The Food and Drug Administration has approved Biogen’s controversial Alzheimer’s drug aducanumab. This is the first federally approved treatment for Alzheimer’s in almost 20 years.

US regulators say the drug, which will be marketed as Aduhelm, is the first-ever that can treat the underlying disease and its memory-robbing effects, rather than just treating symptoms like anxiety and insomnia.

The approval of this drug brings home to the more than 6 million Americans currently living with the disease. However, some doctors say the drug won’t help all patients, particularly those with more advanced cases of the disease.

Meanwhile, other health professionals say that the evidence supporting the drug’s efficacy is limited.

The FDA’s own outside advisers have said that the data behind the drug is not strong enough. Some even criticized the FDA’s own staff for what it called an overly positive review.

“We are well-aware of the attention surrounding this approval,” Dr. Patrizia Cavazzoni, director of the FDA’s Center for Drug Evaluation and Research, said in a statement.

“We understand that Aduhelm has garnered the attention of the press, the Alzheimer’s patient community, our elected officials, and other interested stakeholders,” she continued.

“With a treatment for a serious, life-threatening disease in the balance, it makes sense that so many people were following the outcome of this review.”

The drug has garnered controversy since it first showed signs of benefits in 2016. In 2019, Biogen paused trials of the medication after an independent group said early data showed it was unlikely to work. 

But months later, the company announced it would seek regulatory approval for the drug anyway.

The FDA greenlight should be a boon for drugmaker Biogen, which is struggling amid declining sales and the loss of patent protection for one of its major drugs, Tecfidera, a pill for multiple sclerosis.

The agency approved aducanumab through its Accelerated Approval pathway to treat people with mild cases of cognitive impairment or dementia, whose brains have accumulated beta amyloid. Many researchers believe the protein plays a significant role in Alzheimer’s disease in patients.

“This historic moment is the culmination of more than a decade of groundbreaking research in the complex field of Alzheimer’s disease,” Biogen CEO Michel Vounatsos said in a statement. 

“We believe this first-in-class medicine will transform the treatment of people living with Alzheimer’s disease and spark continuous innovation in the years to come.”

There were more than 120,000 deaths from Alzheimer’s in the US in 2019. That was up over 50 percent from a decade earlier, according to the Centers for Disease Control and Prevention.

Instead of ruling on the drug by looking solely at its effects on cognitive decline in patients, the FDA granted a conditional approval based on Aduhelm’s ability to clear beta amyloid. 

Biogen still has to complete a large clinical trial to confirm that removing the beta amyloid has benefits when it comes to cognitive decline, the FDA said. The agency can still rescind approval if the results of that study are lackluster.

Shares of Biogen were paused before the announcement.