or personal beliefs about medicines and illness.
  • Therapy-related: complex regimens, multiple daily doses, adverse effects, difficult formulations or frequent monitoring requirements.
  • Condition-related: asymptomatic phases (for example early hypertension) or variable symptoms that reduce perceived need for treatment.
  • Health system: poor clinician–patient communication, fragmented care, limited follow-up and access barriers.
  • Socioeconomic: medication cost, transportation, social support and competing life priorities.

Clinical and public health consequences

Worldwide, non-compliance is a major obstacle to effective care. The World Health Organization has emphasized that adherence to long-term therapies is generally suboptimal; older estimates suggested that only about half of patients with chronic illness in developed settings follow treatment recommendations. Poor adherence contributes to avoidable disease progression, increased hospital admissions, reduced quality of life and greater overall health-care costs.

Strategies to improve adherence

Interventions that improve adherence combine education, behavioural support, regimen simplification and system changes. Examples include:

  • Regimen simplification: once-daily dosing, fixed-dose combinations and reducing pill burden.
  • Clear counselling and written information about benefits and side effects to set realistic expectations.
  • Reminders and aid tools: alarms, smartphone apps, pillboxes, blister packs and automated refill reminders.
  • Clinical approaches: shared decision-making, regular follow-up, motivational interviewing and tailored adherence counseling.
  • System-level actions: reducing cost barriers, improving pharmacy access, and integrating medication management into chronic care models.

Special considerations and controversies

Different populations present particular challenges: older adults may have polypharmacy and cognitive issues, children depend on caregivers, and people with mental illness often need extra support. Ethical questions arise around monitoring adherence electronically and how data should be used. Technologies and digital interventions show promise but must be acceptable, affordable and equitable.

Resources and further reading

Practical resources for clinicians and patients include treatment guides and medication management tools (treatment guides), disease-specific information and support groups (condition resources), clinical practice materials and protocols (clinical resources), and programs addressing long-term care delivery (chronic care models). Condition-focused initiatives, for example in asthma, often combine education, self-management plans and adherence support. Ongoing research continues to refine reliable measurement and to assess which interventions produce sustained benefit in routine practice (medication management).