About 90 million adults in the United States misunderstand at least some of the instructions on prescription drug labels, according to the Institute of Medicine. (bigstockphoto)

We rely on drug labels and package inserts for important instructions and warnings about the drugs we take. But when Consumer Reports staff members recently picked up prescriptions from five national pharmacy chain stores, they found bottle labels and patient information sheets that were both difficult to read and lacking in information.

About 90 million adults in the United States misunderstand at least some of the instructions on prescription drug labels, according to the Institute of Medicine. And the Food and Drug Administration has found that only 75 percent of the leaflets included with prescriptions meet the agency’s minimum recommended criteria for usefulness. Small print, technical language and incomplete instructions might play a role in the roughly 500,000 preventable outpatient medication errors that occur nationally each year.

Consumer Reports’ staff members filled prescriptions for 5 milligrams of warfarin, a common generic blood thinner, at Costco, CVS, Target, Walgreens and Wal-Mart stores near their offices in Yonkers, N.Y. Although the findings are not nationally representative for each chain, they do provide a glimpse into common issues consumers may face.

Warfarin is the second-most-likely prescription drug to cause serious adverse reactions leading to emergency room visits, so the CR staffers expected fairly clear and moderately consistent warnings and instructions among all five prescriptions. Instead, they found that critical information was confusing, misleading, buried or absent.

Most bottle labels were fairly easy to read, but the typeface on the Costco label was smaller than experts advise. And Costco, Walgreens and Wal-Mart did not list the common brand name, Coumadin, in addition to the generic name, warfarin.

The Target bottle clearly listed four warnings about warfarin. The Walgreens bottle also had four, CVS’s listed three, Costco’s mentioned two and Wal-Mart’s, surprisingly, had none. Bottles from two later visits to Wal-Mart had three warnings each.

As for the patient information sheets, only Costco provided the FDA-approved medication guide that is required for some drugs, including warfarin. CVS and Target representatives said that their pharmacies automatically printed medication guides for patients. But they weren’t included in the prescriptions that were received. Walgreens and Wal-Mart didn’t respond to Consumer Reports’ queries.

All five pharmacies did provide their own patient information materials containing drug information, but they differed from the federally mandated, FDA-approved medication guide, which should have been included in the packages.

One difference involved warfarin’s possible side effects, which, according to the official FDA guide, include life-threatening bleeding problems; skin-tissue damage; “purple-toes syndrome,” which can lead to amputation; allergic reactions; liver problems; low blood pressure; swelling; low red blood cell counts; paleness; fever; and rashes. But the inserts from Walgreens, Wal-Mart and Target reported under the heading “possible side effects” that there are “no common side effects with the proper use of this medicine.” Those inserts instead included a list of serious symptoms and “unusual effects” — shortness of breath and bloody stool or urine among them — and followed up with a caveat referring patients to their doctor for information about other possible side effects.

None of the pharmacy-provided inserts listed additional side effects that can be caused by warfarin, such as gas, tiredness, hair loss, change in the way things taste, and chills.

All the patient information materials did include the drug’s “black box” safety warning that mentioned “severe and sometimes fatal bleeding” and other cautions. And all had information on how food, supplements and drugs can cause interactions. While all that was helpful, information in the inserts from Costco, CVS, Target and Walgreens was in a tiny typeface, and Walgreens’ insert had tight spacing between lines, making it difficult to read. Wal-Mart’s insert had larger lettering and was spread over four pages. And none seemed to be written in plain English.

Bottom line: Don’t rely solely on labels and inserts for information about the medication you take; talk with your doctor and pharmacist.

Copyright 2011. Consumers Union of United States Inc.