The US Food and Drug Administration has approved a new medication for Alzheimer's disease. Aducanumab is the first new drug for the disease in 18 years.

US company Biogen and Japanese firm Eisai developed the drug. It targets plaques in the brain that researchers believe can affect cognition. Aducanumab is the first medication to tackle the disease process rather than just treating symptoms of dementia.

FDA regulators say clinical trials left them with some uncertainties regarding clinical benefits. They asked Biogen to conduct another trial. That process is expected to take years.

In the meantime, patients will be able to take the drug. More than 6 million Americans live with Alzheimer's disease.