The Duluth Police Department issued a news release today notifying the public of six drug-related overdoses occurring since Thanksgiving as result of the use of opioids. There have been no deaths, but the overdoses have prompted an investigation.

Opioids are substances that act on brain receptors to produce morphine-like effects. They come in tablets, capsules or liquid and are typically used to treat pain. Common opioids include heroin and prescription drugs like oxycodone, hydrocodone and fentanyl.

The DPD warns against using these drugs — particularly synthetic derivatives — because their content and purity is often unknown and can cause overdose deaths.