This well-conducted review concluded that less cost sharing for patients with chronic diseases could improve their adherence, but the effects on clinical and economic outcomes were uncertain. These conclusions reflect the limitations in the evidence and are likely to be reliable, but the findings may have limited generalisability to non-insurance-based health care systems.

To determine the association between strategies to share costs between drug insurers and patients, and medication adherence, and clinical and economic outcomes, for patients with chronic diseases.

The following databases were searched, for English-language studies, in March 2013: MEDLINE, EMBASE, CINAHL, Cochrane Central Register of Controlled Trials (CENTRAL), and Current Controlled Trials. Relevant reference lists were searched. The full search strategy was reported.

Randomised controlled trials (RCTs), non-randomised controlled trials, controlled before-and-after (CBA) and interrupted time series (ITS) studies were eligible for inclusion. Studies had to assess the impact of drug insurance without cost sharing, or with a low level of sharing, as part of an insurance system, compared with higher out-of-pocket expenditure. Participants had to be adults with chronic disease: coronary artery disease, hypertension, diabetes, hypercholesterolaemia or cerebrovascular disease. Studies had to examine various cost-sharing strategies, including co-payments, coinsurance, fixed co-payments, deductibles and maximum out-of-pocket expenditure. Value-based insurance design and reference-based pricing studies were excluded. Eligible outcomes were medication adherence, clinical events (myocardial infarction, stroke, or death), quality of life, health care use and costs.

The included studies evaluated various drug insurance policy changes. Compared with the intervention groups, the control groups had higher out-of-pocket payments for the patient, and ranged from no drug insurance to a higher level of payment. Most studies focused on elderly patients, and most studies were conducted in the USA or Canada.

Two reviewers independently selected studies, with any disagreements resolved by consensus or in consultation with a third reviewer.

The quality of the studies was evaluated using the Cochrane risk of bias tool, for randomised controlled trials, and the Cochrane Effective Practice and Organisation of Care (EPOC) criteria, for non-randomised trials, controlled before-and-after studies, and interrupted time series studies.

Two reviewers independently assessed quality, with disagreements resolved by consensus or in consultation with a third reviewer.

The data were extracted for medication use and adherence. Two reviewers independently extracted the data, with any disagreements resolved by consensus or in consultation with a third reviewer.

The heterogeneity among the studies precluded any meta-analysis. The studies were synthesised in a narrative.

Eleven studies were included in the review; two were separate reports of one RCT, four were ITS studies, and five were CBA studies. The sample size ranged from 3,958 to 470,029. The RCT was judged to be of moderate quality. The ITS studies were judged to be of high quality, but the CBA studies were judged to be of poor quality.

Three studies compared patients with no drug coverage, with patients who had stable uncapped drug coverage that remained unchanged before and after the implementation of Medicare Part D. The results showed that, in patients aged 65 years or older with hypertension, hypercholesterolaemia, diabetes or a combination of these, drug insurance increased adherence to guideline treatment (OR 1.19 to 2.36, depending on condition treated), compared with no drug insurance.

Seven studies evaluated the effects of varying levels of co-payment. There was variation in the association between patient co-payments and medication adherence across studies. It ranged from no difference to significantly lower adherence, depending on the amount of the co-payment.

Clinically relevant outcomes were reported in two studies. A subgroup analysis of one study reported that full insurance was associated with a statistically significant decrease in diastolic blood pressure (-1.9mmHg, 95% CI -3.5 to -0.3), compared with the cost sharing strategies. Another study found no significant difference in death, myocardial infarctions, heart failure or angina after changing from a small co-payment to 25% co-insurance.

Further results on the impact of deductibles, changes in the maximum out-of-pocket limit, and coverage gaps were reported in the paper.

One study reported that a change from a minimal co-payment (two Canadian dollars – CAD – per prescription; annual maximum of CAD 100) to 25% co-insurance, with a CAD 750 annual maximum out-of-pocket expenditure, resulted in no apparent change in medication use. Further results were reported.

Less cost sharing for patients with chronic diseases could improve their adherence, but its effect on the clinical and economic outcomes was uncertain.

This review question was clear, and the inclusion criteria were adequately specified. Various relevant sources were searched. The search was restricted to English-language studies, so other relevant studies may have been missed. The review process contained appropriate steps to minimise errors and bias. Study quality was assessed, using appropriate criteria. Half of the studies were of moderate-to-high quality, but the rest were poor. Given the variation among the studies, a narrative synthesis was appropriate.

This review was generally well conducted. The authors' conclusions reflect the limitations in the evidence and are likely to be reliable, but the findings may have limited generalisability to non-insurance-based health care systems.

Practice: The authors stated that policy makers should be aware that co-payments and deductibles reduce the cost for the payer, but could reduce medication adherence and ultimately health outcomes, particularly for those of lower socioeconomic status.

Research: The authors did not state any implications for research.

Funded by Alberta Innovates - Health Solutions, Canada.