Pills that look like Xanax but contain the powerful opioid fentanyl have been linked to nine deaths in Pinellas County, Florida in recent weeks.

The pills are killing people within minutes, WFLA reports. Pinellas County Sheriff Bob Gualtieri said, “You don’t have to take a handful of them. All you gotta do is take one, and you’re dead.”

Authorities do not know who is making the pills or where they are coming from. The pills are selling for $5 each, the article notes.

According to Dr. Raafat Hanna, an emergency room physician at Northside Hospital in Pinellas County, fentanyl is 80 to 100 times as strong as morphine and about 40 to 50 times more times as strong as street heroin. “It’s easy to get overdosed [sic] on a very small dose,” he said.