(CNN) — The US Food and Drug Administration granted accelerated approval Friday for the Alzheimer's disease drug lecanemab, one of the first experimental dementia drugs to appear to slow the progression of cognitive decline.

"Alzheimer's disease immeasurably incapacitates the lives of those who suffer from it and has devastating effects on their loved ones," Dr. Billy Dunn, director of the Office of Neuroscience in the FDA's Center for Drug Evaluation and Research, said in a statement. "This treatment option is the latest therapy to target and affect the underlying disease process of Alzheimer's, instead of only treating the symptoms of the disease."

Lecanemab will be marketed as Leqembi, the FDA statement said. It has shown "potential" as an Alzheimer's disease treatment by appearing to slow progression, according to Phase 3 trial results, but it has raised safety concerns due to its association with certain serious adverse events, including brain swelling and bleeding.

In July, the FDA accepted Eisai's Biologics License Application for lecanemab under the accelerated approval pathway and granted the drug priority review, according to the company. The accelerated approval program allows for earlier approval of medications that treat serious conditions and "fill an unmet medical need" while the drugs continue to be studied in larger and longer trials.

If those trials confirm that the drug provides a clinical benefit, the FDA could grant traditional approval. But if the confirmatory trial does not show benefit, the FDA has the regulatory procedures that could lead to taking the drug off the market.

What is known about lecanemab

Lecanemab, a monoclonal antibody, is not a cure but works by binding to amyloid beta, a hallmark of Alzheimer's disease. In late November, results from an 18-month Phase 3 clinical trial published in The New England Journal of Medicine showed that lecanemab "reduced markers of amyloid in early Alzheimer's disease and resulted in moderately less decline on measures of cognition and function than placebo at 18 months but was associated with adverse events."

The results also showed that about 6.9 percent of the trial participants given lecanemab, as an intravenous infusion, discontinued the trial due to adverse events, compared with 2.9 percent of those given a placebo. Overall, there were serious adverse events in 14 percent of the lecanemab group and 11.3 percent of the placebo group.

The most common adverse events in the lecanemab group were reactions to the intravenous infusions and abnormalities on their MRIs, such as brain swelling and bleeding called amyloid-related imaging abnormalities, or ARIA, which can become life-threatening.

Some people who get ARIA may not have symptoms, but it can occasionally lead to hospitalization or lasting impairment. And the frequency of ARIA appeared to be higher in people who had a gene called APOE4, which can raise the risk of Alzheimer's disease or other dementias. ARIA "were numerically less common" among APOE4 noncarriers, the study showed.

The drug's prescribing information carries a warning about ARIA, the FDA says.

The trial results also showed that about 0.7 percent of participants in the lecanemab group and 0.8 percent of those in the placebo group died, corresponding to six deaths in the lecanemab group and seven in the placebo group.

Leading up to the FDA decision, some advocacy groups, including the Alzheimer's Association, were pushing for accelerated approval of lecanemab.

"We believe, based on the totality of positive data from clinical trials of this treatment, that the FDA should approve. Peer-reviewed, published results show lecanemab will provide patients in the earliest stages of Alzheimer's more time to participate in daily life and live independently. It could mean many months more of recognizing their spouse, children and grandchildren," Maria Carrillo, the group's chief science officer, said in a statement days before the FDA decision.

She added that the Alzheimer's Association hopes that the Centers for Medicare and Medicaid Services "will move quickly" to cover the drug and "revise its coverage decision that currently blocks access to this treatment." CMS determines whether to cover FDA-approved therapies based on whether it deems them to be safe and effective. Carrillo said that the Alzheimer's Association "has filed a formal request asking CMS to provide full and unrestricted coverage for FDA-approved Alzheimer's treatments."

In 2021, the FDA approved the drug Aduhelm for early phases of Alzheimer's disease — but that FDA decision has been shrouded in controversy as a congressional investigation found last week that the FDA's "atypical collaboration" to approve the high-priced Alzheimer's drug was "rife with irregularities."

Before Aduhelm, the FDA had not approved a novel therapy for the condition since 2003.

More than 6.5 million people in the United States live with Alzheimer's disease, according to the Alzheimer's Association, and that number is expected to grow to 13.8 million by 2060.

'This drug is not for everyone'

The FDA's accelerated approval was expected, said Dr. Richard Isaacson, director of the Alzheimer's Prevention Clinic in the Center for Brain Health at Florida Atlantic University's Schmidt College of Medicine.

Isaacson said lecanemab can be "another tool" in his toolbox to fight Alzheimer's disease.

"I will prescribe this drug in the right person, at the right dose and in a very carefully monitored way, but this drug is not for everyone," he said.

"I would do genetic testing for APOE4 first. I would have a frank discussion with my patients," he said. "If someone is having side effects, if someone is on a blood-thinning medication, if someone has a problem, they need to discuss this with the treating physician, and they need to seek medical attention immediately."

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