An allergy drug used in Russia in the 1980s is showing new promise in the treatment of Alzheimer's disease, researchers say.

A study conducted in Russia found that Alzheimer's patients who took the drug Dimebon had significant improvement in thought processes over a 12-month period compared to patients who were given a placebo.

The researchers said that this is the first drug to yield year-long improvement in those with Alzheimer's.

"In this study, Dimebon improved the clinical course of Alzheimer's disease, which is important given that the natural course is progressive deterioration over time," lead study author, Dr. Rachelle Doody of the Baylor College of Medicine in Houston, Tex., said in a statement.

"The results of this trial suggest that, if the findings are replicated, Dimebon could advance Alzheimer's treatment, offering more hope for patients and their caregivers."

The findings are published in the journal The Lancet.

Researchers monitored thinking and memory ability, overall function, psychiatric and behavioural symptoms and the ability to perform daily activities in 183 patients.

The researchers found improvement in all of these aspects of the patients' lives.

The scientists believe that Dimebon works by stabilizing mitochondria, the parts of cells that produce energy. They also think that the drug slows or inhibits the death of brain cells.

The findings do have some drawbacks. For one, Dimebon is not widely available outside of Russia, and is not available in Canada.

As well, the study needs to be replicated in a larger, long-term trial before the drug can really be deemed both safe and effective, Dr. Jack Diamond of the Alzheimer Society of Canada told CTV News.

Doody did say that the next phase of this study will expand the participant pool to include several international locations, including the United States.

Alzheimer's disease is a progressive, neurodegenerative disease that destroys brain cells and leads to a decline in memory, judgement, language and behaviour. It is the most common form of dementia.

According to the Alzheimer Society of Canada, about 300,000 Canadians over age 65 have the disease.