A new review of existing research suggests that co-pays and caps on drug expenditures could keep crucial medications out of the hands of those who need them.

The review authors examined 21 studies that looked at a variety of prescription drug payment policies. Some had a cap, a maximum number of prescriptions or drugs that are reimbursed. Others policies required a co-payment with each prescription a cost-sharing method common in the United States where patients pay a portion of the medication cost.

Among insurers that tried to keep costs down through co-pays and caps, "reductions in drug use were found for both life-sustaining drugs and medications that are important in treating chronic conditions," said review lead author Astrid Austvoll-Dahlgren, a research fellow with The Norwegian Knowledge Centre for the Health Services.

This could have "adverse effects" and lead to higher costs to take care of patients who end up getting sicker, Austvoll-Dahlgren said. By contrast, "policies in which people pay directly for their drugs may be less likely to cause harm" if only non-essential drugs are included and if exemption safeguards are built into the policy, she said.

At issue is the best way for insurers to pay for medications. Should they encourage patients to use cheaper and more cost-effective drugs by instituting co-pays and caps? Or is it better for insurers to simply pay the full cost of medications?

The review appears in the latest issue of The Cochrane Library, a publication of The Cochrane Collaboration, an international organization that evaluates medical research. Systematic reviews draw evidence-based conclusions about medical practice after considering both the content and quality of existing medical trials on a topic.

Among the analyzed cost-sharing policies some included co-pays and caps, others set drug benefit ceilings in which patients pay for their medications up to a certain amount; above that level fees go down or disappear. A few policies combined various approaches.

One study examined a New Hampshire policy that limited reimbursement to three prescriptions for poor patients with chronic disease. A 1977 policy, in South Carolina, required a 50-cent co-pay for drug prescriptions.

The studies suggest that caps and co-pays reduced both the amount of medication used including life-sustaining drugs and medicine expenditures. However, the researchers deemed the studies "generally low to moderate" quality.

It is not clear if patient health suffered under the cost-sharing policies. Few of the studies looked at how the various payment systems affected overall health. The New Hampshire study found "adverse effects" when the cap was introduced, Austvoll-Dahlgren said, but other studies did not find an impact.

Austvoll-Dahlgren said getting access to medical records might have been a barrier to a thorough analysis of the effects of drug payment policies on health. Or, she said, researchers may not consider the health issue to be a priority.

The overall lesson, she said, is that policies designed to make people shoulder some of the cost of prescriptions could potentially make people sicker.

But Austvoll-Dahlgren said there may be a solution. "Policies in which people pay directly for their drugs may be less likely to cause harm if only non-essential drugs are included in these policies or exemptions are built into the policies to ensure that people receive needed medical care."

Richard Frank, a professor of health economics at Harvard Medical School whose research was mentioned in the review, said the findings are not surprising: "Yes, consumers do respond to prices."

He said the most sensible strategy for insurers may be to offer a tiered approach that makes patients pay a smaller co-pay for a generic drug and a larger amount for brand-name drugs.

Frank said the best approaches "don't force people into either stopping things entirely or making clinical decisions that are solely based on dollars and cents."

The worst money-saving strategies put limits on the number of drugs that patients can get or set limits on coverage, according to Frank. "They've been shown to not save that much money and create lots of bad outcome. Across the board, they're not very nuanced, and they tend to be more likely to get you in trouble."

The Cochrane Collaboration is an international nonprofit, independent organization that produces and disseminates systematic reviews of health care interventions and promotes the search for evidence in the form of clinical trials and other studies of interventions. Visit cochrane for more information.

Austvoll-Dahlgren A, et al. Pharmaceutical policies: effects of cap and co-payment on rational drug use (Review). Cochrane Database of Systematic Reviews 2008, Issue 1.

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