Scientists have developed a once-a-day pill that they hope could potentially cure Alzheimer's disease.
The drug cuts build up of a key protein
Tests in mice have shown the drug, PBT2, prevents build up of the amyloid protein linked to the disease.
Protein levels dropped by 60% within 24 hours of a single dose, and memory performance improved within five days.
A team from Australia's Mental Health Research Institute of Victoria, who are behind the research, hope the drug could be on the market in four years.
Human tests are due to start next month, followed by a major international trial next year.
Already preliminary tests in humans have showed the drug does not cause any major side-effects.
The researchers believe the drug has the potential to delay the onset of disease, or slow down its progression.
Alzheimer's is a progressive and fatal brain disease. It is the most common cause of dementia and affects around 450,000 people in Britain.
It is linked to the build up of deposits of amyloid protein - called Abeta - in the brain, which form plaques often seen in the brains of Alzheimer's patients at post mortem.
The Australian researchers showed that PBT2 therapy quickly and significantly improved spatial memory in mice.
They used a water-maze test which involved the mice remembering the location of a submerged platform in order to navigate the maze.
Lead researcher Professor Ashley Bush said: "This data is compelling and very exciting because it shows that PBT2 not only may facilitate the clearance of Abeta from the brain or prevent its production, but more importantly may improve cognition."
His colleague Professor George Fink, head of the Mental Health Research Institute, described the research as a major breakthrough.
"Though much depends on the next phase of human clinical trials, early results indicate this drug offers hope to people with Alzheimer's disease."
Dr Susanne Sorenson, head of research at the Alzheimer's Society, said: "Initial tests have shown that the drug improves cognition and memory in mice, and we hope the same results can be recreated in humans."
However she added: "These findings are still relatively new and many more tests and studies are now needed to prove the concept will work in people with Alzheimer's disease and ensure the best treatments for this condition are made available as quickly as possible."
Dr Sorenson said the results of the PBT2 study were one of many encouraging discoveries presented at last week's International Convention for Alzheimer's Disease which showed positive steps were being made towards finding new and better treatments.
Rebecca Wood, chief executive of the Alzheimer's Research Trust, said PBT2 was related to Clioquinol, an ointment used to treat skin infections such as athlete's foot.
She said "Scientists still have a lot of work to do before a drug could be available for patients.
"Much more research is needed even to see whether preventing the amyloid build-up is really a true benefit for patients.
"It would also be necessary to develop a drug that reduced the amyloid without removing it entirely, since a healthy brain still needs amyloid."