The first drug to slow the destruction of the brain in Alzheimer's has been heralded as momentous.

The research breakthrough ends decades of failure and shows a new era of drugs to treat Alzheimer's - the most common form of dementia - is possible. 

 Yet the medicine, lecanemab, has only a small effect and its impact on people's daily lives is debated. 

 And the drug works in the early stages of the disease, so most would miss out without a revolution in spotting it.

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