THURSDAY, April 17 (HealthDay News) -- Common medications known as anticholinergic drugs -- used to treat ulcers, stomach cramps, motion sickness, Parkinson's disease and urinary incontinence -- may cause older people to lose their thinking skills more quickly than seniors who don't take the medicines, new research suggests.

"What we found is being on these drugs does worsen your cognitive performance," said Dr. Jack Tsao, an associate professor of neurology at Uniformed Services University in Bethesda, Md., who led the study of the effect of the medications on older adults who were, on average, 75. "In the course of a few years, there is a small slippage. It's a minor effect."

Medications for bladder problems and Parkinson's appear to have the worst effect on memory, he said.

Anticholinergic drugs are a class of medicines that work by blocking the binding of a brain chemical called acetylcholine to its receptor in nerve cells.

"You need acetylcholine for [good] memory," Tsao explained. Drugs used to treat Alzheimer's inhibit the enzyme which breaks down acetylcholine, he said, allowing more of it to be used by the brain.

Tsao was expected to present his research Thursday at the American Academy of Neurology annual meeting, in Chicago.

Tsao's study adds to the body of evidence on the effect of these drugs on memory. "We've known for a long time that in people with Alzheimer's disease, if you put them on drugs with anticholinergic activity, it clearly worsens their memory, without a doubt."

In the new study, he said, they looked at people who had normal cognitive function.

"Taking the drugs doesn't increase your risk of getting Alzheimer's. There was no change in the progression overall to the diagnosis of Alzheimer's," Tsao stressed. However, there was a decline in cognitive abilities.

Tsao's group evaluated the annual changes in thinking ability of 870 Catholic nuns and clergy members who are part of an ongoing study of older people called the Rush Religious Orders Study.

During the eight-year follow-up, 679 participants took at least one medicine that was an anticholinergic. Those who took the drugs had a rate of cognitive function decline that was 1.5 times faster than those not on the drugs.

Overall, those not on the drugs had a decline in cognitive performance of about 0.5 on the scale used, Tsao said. Those on the medicines showed a decline of 1.5.

When they looked more closely at individual drugs, they found those used for bladder problems and Parkinson's disease impaired memory about three times as much as those not taking anticholinergic drugs.

Another study, published in 2006 in the British Medical Journal, found that elderly people taking anticholinergics had poorer performance on memory and other tests than those who didn't take the drugs.

Another expert, Dr. Niall Galloway, a urologist and director of the Emory University Continence Center in Atlanta, said one strength of the study is that it includes relatively large numbers. Overall, however, he said, "this is not a strong study."

One major problem, he said is that the volunteers are "lumped together," regardless of what the indication is for taking an anticholinergic. It would be helpful to know more specific information, such as how many anticholinergics each patient was taking and how those taking one compared to those taking more than one.

Tsao agreed that more specific information would be better. Meanwhile, he said, "my recommendation is, if someone is having what they feel is a noticeable problem with their ability to remember things, they need to go see their doctor. And they need to mention if they are on one of these drugs."

Galloway agreed, saying that many patients may stay on medications longer than they need to, either because they forget to ask the doctor about it or the doctor doesn't re-evaluate. It's a fair question, he said, to ask your doctor if you need to continue a medication.

More information

To learn more about older adults and medications, visit the U.S. National Institute on Aging.