A new Alzheimer’s disease drug may be able to clear away goopy piles of toxic proteins in patients’ brains—hallmarks of the progressive disorder. The drug is an antibody directed at the proteins themselves, and the promising results come from a small, phase I safety trial.

To date, no other drug has shown this much brain-clearing power. If the results hold up in larger trials, the drug has the potential to prevent or even reverse the progression of the disease. But researchers caution that excitement should be tempered; it’s far too early to decipher the drug’s true potential. Similar antibody-based drugs have given promising results in early trials but went on to fail spectacularly in larger studies—in some cases even causing death.

“I am cautiously optimistic about this treatment, but trying not to get too excited,” Tara Spires-Jones, interim director of the Centre for Cognitive and Neural Systems at the University of Edinburgh, said in a media statement. “This was a small phase I study with 20-30 people in each treatment group. We will have to wait and see whether the promising results reported here are repeated in the larger phase III trials of this drug that are currently underway worldwide.”