WASHINGTON -- U.S. health authorities are warning about reports of injury, addiction and death with a herbal supplement that has been promoted as an alternative to opioid painkillers and other prescription drugs.

The supplement, kratom, is made from a plant native to Southeast Asia. It has gained popularity in the U.S. as a treatment for pain, anxiety and drug dependence. Users have opposed efforts to regulate the plant, saying it could be a safer alternative to opioid pain pills.

But the Food and Drug Administration said Tuesday that kratom carries similar risks, including addiction and death, and the agency is working to block shipments.

The FDA said it is aware of 36 deaths involving products made with kratom and hundreds of calls to poison control centres.