The first new drug to treat Alzheimer’s Disease in nearly two decades was approved by the Food and Drug Administration (FDA) Monday. The medication, brand name Aduhelm, is administered intravenously once a month. It’s purported to slow cognitive decline in individuals with mild disease.

While it’s not the first Alzheimer’s drug ever developed, Aduhelm is the first drug to do more than just address the symptoms of Alzheimer’s. “It’s designed to remove amyloid beta plaque from the brains of individuals living with Alzheimer’s disease,” says Charles J. Fuschillo, Jr., President and CEO of the Alzheimer’s Foundation of America (AFA). Currently, the as-of-yet unproven hypothesis fueling this approach is that reducing this plaque buildup early on in the disease’s progression can slow onset of the disease’s symptoms and possibly lessen severity of disease down the line.

The FDA’s approval is not a wholesale endorsement of the drug, however. Existing evidence of its efficacy is controversial and Biogen, the drug’s manufacturer, is actually required to conduct another trial to prove that Aduhelm is effective, even as it goes to market now.

“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,” Patrizia Cavazzoni, MD, the FDA’s director of the Center for Drug Evaluation and Research, wrote on the agency’s website.

If the new trial fails to verify the drug’s clinical benefits, the FDA may initiate proceedings to withdraw its approval, says Fuschillo. In the meantime, some experts worry that the drug’s unproven, potential benefits are outweighed by its risks, which include swelling and bleeding in the brain experienced by a whopping 40 percent of Phase 3 trial participants. The drug is also not cheap. “They’re estimating approximately $4,300 per fusion, upwards of $56,000 on an annual basis,” says Fuschillo.

Despite this—and the uncertainty around the drug’s efficacy—Fuschillo says the AFA is cautiously optimistic about Aduhelm. “We’re concerned about the cost of the drug, and the most common side effects,” he says. “However, the approval of this drug by the FDA is the first approval of any Alzheimer’s disease drug in more than two decades, and we are hopeful that it shows positive results in the fight against Alzheimer’s disease and improves quality of life for individuals living with it.”

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