The U.S. Food and Drug Administration (FDA) approved Aduhelm (aducanumab) on Monday for the treatment of Alzheimer's, the first new medicine against the disease in almost two decades, disregarding warnings that the much-debated treatment hasn't been shown to help slow the brain-destroying disease.

Accelerated approval 

Aduhelm was approved through the accelerated approval pathway, which can be used for a drug for a serious or life-threatening illness that provides a meaningful therapeutic advantage over existing treatments, according to the FDA.

The approval was based on study results showing it seemed "reasonably likely" to benefit Alzheimer's patients, the FDA said. 

The new drug, which is the first novel therapy approved for Alzheimer's disease in the U.S. since 2003, is developed by American biotechnology company Biogen with Japan's Eisai Co.

It is manufactured from living cells and will be given at a doctor's office or hospital. It is to be given as an infusion every four weeks.

"Alzheimer's disease is a devastating illness that can have a profound impact on the lives of people diagnosed with the disease as well as their loved ones," said Patrizia Cavazzoni, director of the FDA's Center for Drug Evaluation and Research.

Currently available therapies only treat symptoms of the disease, while this treatment option is the first therapy to target and affect the underlying disease process of Alzheimer's, according to Cavazzoni.

A controversial decision

The decision, which could impact millions of Americans and their families, has sparked disagreements among medical researchers, AP reported. 

The drug did not reverse the mental decline, but only slowed it, AP reported, citing a study.

Patients taking aducanumab saw their thinking skills decline by 22 percent more slowly than patients taking a placebo.

But that meant a difference of just 0.39 on an 18-point score of cognitive and functional ability. And it's unclear how such metrics translate into practical benefits, like greater independence or the ability to recall important details. 

Dr. Caleb Alexander, an FDA adviser who recommended against the drug's approval, said he was "surprised and disappointed" by the decision.

"The FDA gets the respect that it does because it has regulatory standards that are based on firm evidence. In this case, I think they gave the product a pass," said Alexander, a medical researcher at Johns Hopkins University.

The FDA's top drug regulator acknowledged that "residual uncertainties" surround the drug, but said Aduhelm's ability to reduce harmful clumps of plaque in the brain is expected to help slow dementia.

"The data supports patients and caregivers having the choice to use this drug," Cavazzoni told reporters. She said the FDA carefully weighed the input of people living with the "devastating, debilitating and deadly disease."

Under terms of the so-called accelerated approval, the FDA is requiring Biogen to conduct a follow-up study to confirm benefits for patients. If the study fails to show effectiveness, the FDA could pull the drug from the market, though the agency rarely does so.

The company said it aims to complete the FDA-mandated follow-up trial by 2030.

The FDA's review of the drug has become a flashpoint in longstanding debates over standards used to evaluate therapies for hard-to-treat conditions. On one side, groups representing Alzheimer's patients and their families say any new therapy – even one of small benefit – warrants approval. But many experts warn that green-lighting the drug could set a dangerous precedent, opening the door to treatments of questionable benefit. 

A high price

Biogen said the drug would cost approximately $56,000 for a typical year's worth of treatment, and said the price would not be raised for four years. Most American patients won't pay anywhere near that thanks to insurance coverage and other discounts.

About 900 U.S. medical facilities are ready to begin prescribing the drug, according to Biogen, with many more expected in the coming months.

Biogen shares jumped by 38 percent in trading Monday on the news, with analysts forecasting billions in future sales. The Cambridge, Massachusetts-based company plans to begin shipping millions of doses within two weeks.

The non-profit Institute for Clinical and Economic Review, which studies drug value, said Biogen's drug would have to halt dementia entirely to justify its $56,000 per-year price tag.

The pharmaceutical industry's drug pipeline has been littered for years with failed Alzheimer's treatments. The FDA's green-light Monday is likely to revive investments in therapies previously shelved by drugmakers.

About Alzheimer's

Alzheimer's is an irreversible, progressive brain disorder that slowly attacks areas of the brain needed for memory, reasoning, communication, and basic daily tasks. In the final stages of the disease, those afflicted will lose the ability to swallow.

Some 6 million people in the U.S. and many more worldwide suffer from it. The global burden of the disease, the most common cause of dementia, is expected to grow as millions of more baby boomers progress further into their 60s and 70s.

Researchers don't fully understand what causes Alzheimer's, but there's broad agreement the brain plaque targeted by aducanumab is just one contributor. Evidence suggests family history, education, and chronic conditions like diabetes and heart disease may all play a role.

"This is a sign of hope but not the final answer," said Dr. Richard Hodes, director of the National Institute on Aging, which wasn't involved in the Biogen studies but funds research into how Alzheimer's forms. "Amyloid is important but not the only contributing factor."