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 
).
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.
Older adults 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 older people (see Drug-Related Problems in Older Adults: 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.
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.
Health care providers may detect and help solve adherence problems. Health care providers should ask a patient how often they miss their drugs. A pharmacist may note that a patient does not obtain refills or that a prescription is being refilled too soon. The pharmacist could ask the patient, “When was the last time you took your medicine?" In reviewing prescription directions with the patient, a pharmacist may uncover a patient’s misunderstandings or fears and alleviate them. Pharmacists or other practitioners can recommend less complicated or less frequent dosing or substitute safe, effective, but less expensive drugs. Good communication among the patient and all the health care practitioners that provide care for that patient is important.
