BYRAM, Miss. (AP) — Mississippi officials are warning that synthetic marijuana they seized at a Brandon convenience store on Aug. 8 is laced with the powerful opioid fentanyl.

Mississippi Bureau of Narcotics Director John Dowdy says the state crime lab detected the fentanyl.

The opioid is a frequent cause of overdoses in opioid users.

Dowdy says the discovery proves the danger of using synthetic marijuana, often called spice, noting it’s illegal and unregulated.

Officials searched nine Rankin County businesses last week, seizing 24,000 doses of synthetic marijuana, making seven arrests and seizing more than $350,000 in bank deposits