Drugs used to treat common conditions like sleeplessness, allergy and bladder control could have an adverse effect on the memory of people who use them, says a study conducted by researchers in the United States.

Researchers also link this class of medications called anticholinergic drugs to the increased risk of mental decline among elderly patients. Anticholinergic drugs block the activity of acetylcholine, a chemical that carries signals between nerve cells.

Drugs belonging to this class are used treat many medical conditions including nausea, allergies, stomach and bowel problems, depression, epilepsy and Parkinson's disease.

Researchers conducted a long-term study tracking anticholinergic use among 1,652 African-American men and women over age 70. The study recorded details of all medicines the participants consumed and tested their mental abilities to make sure that nothing was amiss.

The same series of tests were repeated after three and six years and details related to memory, language and attention span was carefully noted down and analyzed. It was found those who regularly took one anticholinergic drug showed significantly more decline in their mental faculties after six years.

And patients who regularly took two anticholinergic drugs seemed to double the risk of memory loss over the research period. The report, published in Neurology, a medical journal owned by the American Academy of Neurology, further indicated that patients taking anticholinergic drugs were 46 percent more likely to depict some decline in their mental faculties.

Having said so, the researchers wrote that these mental declines were fairly mild and that the research also did not establish a link between anticholinergic drugs and a higher risk of Alzheimer's and other types of dementia.

Anticholinergic drugs are also used largely for problems related to urinary bladder-control and sleeplessness among older patients. Diphenhydramine, an anticholinergic, is widely used to treat sleeplessness while Darifenacin flavoxate and oxybutynin are among the anticholinergic drugs prescribed to manage bladder control.

Temporary disorientation, memory loss and confusion due to short-term impairment of mental function are among the known adverse reactions of anticholinergic drugs. These reactions usually occur with higher dosages though there is no clear evidence of possible side-effects on the brain when used long term.

The research has been funded by grants from the US National Institutes of Health and the Alzheimer's disease and Related Disorders Association. The team now plans to study whether the mental decline they noted with anticholinergic use might be reversible.