WEDNESDAY, March 7 (HealthDay News) -- A new study offers up mixed results about two medications used to treat the symptoms of the memory-robbing disease known as Alzheimer's.

While patients didn't get a major mental boost when doctors added the drug Namenda to their regimen when they were already taking Aricept, they did find that continuing Aricept -- a commonly prescribed drug for Alzheimer's in the United States -- seemed to help.

The results, which appear in the March 8 issue of the New England Journal of Medicine, may seem a bit murky, especially because it's difficult to measure the effects of the drugs on day-to-day living. However, study author Dr. Robert Howard, a professor of old age psychiatry and psychopathology at the Institute of Psychiatry at King's College London, said both drugs are worth taking, possibly even together.

"While these drugs will not stop or slow down the tragic course of Alzheimer's disease, they can continue to improve symptoms as the disease becomes more severe," Howard said. "If you can, try to stay on them. The benefits are tangible and, if anything, seem to get larger as the illness progresses."

While Alzheimer's disease is incurable, several drugs are available to treat symptoms such as memory loss in patients with mild to moderate forms of the illness. It's not clear, however, what happens as the disease worsens.

In the new study, British researchers assigned 295 Alzheimer's patients with moderate to severe disease to one of four groups. All had been on the drug Aricept (donepezil). The patients either continued the drug; stopped the drug; stopped it and started Namenda (memantine); or they continued taking Aricept and started taking Namenda, too.

The study, which lasted for a year, was funded by the U.K. Medical Research Council and the U.K. Alzheimer's Society.

Patients who continued on Aricept had less impairment than those who didn't; the improvement was equal to about three to four months of decline, Howard said. "That's a noticeable difference for patients, caregivers and their doctors."

However, there didn't seem to be any significant benefit to taking both drugs. That contradicted a previous study that found there was a benefit, said Dr. Lon Schneider, a professor of psychiatry, neurology and gerontology at the University of Southern California Keck School of Medicine, who wrote a commentary accompanying the study.

Aricept can be a difficult drug to tolerate. About half of those who take it will quit due to side effects, Schneider explained. Those side effects include anorexia, weight loss, heart trouble and agitation.

The findings could be interpreted in various ways, Schneider noted. The study provides evidence to support continuing Aricept, he said, and suggests that it may not be not necessary to start Namenda.

Schneider said he doubts the research would have a major impact by decreasing how often the drugs are prescribed. Still, the findings allow people to understand how much of an effect patients might encounter if they go off Aricept, he noted.

More information

For more about Alzheimer's disease, visit the U.S. National Library of Medicine.