Paramedics in Canada's largest city responded to 173 opioid overdose calls over the civic long weekend, making it the highest number on record.
In a warning, Toronto Public Health said "while specific details are not yet known, there appears to be a range of substances from the unregulated drug supply involved".
"Toronto's drug checking service has reported finding unexpected, highly potent drugs in samples checked from the unregulated drug supply in recent months, including 'ultra potent' opioids (such as carfentanil, etonitazene, and isotonitazene) and etizolam (a benzodiazepine-related drug)."
The warning comes after Toronto police issued their own, following rise overdose calls, which included 4 deaths in 53 Division.
CP24 reports Ontario's Chief Medical Officer of Health Dr Kieran Moore also addressed the issue, but said that the government wants to first "get COVID under control.
"We need to double down on all we're doing from an addictions mental health vantage point, to opioid agonist therapies to Naloxone to consumption and treatment sites to enhance rapid access addiction medicine clinics and harnessing primary care emergency medicine to be able to provide for the needs of these patients.
"I am very aware of its devastation to families at a very deep and personal level, and I just want to assure you I will be fully committed to responding to this threat on an ongoing basis once we can get COVID under control and we've started working on that strategically within my office already."
In the month of June, Paramedics in Toronto responded to 448 non-deadly overdose calls and 24 deadly overdose calls, compared to 202 non-deadly calls and 13 deadly calls in June 2020.
Toronto has had to endure some of the longest and toughest lockdowns in the world, which experts have said is a contributing factor in the rise of opioid deaths.