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Adherence to a Drug Regimen


Shalini S. Lynch

, PharmD, University of California San Francisco School of Pharmacy

Last full review/revision Jul 2019| Content last modified Jul 2019
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Adherence (compliance) is the degree to which a patient follows a treatment regimen. For drugs, adherence requires that the prescription be obtained promptly and the drug be taken as prescribed in terms of dose, dosing interval, duration of treatment, and any additional special instructions (eg, taking the drug without food). Patients should be told to alert their physician if they stop or alter the way they take a drug but they rarely do so.

Only about half of patients who leave a physician’s office with a prescription take the drug as directed. The most common reasons for nonadherence are

  • Frequent dosing

  • Denial of illness

  • Poor comprehension of the benefits of taking the drug

  • Cost

Many other reasons contribute to nonadherence (see table Causes of Nonadherence Causes of Nonadherence Causes of Nonadherence ).


Children are less likely than adults to adhere to a treatment regimen. Adherence is worst with chronic disorders requiring complex, long-term treatment (eg, juvenile diabetes, asthma). Parents may not clearly understand prescription instructions and, within 15 minutes, forget about half the information given by the physician.

The elderly adhere to treatment regimens as well as other adults. However, factors that decrease adherence (eg, inadequate finances, use of multiple drugs or drugs that must be taken several times a day) are more common among the elderly (see Drug-Related Problems in the Elderly: Lack of patient adherence Drug-Related Problems in Older Adults Drug-related problems are common in older adults and include drug ineffectiveness, adverse drug effects, overdosage, underdosage, inappropriate treatment, inadequate monitoring, nonadherence... read more ). Cognitive impairment may further decrease adherence. Sometimes a prescriber must be creative by picking a drug that is easier to use even though it may not be the first choice. For example, a clonidine patch applied weekly by a visiting nurse or family member may be tried for hypertension in patients who cannot adhere to a more preferable daily regimen of oral drugs.

The most obvious result of nonadherence is that the disorder may not be relieved or cured. Nonadherence is estimated to result in 125,000 deaths due to cardiovascular disorders each year in the US. If patients took their drugs as directed, up to 23% of nursing home admissions, 10% of hospital admissions, many physician visits, many diagnostic tests, and many unnecessary treatments could be avoided. In some cases, nonadherence can actually lead to worsening of disease. For example, missed doses or early cessation of antibiotic or antiviral therapy may lead to resistant organisms.

Pharmacists and nurses may detect and help solve adherence problems. For example, a pharmacist may note that a patient does not obtain refills or that a prescription is being refilled too soon. In reviewing prescription directions with the patient, a pharmacist or nurse may uncover a patient’s misunderstandings or fears and alleviate them. Physicians can alter complicated or frequent dosing or substitute safe, effective, but less expensive drugs. Communication among all health care practitioners that provide care for a patient is important.

Drugs Mentioned In This Article

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