It comes weeks after the EU’s drugs regulator also rejected the drug, saying the risk of serious brain swelling did not outweigh its small impact on slowing cognitive decline. It also said the effects of the drug on delaying cognitive decline were small.

The Nice decision is a further blow to the companies behind the drug, Eisai and Biogen, as the treatment faces slow take-up in the US. It also lays bare the complexities tied to a new class of drugs that have benefited early-stage patients, but can cause serious side-effects.