The long, discouraging quest for a medication that works to treat Alzheimer’s reached a potentially promising milestone on Wednesday. For the first time in a large clinical trial, a drug was able to both reduce the plaques in the brains of patients and slow the progression of dementia.

More extensive trials will be needed to know if the new drug is truly effective, but if the results, presented Wednesday at the Alzheimer’s Association International Conference in Chicago, are borne out, the drug may be the first to successfully attack both the brain changes and the symptoms of Alzheimer’s.

“This trial shows you can both clear plaque and change cognition,” said Dr. Reisa Sperling, director of the Center for Alzheimer Research and Treatment at Brigham and Women’s Hospital in Boston, who was not involved in the study. “I don’t know that we’ve hit a home run yet. It’s important not to over-conclude on the data. But as a proof of concept, I feel like this is very encouraging.”

Aside from a couple of medications that can slow memory decline for a few months, there is no effective treatment for Alzheimer’s, which affects about 44 million people worldwide, including 5.5 million Americans. It is estimated that those numbers will triple by 2050.