As seniors seek treatment for multiple chronic conditions, the medications individually intended to make them better may collectively be making them worse, and in some cases putting them at mortal risk, a new study shows.

Up to 12 percent of older Americans -- more than 4 million people -- are taking more than eight different drugs, virtually assuring them of a drug interaction.

These are among the key findings in a study by AdvancePCS, a prescription benefit management firm, conducted in conjunction with Brandeis University.

"Medications provide effective treatment and have dramatically improved both quality and longevity of life. But polyprescribing, the lack of coordination and communication among all the different physicians writing prescriptions for an individual patient, is resulting in dangerous and potentially fatal drug interactions," said Andrew Garling, M.D., senior vice president, chief medical officer for AdvancePCS.

Report Shows Overall Rise in Use of Prescription Drugs

The study showed that most seniors age 65 and older are being treated for an average of four or more chronic disease conditions over the course of a year.

The number of prescribing physicians increases with the number of diseases being treated, which means different doctors are prescribing medications without always knowing what else the patient is taking.

Other key findings of the report indicate a dramatic increase in prescription medication use over the past 15 to 20 years among seniors:

For individuals age 65 and older, the number of physician visits made annually has increased by 20 percent per person since 1985. The average number of medications prescribed per visit is two, which is an increase of 33 percent since the 1980s.

Two-thirds of all office visits result in one or more prescriptions and nearly one-fourth result in four or more prescriptions, either newly prescribed or refills.

"To effectively and safely prescribe medication to individuals with four to 12 conditions or more would require all the physicians to know exactly what the patient is already taking," said Garling. "This is a huge problem as elderly patients may have difficulty keeping track of all of this information and physicians would need to know all the possible drug interactions."

The report recommends a number of solutions to this growing problem:

Health plans and other organizations responsible for the health benefits of older Americans should develop programs to make sure all physicians are aware of every medication currently prescribed to a patient.