The phrase medication adherence refers to the extent to which persons given a pharmacologic treatment actually use it in the way the prescribing clinician intends, for example, taking an antibiotic twice every day with a 12-hour interval between doses. Medication adherence is a complex phenomenon related to characteristics of the person using the medication, his or her beliefs about it and its effectiveness, the milieu in which he or she lives, the characteristics of the treatment (frequency of doses, presence of side effects), and external mechanisms used to remember to take medication, such as pill boxes or automatic reminder devices. Park has argued for the integration of these areas in a broader model for understanding medication adherence.
Several characteristics of the person prescribed a medication may affect his or her adherence to its use. Cognitive function, mood, age, socioeconomic status, and cultural background are all related to medication adherence. Poorer cognitive function has been related to lower levels of adherence, and more complex cognitive functions such as executive abilities may be related to more complex adherence behaviors. Depression has a negative effect on adherence. Although increasing age is commonly thought to be associated with poorer adherence, several studies have shown that older adults actually have better adherence than their younger counterparts. African Americans have been shown to have poorer adherence to some medications even after controlling for factors such as access to care and socioeconomic status.
Individuals’ beliefs about the medication, including the extent to which it is useful for the condition for which it is given, have important effects on adherence. Several theories have been proposed to explain the relation between beliefs and behavior, including Janz and Becker’s health belief model and Ajzen’s theory of planned behavior as well as others. In addition to beliefs about effectiveness, beliefs about the seriousness of the treated condition can affect adherence. Adherence to a medication believed to be ineffective or prescribed for a condition that is viewed as not very serious (e.g., a medication for mild insomnia) is likely to be lower than for an effective medication given for a life-threatening condition.
Characteristics of the treatment regimen may also affect adherence. Regimen complexity (number of medications, number of doses, whether doses must be taken a certain time before meals or should be taken with food) plays a role in adherence. In some health conditions, such as HIV-related diseases, regimen complexity may interact with cognitive status. The presence or absence and severity of adverse effects (side effects) have an important negative impact on medication adherence.
Beliefs of caregivers, significant others, or family members about the medication’s effectiveness and the condition for which it is prescribed are likely to affect adherence. Caregiver or family beliefs may be especially important for conditions that affect cognitive or functional status and thus require external information or caregiver interventions (e.g., Alzheimer’s disease, congestive heart failure, HIV-related dementia).
Individuals’ medication adherence is a complex behavior that must occur over long periods of time. Maintenance of the behavior consistently over such intervals can be supported by mechanical devices such as pill boxes that can be filled a week or month at a time and thus provide passive prompts to the treated individual on a daily basis. Active prompts can be provided via alarm clock-based timers, computer-based automated reminding via home telephones or pagers, and in-home checks and reminders by home healthcare workers.
Medication adherence is vitally important in the treatment of disease. To the extent that a condition is affected by medication, adherence to the regimen may be critical and even life sustaining. An example of the critical importance of adherence is provided by the effects of adherence on antiretroviral treatments for HIV infection. High levels of adherence are required for successful suppression of viral replication and improved immune system functioning. Importantly, intermittent or low levels of adherence may result in the creation of medication-resistant viral strains. Adherence is related to likelihood of hospitalization in some conditions, such as congestive heart failure, where close adherence to treatment can affect the status of the cardiovascular system. Medication adherence has been related to various healthcare outcomes, including medication adverse events, hospitalization, and healthcare costs.
Perhaps most interestingly, high levels of adherence are related to healthcare outcomes independent of other treatment interventions. Studies show that high levels of adherence even to placebo may be associated with better health outcomes than intermittent adherence to active medication. A review of these studies has led some to propose a “good adherer” type that may be associated with a variety of healthcare behaviors such as diet and exercise. According to Joynt and colleagues, it is likely that medication adherence and other behaviors interact with physical disease factors to produce good or poor healthcare outcomes.
Interventions to Improve Adherence
Each of the areas associated with medication adherence has been the target of interventions to improve adherence. Interventions that target persons’ beliefs about medication effectiveness and condition seriousness have been useful in improving adherence, especially when the messages are made personally relevant to the person taking the medication. Family or social milieu interventions may also be effective in improving adherence. Changes in treatment characteristics, such as minimizing regimen complexity and reducing the impact of adverse medication effects, can improve adherence. External supports or reminders, whether passive or active, are also effective in improving medication adherence. Computer-based interventions may become increasingly important in improving medication adherence, because they can make labor-intensive interventions, such as providing individually tailored information, economically feasible.
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