The UK’s drugs regulator – the MHRA – has approved the Alzheimer’s drug donanemab, but it won’t be available on the NHS.

The National Institute for Health and Care Excellence (Nice), which determines what treatments are available on the NHS, decided not to recommend donanemab for NHS use. This is because of its cost, potential side-effects and what some consider insufficient benefits.

While Nice’s decision is disappointing for a lot of people (about 70,000 people people in England would have qualified to receive the drug), it’s important to know why the decision was made.

A key characteristic of Alzheimer’s disease is the presence of amyloid plaques. These are sticky proteins that clump together and destroy brain cells (neurons), resulting in Alzheimer’s.

Donanemab is a monoclonal antibody – a lab-made protein that targets and binds to amyloid to help eliminate it. This treatment is administered by an intravenous infusion, so the drug is delivered directly into the bloodstream. Each session lasts about 30 minutes and is needed every four weeks.

In a clinical trial, donanemab was shown to be reasonably successful. The trial compared participants with early........

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