When a patient's prescription for NuvaRing, a birth-control device, was incorrectly refilled with Estring, a device that treats menopause symptoms, the patient mistakenly became pregnant. Another patient's prescription for Fentanyl, an opioid pain medication, was called in to a pharmacist who heard Sufentanil (a pain medication that's 5 to 10 times more powerful). The pharmacist filled that prescription instead, and the patient needed cardiopulmonary resuscitation after taking it. These are just two of the thousands of examples of potential and actual drug errors reported voluntarily from 2002 through 2006 by health-care facilities and pharmacies nationwide and published in a 2008 report by the United States Pharmacopeia (USP), an official public standards-setting authority for all prescription and over-the-counter medicines. Though pharmacy personnel were responsible for many errors, pharmacists identified, prevented, and reported errors more than any other staff.

Since 2004 the number of confusing pairs of drug names has nearly doubled. And to make matters worse, errors are compounded by labels that look alike, poor physician penmanship, and sloppy pronunciation when phoning in drug orders.

In response to this growing problem, the USP is working with drug companies, policy makers, health-care facilities, and pharmacies on ways to protect the public. They recommend that each prescription indicate the reason for taking the drug, and when possible, they propose changing the names of drugs that have led to dangerous and repeated mix-ups.

You can protect yourself and your family from drug errors by taking the following precautions:

• When your doctor prescribes a drug, ask him or her to print the name and dosage for you, then spell it back aloud. If it's a brand-name drug, make note of the generic name as well.
• Ask your doctor to briefly note the drug's intended purpose on the prescription form. That will enable the pharmacist to make sure the drug is for the right purpose.
• Consult the USP's Drug Error Finder tool to find the names of drugs that are typically confused with your prescription.
• Don't leave the pharmacy until you've checked the label on your prescription. If a refill doesn't look the same as your usual medication, ask the pharmacist to double-check.
• Choose over-the-counter medications by their active ingredients, not by brand name. Drug manufacturers often use well-established brand names to launch a series of related—but different—products.
• Find out what the therapeutic effects and side effects of your medication are. Once you start taking the drug, be alert to any unforeseen effects, which could signal a mix-up.
• Maintain a complete list of all the drugs you take, prescription and over-the-counter, including dosages as well as brand and generic names. Update the list monthly, and bring it with you whenever you visit your doctor or drugstore.