PATIENT ADHERENCE TO PRESCRIBED PHARMACEUTICALS – An analysis based on Swedish real-life data

Low patient adherence to prescribed pharmaceutical therapies attenuates treatment benefits and impedes health care effectiveness. This widespread and persisting problem is a public concern attracting global attention from policy makers and health managers. Despite a large literature, the mechanisms determining the individual’s decision process regarding adherence behavior is not yet well understood.

This study analyses patient adherence to prescribed pharmaceuticals within the demand-for-health mode. Despite being fundamental when economists analyze individual health behavior, the model has not earlier been used to explain patient adherence to pharmaceuticals. This paper adds two features to the original model. First, it assumes that the prescriptions are correctly prescribed so that adherence follows the physiological optimal quantity constraint. This implies that any deviation from the prescribed treatment plan is penalized by generating less health investments than feasible. Second, it assumes that the rate at which health investments transform to actual health depends on the characteristics of the specific pharmaceutical (i.e. its ability to interact and modify human biological systems) and patient characteristics, which determine the specific patient’s biological response to treatment. Besides characteristics such as gender and general health, the manifestation of specific health conditions may affect the patient’s biological response to pharmaceutical treatment making adherence more or less important. Thus, by modifying the health penalty size for deviating, the specific health conditions change the health benefits of adhering.

For cardiovascular management, an earlier manifested heart disease or a prolonged hypertension spell is specific health conditions augmenting the health penalty size for deviating from prescribed pharmaceuticals with selective beta receptor blocker, ace inhibitors, angiotensin receptor blockers and diuretics. Correspondingly for mental illness treatment, an earlier manifestation of anxiety or depression augments the health penalty size for deviation from antidepressants. As a higher a health penalty implies a higher marginal health benefit of adherence, theory predicts that these specific health conditions increase adherence to the corresponding regimens.   

For the empirical analysis, the paper uses a dataset containing the 2004-2005 year’s wave of Swedish Survey of Living Conditions (ULF) merged with the Swedish Prescribed Pharmacy Register (SPPR) from July 2005 through November 2007. Consisting of a national representative sample of approximately 10,000 adults, respondents in ULF were interviewed about living conditions, health and socioeconomic circumstance and answers were complemented with register data on, for instance, income, tax transfers and in-patient hospitalization. The nation-wide SPPR register contains information on all pharmacy dispensed pharmaceuticals with prescription and includes the patient’s unique prescribed daily dosage regimen. This data enabled us to assess 18 month adherence to a set of pharmaceuticals commonly used in the long-term treatment of mental illness and cardiovascular diseases.  

Controlling for general health, socioeconomic and demographic factors, the empirical analyses show that specific health conditions associate positively with adherence. The positive association implies that individuals deviate less to prescribed pharmaceutical treatments when the marginal health benefit of adherence is higher. This finding is important when design interventions aiming at improving long term adherence to pharmaceutical regimens.