LOS ANGELES (AP) — Authorities say black tar heroin in Los Angeles may be contaminated with bacteria that can cause death, putting injection drug users at greatest risk.

The Los Angeles County Department of Public Health says Tuesday it’s investigating three suspected cases of wound botulism from heroin use.

The illness can be mistaken for a drug overdose and includes symptoms including drooping eyelids, blurred vision and trouble breathing.

Officials warn that contaminated drugs look the same as drugs that do not contain bacteria. And “cooking,” or heating, the heroin will not kill the bacteria.

Botulism can spread between users who share needles.