But the British government likely will not be paying for it after an independent agency separately issued draft guidance concluding the benefits of Leqembi "cannot be considered good value for the taxpayer".
As well as the cost of the drug, providing Leqembi requires patients be hospitalised every two weeks to receive it and be closely monitored for side effects.
Experts also noted the lack of data regarding the long-term effectiveness of Leqembi, made by Japanese drug maker Eisai.
"The reality is that the benefits this first treatment provides are just too small to justify the significant cost," said Dr Samantha Robers, chief executive of the National Institute for Health and Care Excellence, or NICE.
The draft guidance issued by NICE will be open for public consultation and all responses will be considered at a second meeting later in 2024 before final advice is issued.
The agency estimated about 70,000 people in Briton might benefit from Leqembi.
The drug is still available to be prescribed if patients pay for it privately.
In the United States, it costs about $US26,000 ($A39,000) per patient a year.
Some experts said that while they understood patients and their families might be disappointed by the news, there was hope better drugs might be developed soon.
Hilary Evans-Newton, chief executive of Alzheimers Research UK, said Leqembi represented "the beginning of a sea change in how diseases like Alzheimer's will be treated in the future".
She said there were more than 160 trials under way testing more than 125 experimental treatments for Alzheimer's across the globe.
"Despite today's frustrating news, it really is a matter of when, not if, new treatments become available," she said in a statement.
The US Food and Drug Administration authorised Leqembi in July 2023, clearing the way for Medicare and other insurance plans to begin covering the treatment.
In July, the European Medicines Agency recommended Leqembi not be authorised across the EU, saying the drug's impact on slowing cognitive decline did not outweigh its serious side effects, including swelling and potential bleeding in the brain.
6°C