Scientists believe they could be on the cusp of a breakthrough, after a drugs company said it had the first treatment of its kind for Alzheimer's.
The drug, which is called aducanumab, cannot cure it but Biogen says it slows down the rate at which it progresses, essentially meaning people stay more like themselves for longer.
This came as a surprise as the company had suspended the drug trial in March 2019 because of disappointing results.
But now a larger dataset has been analysed and Biogen says it shows that higher doses of aducanumab can provide a significant benefit to patients with early Alzheimer's.
The BBC has been to University College London to find out how the drug works.