People don't always get their prescription filled and it's not clear just how widespread a problem this is. Past studies have suggested that the total number of prescriptions left unfilled could be less than 2% or as high as 20%.

An editorial in the Annals of Internal Medicine says that it's about time someone found out.

The most obvious reason prescriptions are abandoned is that people can't afford them. But there are many other reasons, including drug recalls.

Prescriptions not brought to a pharmacy or not picked up from the pharmacy are collectively called prescription abandonment. The most obvious reason prescriptions are abandoned is that people can't afford them. But there are many other reasons a prescription might be abandoned. People may be worried about side effects. Or they may not thoroughly trust that the prescription will be helpful. The many highly publicized recalls of drugs over the past few years may also play a part.

Nobody really knows. Studies have been few and far between.

Michael D. Murray, a professor of pharmacy at Purdue, and Jeff Harrison, a professor of pharmacy at the University of Auckland, have conducted research that suggest ways to lower prescription abandonment. But to do so requires more information on how widespread the phenomenon is and what its major causes are.

Dr. Murray and Dr. Harrison are largely concerned about the issue of cost, particularly in the United States, where insurance may or may not pay for a particular prescription. Doctors are often unaware of how much a patient will have to spend for a prescription. A high-priced prescription can lead to a patient having to choose between buying drugs or buying food. They think that better collaboration between doctors and pharmacists could help minimize sticker shock at the pharmacy. If a doctor knew that the high cost of a prescription might lead to a patient not filling it, they might prescribe a cheaper alternative. A prescription that ends up unfilled does no one any good.

But what's needed most is better information. Past studies have often looked at the abandonment of one particular type of drug and generalized that to all prescriptions. That's one reason for the wide spread in study results. A figure of 20% indicates a major problem, 2% a much smaller problem.

Dr. Murray and Dr. Harrison call for further studies to clarify the scope of the problem. It's hard to solve a problem when you don't even know how big it is. They also call for studies that look at how much of an effect prescription abandonment has on peoples' health.

The editorial appears in the November 16, 2010 issue of the Annals of Internal Medicine.

Michael D. Murray, PharmD, MPH is Professor of Pharmacy and Chair of Medication Safety at Purdue University College of Pharmacy. He is also a research scientist at the Regenstrief Center for Healthcare Improvement and Research Executive Director of the center.

Jeff Harrison, Ph.D. is a senior lecturer in pharmacy at the Auckland University School of Pharmacy, Auckland, New Zealand.