According to a major new study, a pain medication that millions of Americans rely on for chronic back pain may come with a hidden risk: a significantly higher chance of developing dementia or other cognitive problems.

Researchers from Case Western Reserve University and many partner institutions analyzed medical records from 68 health systems across the United States, comparing 26,414 adults prescribed gabapentin for persistent low-back pain with a matched group who had similar pain — but didn’t take the drug.