Wellington-Dufferin-Guelph Public Health says four overdose deaths have been reported in eight days in Guelph and Wellington County.
Deaths have been reported in Guelph, Rockwood, Elora and Arthur since Feb. 21.
Public health said fentanyl is believed to be involved in each death, while red and purple-coloured versions of the deadly opioid were reported in at least two.
The agency is warning drug users that a stronger-than-normal substance is circulating in the area and that any coloured substance may pose a significant risk.
Anyone using illicit drugs is encouraged to never use alone, carry naloxone and take only 1/3 of a normal dose with any new purchase.
There is also the safe injection site at Guelph’s Community Health Centre in the city’s downtown core.
For those using alone, the National Overdose Response Service is a free anonymous service that can call drug users to check in on them. It can be reached at 1-888-688-6677.