A member of the FDA advisory committee who stepped down after the regulating body's approval of, a controversial , claims the treatment "showed no good evidence that it worked."
Harvard professor of medicine Dr. Aaron Kesselheim, who also works at Brigham and Women's Hospital, called it the "worst drug approval decision in recent U.S. history" in his resignation letter.
"It had important side effects," Kesselheim told CBS News' Dr. Tara Narula. "The FDA's totally switching gears over the last six months, and approving this drug on the basis of a theory relating to the surrogate marker of amyloid plaques that we, as an advisory committee back in November, were told to not consider."
A number of critics are blasting the FDA's approval of Aduhelm. Clinical trials showed it may reduce amyloid plaque, which is believed to be a marker of.
However, it is not clear whether it delays or prevents actual symptoms, and the FDA's independent advisory committee recommended the agency reject the drug.
After the FDA ignored the advice, Kesselheim and two other committee members resigned.
The first patient who was not part of a clinical trial got the drug last week.
Side effects can include headache, ARIA-Edema, ARIA-H microhemorrhage, ARIA-H superficial siderosis and fall, according to the FDA.
"If the FDA allows companies to get drugs approved on the basis of trials that are stopped early, trials that are reanalyzed, that sets a precedent because it tells other companies, 'Well, I don't also — I don't need to run a rigorous trial either,'" Kesselheim said.
He said patients and physicians both rely on the FDA to hold "reasonable standards."
"In the majority of cases, I'd like to think that the FDA makes the right decision," he said. "In cases like this, where the FDA makes what I think is the wrong decision, I think that we need to understand better why the decisions were made in this way."
Biogen tells CBS News it gave the FDA 2.2 million pages of data and analysis from eight clinical trials. An FDA official told reporters that "the dataset for Adulhelm was very complex and our review has been thorough."