With the changes the label says the drug has not been studied in treating later stages of the disease and should be given to patients with "mild cognitive impairment or mild dementia stage of disease."
Shares of the Cambridge, Mass., drugmaker at last check were up 2.5% to $364.06.
Biogen, which partners on the drug with Japan's Eisai ESALY, said in a statement that the update emphasizes information about the disease stages studied in the Aduhelm clinical trials.
"Treatment with Aduhelm should be initiated in patients with mild cognitive impairment or mild dementia stage of disease, the population in which treatment was initiated in clinical trials," the updated language reads.
"There are no safety or effectiveness data on initiating treatment at earlier or later stages of the disease than were studied."
Alfred Sandrock, head of research and development at Biogen, said in a statement that “based on our ongoing conversations with prescribing physicians, FDA and patient advocates, we submitted this label update with the goal to further clarify the patient population that was studied across the three Aduhelm clinical trials that supported approval."
The FDA cleared Aduhelm for marketing last month, saying that it reduced the amounts of amyloid, a sticky substance in the brain linked to Alzheimer's.
Critics of the drug have said that this substance hasn't been shown to actually drive the disease, The Wall Street Journal reported.
Three members of an FDA advisory committee that assessed the drug resigned from the panel, questioning whether the drug works.
Some analysts upgraded the company after the FDA's approval.