Methylene blue was previously used as a cure for malaria, but was disliked by patients as it had the side-effect of turning urine blue.

The drug has since been used to treat other conditions, but there have been concerns over damage to brain tissue.

But a new research effort is looking at methylene blue in very small doses, which should avoid the neurotoxic effects of larger doses.

Tests in the lab show that it slows cellular ageing and enhances mitochondrial function -- spurring hopes that it could be used to treat degenerative brain conditions.

"The results are very encouraging," said Dr Hani Atamna of the Children's Hospital & Research Center in Oakland, California.

"We'd eventually like to try to prevent the physical and cognitive decline associated with ageing, with a focus on people with Alzheimer's disease."

"One of the key aspects of Alzheimer's disease is mitochondrial dysfunction, specifically complex IV dysfunction, which methylene blue improves."

"Our findings indicate that methylene blue, by enhancing mitochondrial function, expands the mitochondrial reserve of the brain."

"Adequate mitochondrial reserve is essential for preventing age-related disorders such as Alzheimer's disease."

One of Dr Atamna's colleagues is excited about the prospect of treating serious diseases with a drug that is very cheap to manufacture.

"What we potentially have is a wonder drug." said Dr Bruce Ames.

"To find that such a common and inexpensive drug can be used to increase and prolong the quality of life by treating such serious diseases is truly exciting."