About four per cent of Americans aged 57 or older are potentially at risk of having a major drug interaction, including after taking over-the-counter supplements such as gingko with Aspirin, a study suggests.

In Wednesday's Journal of the American Medical Association, researchers said more than half of adults in the U.S. from ages 57 to 85 were using five or more prescription or non-prescription drugs, and one in 25 was taking potentially dangerous combinations.

"Patients need to know that while medications are often beneficial, they're not always safe," said lead author Dima Qato, a University of Chicago pharmacist.

"If they need to self-medicate with over-the-counter or dietary supplements, they should definitely consult with their physicians or pharmacists."

The researchers interviewed 2,976 people between June 2005 and March 2006 about which medications they routinely used.

During the study period, 91 per cent of older adults regularly used at least one medication, which translates to more than 50 million people.

Participants weren't asked if they had a bad reaction to drug combinations, and researchers did not assess whether the medications were taken inappropriately.

But a recent report estimated adults over 65 make up more than 175,000 emergency department visits a year in the U.S. for adverse drug reactions, and commonly prescribed drugs accounted for a third of these visits, said study co-author Dr. Stacy Tessler Lindau of the University of Chicago Medical Center in Illinois.

Excess bleeding reactions

Nearly half of the potential interactions between drugs could cause bleeding problems, the researchers found.

The blood thinner warfarin, sold under the brand name Coumadin, was the most common example involved in potentially dangerous combinations.

Wafarin was often taken together with Aspirin, which can be used to prevent heart attacks. Both warfarin and Aspirin increase the risk of bleeding when taken individually, and more so when taken taken together. Taking warfarin together with garlic pills is also riskier, the researchers said.

Signs of bleeding problems include bruising easily, bleeding from the gums or cuts that is hard to stop, and blood in the urine.

Other common and risky combinations the researchers found were:

• Lisinopril, a blood pressure drug, taken with potassium, which combined can cause abnormal heart rhythms. Potassium is often prescribed to restore low levels of this mineral caused by certain blood pressure drugs.
• Prescription cholesterol drugs called statins taken with over-the-counter niacin, a type of vitamin B that also lowers cholesterol. This combination increases risks for muscle damage.

Careful monitoring needed

The researchers recommended that patients carry a list of all the drugs and supplements they are taking in their wallet or purse.

They also suggested that doctors, pharmacists and other health professionals remember to ask patients about all the medications they are using.

When taking multiple medications, it's a good idea to keep in close contact with a doctor, suggested Dr. Jerry Gurwitz, chief of the geriatric medicine division at University of Massachusetts Medical School.

"There are definitely many instances where if they're monitored carefully and there's good reason for using them, that they could be used safely," said Gurwitz, who wasn't involved in the study.

The Institute for Safe Medication Practices' new website, consumermedsafety.org, allows people to enter the names of medications to check for potentially dangerous interactions.

With files from Associated Press, Reuters