A new experimental drug developed to treat Alzheimer’s disease has been found to harm – rather than boost – memory, according to a new study in mice.

Northwestern University biologist Robert Vassar warned that the drug designed to block the development of so-called amyloid plaques in the brain that are a hallmark of Alzheimer’s patients also appears to interfere with wiring in the brain linked with memory.

Vassar, who presented his findings in the journal Molecular Neurodegeneration, said his study of mice should not halt experiments of the drugs, but suggests researchers need to be cautious.

Drugs based on the technique have not been approved by the U.S. Food and Drug Association, but are being tested by pharmaceutical companies for possible wider use.

“Let’s proceed with caution,” Vassar said in a statement on the research, issued at the annual meeting of the American Association for the Advancement of Science. “We have to keep our eyes open for potential side effects of these drugs.”