Biogen Inc. has been given U.S. Food and Drug Administration authorization for its Alzheimer's treatment aducanumab, or Aduhelm, many reports said Tuesday.

The administration approved Biogen's treatment based on research results showing it is "reasonably likely" to benefit Alzheimer's patients.

The drug, which Biogen developed with Japan's Eisai Co. Ltd., intends to reduce the mental deterioration for patients with Alzheimer's, the sixth deadliest disease in the U.S.

It is the only therapy U.S. regulators have said has the capability to treat the underlying disease - rather than manage common symptoms like insomnia and anxiety.

The approval of the first new drug for Alzheimer's disease comes after almost 20 years - despite controversy over mixed clinical test results for the therapy.

Independent advisers claim the drug hasn't been proven to help slow the brain-destroying disease.

The administration's approval, which could affect millions of Americans, might trigger disputes among doctors, medical researchers and patients, according to The Associated Press.

Alzheimer's disease is a progressive neurodegenerative disorder that gradually impairs memory and thinking skills.

Based on data by the Alzheimer's Association, more than 6 million Americans are suffering from the disease. It is estimated that by 2050 that figure would increase to almost 13 million, the group said.

Alzheimer's patients and their families, some of whom have waited for years for a new drug to be developed, were happy after the news.

"Today is a huge day for us in the Alzheimer's community. I was elated," Jeffrey Borghoff, 57, an early Alzheimer's sufferer from New Jersey, said.

Meanwhile, Biogen chief executive Michel Vounatsos told CNBC that the list price of $56,000 a year for the company's new Alzheimer's disease drug aducanumab is "fair."

The Massachusetts-based biotech company said it will not increase the price of the medication for the next four years.