Adherence to Treatment Regimens

Adherence, also known as compliance, to treatment regimens refers to the degree to which a patient's management of his or her daily regimen corresponds to the regimen prescribed by the health care provider. Thus, if a patient is prescribed one pill twice a day and takes one pill twice a day, the match between behavior and prescription is 100%—adherence is 100%. If that same patient takes one pill once a day, the match is accurate 50% of the time—adherence is 50%. Similarly, if the patient is prescribed exercise three times a week for 30 minutes but exercises once a week, that patient would be 33% adherent.

Problems with adherence to treatment regimen have been known for centuries. Indeed, Plato commented on poor adherence to recommended treatment based on observations made while accompanying his physician brother on patient visits. Efforts to study adherence to medical treatments began in earnest in the late 1960s, with studies of interventions beginning in the mid-1970s. The first conference on patient adherence (compliance) was held in Canada in the mid-1970s. Since that time considerable effort has gone toward understanding this phenomenon and to a lesser extent to exploring strategies to remediate it.

Adherence problems may arise with any treatment regimen. Indeed, adherence rates to medication, diet, and exercise regimens have all been reported to average about 50%. This reflects substantial deviation from optimal therapies, a deviation that results in more than $150 billion in added costs annually (Grahl, 1994); the added costs are the result of additional treatment requirements, preventable hospitalization, management of disabilities, and the burden of early retirement.

In addition to added costs to the health system, poor adherence may have significant negative clinical consequences. Poor adherence has been associated with disease progression and with the development of complications. It has even been associated with loss of transplanted organs and death. Furthermore, poor adherence has been associated with the development of treatment-resistant organisms in such conditions as HIV/AIDS, ear infections, and tuberculosis. Failure to adhere to immunization recommendations has been associated with preventable disease, such as measles. Undetected poor adherence prevents the assessment of treatment adequacy and clinical efficacy. This often results in changes in treatment or in treatment dosing.

Poor adherence not only has a negative impact on clinical outcomes, it also has a negative impact on clinical trials. When subject adherence is low in research, larger sample sizes are required to provide adequate power to evaluate treatment efficacy. This can significantly increase the cost and time to complete studies. Where this compensation is not done, treatment effectiveness may be underestimated. Poor adherence may reduce the ability to detect side effects from treatment, thus overestimating safety and/or underestimating risks or adverse effects. Thus, poor adherence has the potential to mask true evaluations of new treatments, thus impacting treatment itself.