The Overdose Prevention Network of Niagara is warning about a tainted supply of street dugs in Niagara.
OPENN Co-Chair Glen Walker says sedatives and stimulants are being added to illegal opioids.
"What we're seeing is a sedative being mixed in with the opioid so it really does depress the system and can cause respiratory failure. Naloxone will bring you out of the opioid portion of the overdose, but not the other portion of the overdose."
Walker says officials at the St. Catharines overdose prevention site have had a couple of deaths in the last week or so.
He encourages anyone who is using illegal drugs not to use alone.
"It's really about doing CPR, calling 911 right away to get that assistance so they can get oxygen going for these folks and provide more effective medical intervention."