Five people were arrested in the Grand Forks area this week for selling pills laced with the powerful painkiller fentanyl.
Grand Forks police lieutenant Brett Johnson said more than 500 pills were seized.
Johnson said the pills might be linked to three overdose cases in the region.
"It's hard to tell how widespread the problem is," Johnson said. "The pills can be ordered over the internet or over the dark web and that makes it pretty difficult to determine how widespread the problem is."
The pills are made to look like prescription oxycodone, but Johnson said pills made in a clandestine lab can contain unknown drugs. In this case the pills were tested and found to contain fentanyl.