Arthritis patient Edith Manley of San Leandro, Calif., is exceedingly careful when mixing medication, and with good reason. Nearly three years ago, Manley's 39-year-old daughter, Megan Nelson, died unexpectedly during a visit to Manley's home. Nelson had back pain for several years and occasional bouts of depression. Although her medical conditions weren't fatal, mixing prescriptions apparently was. "She was taking antidepressants for her depression and painkillers for her back pain," recalls Manley. "Her primary cause of death was listed as an accidental drug overdose.”

Manley and Nelson's teenage son, Mike, still grieve. And Manley is determined to get the word out: Mixing medications can be deadly, especially for people with arthritis or older Americans, who often have more than one health condition that requires medication.

Multiple Meds = Increased Dangers

Oscar Gluck, MD, clinical professor of medicine at the University of Arizona School of Medicine and director of the Arizona Rheumatology Center in Phoenix, says most of his patients have several diseases. In addition to a rheumatic disease, the most common diseases his patients have are diabetes, hypertension or cardiovascular disease. Although people of any age can have multiple health problems, the greatest risk is among those 50 and older, he says. As people age, their propensity to develop other health problems – and the likelihood that they are mixing medication – increases.

A recent study of adults in the United States showed that more than 90 percent of people 65 or older use at least one medication per week. More than 40 percent use five or more medications, and 10 percent use 12 or more.

"It's not unusual to see people with arthritis taking a dozen drugs. And if they're taking that many, I can usually find three or four that have the potential to interact," says Don Miller, professor and chairman of pharmacy practice in the College of Pharmacy Practice at North Dakota State University and pharmacotherapy specialist at Veterans Administration Hospital in Fargo.

Obviously, the more drugs you need to take, the more likely you are to be taking two that don't mix. But even if you are young, relatively healthy and just occasionally take medications for other problems, such as a cold, headache or infection, you could be at risk for medication reactions – if you and your doctor aren't careful.