The findings from a randomized trial45
and dozens of observational studies indicate that lack of drug coverage strongly inhibits the use of prescription drugs, but there is less information on the other risk factors, especially those unrelated to financial burden. Furthermore, there has been no assessment of whether the risk factors identified for all-cause nonadherence also predict cost-related nonadherence as indicated by patients. In our review, we found empirical support for concluding that certain patients may be more susceptible to cost-related medication nonadherence than others, regardless of financial burden. Nearly all of the studies were cross-sectional, which limits the interpretation to only associations. Nevertheless, some of the associations remained consistent across different patient groups and in numerous studies with large sample sizes.
As others have found, not having prescription drug coverage emerged as a significant and robust risk factor for cost-related nonadherence. However, the protection afforded by drug coverage varied by the source, duration, and to some extent, the benefit design features. Medication costs, rather than drug coverage, was the more influential economic factor on CRN decisions. These findings are supported by studies using only insurance claims, which have shown average medication use decreases after increases in copayments even among people with the same type of drug coverage.8,22,23
The reviewed studies also established consistent links among low levels of physical health, mental health deficits, and CRN, and these effects persisted after controlling for economic factors. Individuals who have symptoms of depression or a heavy disease burden appear to be more susceptible to cost-related nonadherence, and this tendency cannot be explained by lack of drug coverage, poverty status, or monthly out-of-pocket drug costs.
We did not find sufficient evidence that patients fully understand the potential consequences of CRN on their health. To the contrary, the limited evidence suggested that perceptions of low health risk may predict CRN. It remains to be determined why so many patients apparently believe that skipping doses to reduce costs will not compromise the effectiveness of their treatment.
Physician relationships rated by patients as high quality and trustworthy greatly decreased the likelihood of CRN. However, discussions about medication costs with doctors, pharmacists, or nurses appeared as a marker of high risk. This latter finding, though, is likely due to the cross-sectional study designs.
Several limitations of this review should be noted. The assessment of CRN was based on self-report. In general, patients tend to understate nonadherence so our study populations were probably a subset of the true population.46
Furthermore, we did not know whether the reported nonadherence conflicted with the advice of prescribers or was trivial (i.e., one skipped dose). The cross-sectional study designs also confounded some of the findings and interpretations. There are high correlations, for instance, among contemporaneous measures of health status, medication costs, and polypharmacy. Thus, it is unclear if medication costs lead to cost-related nonadherence, which then leads to lower health status or if the causality order begins with worsening health. Lastly, only 2 of the reviewed studies35,43
examined patients under the age of 50, thereby, limiting the generalizability of this review to younger populations.
Future studies are needed that model the patient response to medication costs using standard measures and accepted theories of health care decision making. One challenge of this review was the wide variety of CRN measures (some without tested reliability and validity). Furthermore, this body of research lacked robust models for explaining the behavior. Piette’s conceptual framework for understanding CRN suggests that the response may be modified by multiple contextual factors, but it has never been formally tested. As a result, the studies reviewed here provided uneven coverage of potentially important components of cost-related nonadherence. Also, research on CRN would be improved by more studies of both subjective patient assessments and objective data sources such as administrative insurance claims. It would be valuable to understand the gap between what the drug coverage actually covers and what patients believe it covers.
Lastly, longitudinal studies that track patient perception of risk and financial pressures before the nonadherence decisions are made would provide more valid methods for identifying the most important factors that prompt or prevent CRN. The body of longitudinal research drawn from prescription claims has provided unequivocal evidence of population-level decreases in drug utilization after increases in cost-sharing.7,8,47
The next step is to identify the factors that enabled some patients to maintain their prescription drug regimen despite the cost increases.
What are the implications of this review for the new Medicare Part D benefit? Projections of the average Part D cost-sharing under standard benefit (without income subsidies) are $1,095 in 2006, $1,325 in 2007, and $1,357 in 2008.10
Moreover, these out-of-pocket costs can vary, as beneficiaries spend through the plan’s deductible, coverage gap (“donut-hole”), and catastrophic threshold.10
Some plans offer alternative benefit designs; however, the majority of Part D enrollees will face substantial and unpredictable medication costs. To put these numbers in context, the median income of households headed by someone aged 65 or older in 2004 was $24,509.48
Understanding and measuring the risk factors that moderate or exacerbate the impact of medication costs on adherence will be critical for explaining patient responses to the new drug benefit.