Millions of people who use non-steroidal anti-inflammatory drugs (NSAIDs), such as naproxen and ibuprofen, shouldn't bank on the drugs helping them ward off dementia.

A study in this week's Neurology suggests that NSAID users do not have lower rates of dementia and that increased use of the pain relievers may actually raise the risk of cognitive decline.

"We had high hopes that these non-steroidal arthritis drugs might play a role, in part because other studies had been promising," says study author Eric Larson, executive director of Group Health Center for Health Studies, a Seattle-based HMO.

Researchers followed 2,736 members of Group Health who were an average age of 75 at the study's start. Participants were tracked for 12 years to see if they developed dementia, including Alzheimer's disease. Participants' pharmacy records were evaluated for use of prescription and over-the-counter pain relievers, and they were questioned about their NSAID use as well.

Results showed 351 people had a history of heavy NSAID use at the study's start, while 107 people became heavy users during the follow-up period. Heavy users took at least one NSAID a day for at least 16 months of a two-year period.

During the study, 476 people developed dementia, and heavy NSAID users had a 66% higher risk of developing the condition than those with low or no use.

Larson says he was surprised at the outcome because inflammation is thought to play a role in dementia and because other studies suggested anti-inflammatory pills lowered dementia risk.

"We have years and years of drug exposure data that was extremely accurate. We did not expect these findings," Larson says.

Duke aging expert Murali Doraiswamy says that the latest results aren't a revelation to him and that previous trials evaluating Vioxx, aspirin and prednisone, among other anti-inflammatory medications, did not show reduced risks cognitive decline. "Any benefits noted in prior studies were likely due to an epiphenomenon — the people taking NSAIDS were younger, healthier and better educated, all of which biased the results."

The study doesn't disprove the theory that inflammation is a factor in Alzheimer's, though, says Jason Karlawish, associate director of the Penn Memory Center at the University of Pennsylvania. "Negative studies like this that fail to prove the hypothesis leave thousands of questions to be answered," Karlawish says.

The new data highlight the need for early detection and better biomarkers, says Alzheimer's Association vice president Bill Thies. "If you could tell who's going to need dementia drugs at age 40 and study them, you may have a totally different result."