US approves first new Alzheimer's drug in 20 years

US regulators on Monday approved Biogen Inc's aducanumab as the first treatment to address an underlying cause of Alzheimer's disease despite controversy over mixed clinical trial results for the drug.

Aducanumab aims to remove sticky deposits of a protein called amyloid beta from the brains of patients in earlier stages of Alzheimer's in order to stave off its ravages, which include memory loss and the ability to care for one's self.

The Food and Drug Administration said that the clinical trials for the treatment, to be sold under the brand name Aduhelm, showed a reduction in the plaques that is expected to lead to a reduction in the clinical decline of patients.

"Although the Aduhelm data are complicated with respect to its clinical benefits, FDA has determined that there is substantial evidence that Aduhelm reduces amyloid beta plaques in the brain and that the reduction in these plaques is reasonably likely to predict important benefits to patients," the agency said in a statement.

Biogen's drug had been hailed by patient advocates and some neurologists eager to have an effective option for patients with the lethal disease. Other doctors said clinical trial results were inconsistent and more proof was needed.

The FDA said Biogen must conduct a post-approval clinical trial to verify the drug's clinical benefit.

"If the drug does not work as intended, we can take steps to remove it from the market," it said.

Aducanumab was studied in patients with early disease who test positive for a component of amyloid brain plaques. Some trial patients experienced potentially dangerous brain swelling.

Biogen has estimated that around 1.5 million Americans would be eligible for treatment with aducanumab, which is given by monthly infusion, raising concerns about costs to the healthcare system.

Shares were halted pending the news.