Experts have hailed the “beginning of the end” in the search for effective Alzheimer’s treatments after a new drug reduced memory decline among patients with early stages of the disease.

Lecanemab, which is designed to target and clear amyloid – one of the proteins that builds up in the brains of people with Alzheimer’s – was found to slow decline in patients’ memory and thinking.

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 initial results in September from a trial on 1,795 participants with early Alzheimer’s disease.

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

READ MORE: Why we are at a 'historic moment' in Alzheimer's research

Full results from the study have since been published in The New England Journal of Medicine, with experts hailing it as long-awaited proof that Alzheimer’s disease can be treated.

“This trial is an important first step, and I truly believe it represents the beginning of the end,” said Professor John Hardy, group leader at the UK Dementia Research Institute at University College London.

“The amyloid theory has been around for 30 years so this has been a long time coming. It’s fantastic to receive this confirmation that we’ve been on the right track all along, as these results convincingly demonstrate, for the first time, the link between removing amyloid and slowing the progress of Alzheimer’s disease.

“The first step is the hardest, and we now know exactly what we need to do to develop effective drugs. It’s exciting to think that future work will build on this, and we will soon have life-changing treatments to tackle this disease.”

Prof Bart De Strooper, director at the institute, added: “The overall conclusion is extremely positive. This trial proves that Alzheimer’s disease can be treated.”

Prof Nick Fox, director of the Dementia Research Centre, said: “I believe, it confirms a new era of disease modification for Alzheimer’s disease.

“An era that comes after more that 20 years of hard work on anti-amyloid immunotherapies – by many many people – and many disappointments along the way.”

Dr Richard Oakley, associate director of research at Alzheimer’s Society, said the results had the potential to be “game-changing”.

“They give us hope that in the future people with early Alzheimer’s disease could have more time with their loved ones,” he said.

However, experts warned that UK officials have much to do to prepare to deliver the drug, provided it gets regulatory approval.

There are two ways to tell whether there is amyloid on the brain – a brain scan or biomarker test which is currently done through lumbar puncture.

Professor Bart De Strooper new roleProfessor Bart De Strooper (Medical Research Council/PA)

While a blood test is on the horizon, dementia services must rely on current tests which are expensive and can have big waiting lists.

Private patients and those living near to big dementia services can access these diagnostic tests, but the vast majority of the public cannot, experts said.

READ MORE: Alzheimer's Disease Aberdeen trial could spark early diagnosis breakthrough

They warned that unless there are big changes in diagnostic services, people could become ineligible for lecanemab treatment while on the waiting list for diagnosis because it can only be given to patients with mild disease – if their disease progresses to a moderate stage while on the waiting list, they will no longer be eligible for treatment.

Prof De Strooper said: “The participants of this trial were all people with very early-stage Alzheimer’s disease, which raises the question of how we ensure that people can access these drugs at the right stage in their disease course.

“In parallel, we must focus on making early diagnosis easier and more accessible, so that treatments can be administered when they are most likely to have a positive impact, before amyloid levels are too high and start to cause damage to the brain.”

Experts also stressed that more work still needed to be done to investigate the drug’s side effects.

“The trial results have shown us that there is a risk of side effects, including brain bleeds in a small number of cases,” Prof Hardy said.

“This doesn’t mean the drug can’t be administered, but that will be important to have rigorous safety monitoring in place for people receiving lecanemab, and further trials to fully understand and mitigate this risk.”

*Remember we are currently running our best Herald subscription offer to date in a special Black Friday deal. Full details here.