A dementia charity has hailed a “historic moment” in Alzheimer’s research as a new drug has been found to reduce memory decline among patients with early-stage disease.

Lecanemab was found to slow decline in participants’ memory and thinking.

Alzheimer’s Research UK said the finding was a “historic moment for dementia research”, as this is the first later-stage trial of an Alzheimer’s drug “in a generation” to successfully slow cognitive decline.

The phase three clinical trial results have been reported by Eisai, a Tokyo-based pharmaceutical company that has partnered with US biotech firm Biogen to develop lecanemab.

Eisai reported results from a trial on 1,795 participants with early Alzheimer’s disease.

Lecanemab is designed to target and clear amyloid, one of the proteins that builds up in the brains of people with Alzheimer’s at an early stage of the disease.

Eisai examined the drug – an “anti-amyloid beta protofibril antibody” – for the treatment of mild cognitive impairment for patients with amyloid in the brain.

The pharmaceutical company reported “highly statistically significant” results.

It compared results of people taking the drug and those taking a placebo – or dummy drug.

Scientists found that after 18 months the drug slowed the disease progression by 27% compared with those taking the placebo.

Findings were evident as early as six months after participants started taking the drug.

The company also reported differences in the build-up of amyloid in the brain in scans of participants, with those taking the drug having lower levels compared to those taking the placebo.

“Alzheimer’s disease not only presents a great challenge for patients and their families, but it also negatively impacts society, including decreased productivity, increased social costs and disease-related anxiety,” Haruo Naito, chief executive of Eisai, said.

“We believe that helping to alleviate these burdens will positively impact society as a whole.”

More detail on the study will be presented to the Clinical Trials On Alzheimer’s Congress in November.

Eisai said it plans to discuss the results with medical regulators with a view to file for market approval before the end of March.

Commenting on the findings, Dr Susan Kohlhaas, director of research at Alzheimer’s Research UK, said: “This is a historic moment for dementia research, as this is the first phase three trial of an Alzheimer’s drug in a generation to successfully slow cognitive decline.

“These results show that lecanemab slows the progression of memory and thinking problems in people with early Alzheimer’s, demonstrating a major breakthrough in dementia research.

“This is the first drug that’s been shown to not only remove the build-up of a protein called amyloid in the brain, but to have a small but statistically significant impact on cognitive decline in people with early-stage disease.

“The drug can also cause substantial side effects which will need to be considered.

“These top-line results, announced by the pharmaceutical company that make the drug, Eisai, offer new hope to people affected by this cruel and devastating disease.

“Before a drug is made available, regulators in different parts of the world, including the UK, will still need to assess the full data to determine whether lecanemab is safe and effective enough to be used in people with Alzheimer’s.

“If the drug is approved, it is essential that it gets to the people who may benefit from it as quickly as possible.

“Today’s results were only possible because of the volunteers who took part in this trial, previous studies of this drug and wider dementia research across the world.

“This drug has only been tested for people in the early stages of Alzheimer’s and won’t be a silver bullet for all causes of dementia.

“We hope today’s news will spark renewed investment in dementia research across the globe and political leadership to deliver the funding and infrastructure needed to make life-changing new treatments a reality.”

Of the people who experienced side effects, the most common were headaches and swelling in the brain known as “amyloid-related imaging abnormalities”.

Dr Richard Oakley, associate director of research at Alzheimer’s Society, added: “This research could be game-changing in the treatment of Alzheimer’s disease.

“For decades, people with Alzheimer’s disease have been desperately waiting for a drug to slow down the progress of the disease, so this exciting news represents a real breakthrough moment in dementia research.”

Commenting on the study, Dr Catherine Mummery, consultant neurologist at the National Hospital for Neurology and Neurosurgery, said the results are “exciting” adding: “If borne out by the full details of the study, as they are the clearest indicator so far that by lowering amyloid levels in the brain, cognitive decline can be slowed.

“The results are consistent in size with those found in earlier phase trials with other anti-amyloid drugs, and with the positive, controversial trial in aducanumab. This convergence strengthens the findings. However, the size of the effect, while significant, is small – the disease is slowed by 27% over 18 months. What we cannot know yet is whether that effect increases over time in an individual; that would be predicted but is untested – time will tell.”

Rob Howard, professor of old age psychiatry, University College London, added: “This is an unambiguously statistically positive result and represents something of an historic moment when we see the first convincing modification of Alzheimer’s disease.

“God knows, we’ve waited long enough for this.”

Dr Liz Coulthard, associate professor in dementia neurology at the University of Bristol, added: “This is a gold standard study in people with fairly early signs of Alzheimer’s disease.

“Although not curative, lecanemab slowed decline in day-to-day function compared to placebo. So lecanemab potentially offers prolonged good quality life in people with early signs of Alzheimer’s disease.

“Up to now, many people have not come forward when they first worry about their memory as there were no treatments for dementia.

“It is very likely more people will come to see their doctor now – and we, as doctors, need to be ready. Most people with mild memory symptoms will not have Alzheimer’s disease. We need to develop an effective and quick triage system so we can reassure people without Alzheimer’s and offer treatment to those with Alzheimer’s.

“Our health system moved impressively rapidly to deliver trials and therapies for Covid. Let’s hope we can apply the same efficiency for people with Alzheimer’s disease.”