"Our message is to be careful when using these medicines," said U.S. Navy neurologist Dr. Jack Tsao, who led the study. "It may be better to use diapers and be able to think clearly than the other way around."
Urinary incontinence sometimes can be resolved with non-drug treatments, he added, so patients should ask about alternatives. Exercises, biofeedback and keeping to a schedule of bathroom breaks work for many.
U.S. sales of prescription drugs to treat urinary problems topped $3 billion in 2007, according to IMS Health, which tracks drug sales. Bladder control trouble affects about one in 10 people age 65 and older, according to the National Institute on Aging, which helped fund the study. Women are more likely to be affected than men. Causes include nerve damage, loss of muscle tone or, in men, enlarged prostate.
The research began after Tsao met a 73-year-old patient. Shortly after starting an incontinence drug, she began hallucinating conversations with dead relatives and having memory problems. Her thinking improved when she stopped the drug for several months.
Tsao and his colleagues knew of similar reports. They decided to look at a large group of people to see if they could measure an effect of these and other medications that affect acetylcholine, a chemical messenger that shuttles signals through the brain and the rest of the nervous system. The drugs block some nerve impulses, such as spasms of the bladder.
The findings, released Thursday at a meeting of the American Academy of Neurology, come from an analysis of the medication use and cognitive test scores of 870 older Catholic priests, nuns and brothers who participated in the Religious Orders Study at Chicago's Rush University Medical Center. The average age was 75.
Researchers tracked them for nearly eight years, testing yearly for cognitive decline. They asked them to recite strings of numbers backward and forward, to name as many different kinds of fruit as they could in one minute and to complete other challenges during the annual testing.
Nearly 80 percent of the study participants took one or more of a class of drugs called anticholinergics, including drugs for high blood pressure, asthma, Parkinson's disease and incontinence drugs such as Detrol and Ditropan.
The people who took the drugs had a 50 percent faster rate of cognitive decline compared to those who didn't take any. The researchers considered other risk factors for memory loss, such as age, and still found the link. The researchers found no increased risk for the memory-robbing disorder Alzheimer's in people taking the drugs.
The incontinence drugs were among the most potent and were the most frequently taken of all the anticholinergics in the study. That's why the researchers believe they are driving the memory problems, Tsao said.
Some experts said the research supports previous observations and is helpful because it measures the size of the effect.
"This paper adds important new data to the picture," said Dr. Elaine Perry of Newcastle University in England, who has done similar research but was not involved in the new study.
More research is needed on the effects of anticholinergic drugs on memory, Tsao said. Doctors should do baseline cognitive testing on patients before prescribing the drugs, he recommended.
A representative of Pfizer Inc., maker of the top-selling Detrol, said patients should always talk to their doctors about problems while taking medication.
"Detrol has been on the market since 1998. It has been prescribed more than 100 million times worldwide," said Ponni Subbiah, Pfizer's vice president of medical affairs, in an e-mail response to questions.
Confusion and memory impairment were added to prescribing information for Detrol in 2006, Subbiah said, after some patients reported the problems. Since the reports weren't part of a medical study, "the frequency of events and the role of Detrol in their causation cannot be reliably determined," he said.