“This is a new and emerging area of ​​medicine that will no doubt develop rapidly,” said Samantha Roberts, chief executive of NICE, in a statement. “But the reality is that the benefits of this first treatment are simply too small to justify the significant cost to the NHS. It is an intensive treatment for patients, requiring a two-weekly hospital visit with qualified staff to monitor for signs of serious side effects, plus the cost of purchasing the drug.”

NICE is now accepting public comments on the draft guidance until September 20 and will review it before making its final decision. In a statement, Eisai said it “remains committed to working with NICE to make lecanemab available to eligible patients via the NHS as soon as possible.”

Leqembi was approved in the United States last year and also received the green light in countries including Japan, China, South Korea and Israel. But last month, European Union regulators asked that the drug be rejected there, saying its benefits did not outweigh the risks associated with the treatment, which are sometimes dangerous.

Eisai and Biogen said they would appeal the European Medicines Agency’s decision.

Conflicting assessments by different regulatory and cost-effectiveness agencies have heightened the debate about the benefits, risks and costs of Leqembi. Leqembi is considered a drug that offers limited benefit against a devastating disease for which there are no other effective treatment options.

In the pivotal clinical trial, Leqembi only slightly slowed cognitive and functional decline in patients with early Alzheimer’s disease – by about 27 percent compared to placebo.

At the same time, treatments like Leqembi are complicated by concerns about side effects. These treatments aim to eliminate the amyloid protein plaques that litter patients’ brains and are a hallmark of the disease.

A major concern is a side effect called ARIA, brain swelling or bleeding that can be fatal in rare cases. In a clinical trial, 21 percent of patients receiving Leqembi experienced ARIA, although fewer than 3 percent of them had symptomatic cases. Two patients in an open-label extension of the trial died of severe brain bleeding after taking Leqembi. European regulatory authorities based their rejection of the drug on the risk of ARIA.

In its review, NICE said that while Leqembi could slow the progression of Alzheimer’s disease by up to six months, its “relatively small benefit” and associated costs meant it did not represent good value for money for the taxpayer. Leqembi must be administered twice a month in special infusion centres, and doctors must monitor patients for potentially dangerous ARIA events.

Overall, NICE calculated the costs associated with Leqembi, including infusions, monitoring and diagnostics, at almost $25,000.

“It is unfortunate and very disappointing that we are not there yet,” Jonathan Benger, chief medical officer at NICE, told reporters, but added: “The benefit of this drug is very small and the cost is very high.”

According to NICE, an estimated 70,000 people in England would have been eligible for Leqembi.

The Medicines and Healthcare Products Regulatory Agency approved Leqembi on Thursday independently of the NICE decision. The drug was specifically approved for patients with early-stage Alzheimer’s who have one or no copies of a genetic variant called APOE4. People with two copies of the gene are at higher risk of ARIA.

Because the agency licenses the drug, it is possible that people in the UK could try to obtain Leqembi through the private system and pay for it themselves.

Alzheimer’s advocacy groups and researchers described Thursday’s announcements as bittersweet, pointing to the historic approval of an at least moderately effective Alzheimer’s drug, but acknowledging that the NICE decision will leave the drug unaffordable for many patients.

This summer, the US approved another Alzheimer’s drug: Eli Lilly’s donanemab. Like Leqembi, it is an infusion to remove amyloid, which can trigger ARIA. Experts in Europe warn that health authorities may raise the same concerns about donanemab, which could lead to it being available as another therapy in the US but not in European countries.

“There are similar issues around side effects, similar issues around the modest benefit that the drug offers,” David Thomas, head of policy at Alzheimer’s Research UK, told reporters about donanemab, adding that “the same hurdles will exist.”