The highly toxic opioid carfentanil has appeared in Toronto, with police announcing Wednesday they have seized heroin laced with the drug considered to be 10,000 times more potent than morphine.

Carfentanil was only publicly confirmed to be in Ontario on Tuesday. Waterloo Regional Police announced that an analysis of 85 counterfeit pills seized there showed they contained amounts of carfentanil rather than OxyContin.

No amount of the drug is safe for human consumption, public health officials say. It's designed to sedate large animals — like moose and elephants — and even one microgram will cause a reaction in humans.

A grain of salt

To put that in perspective, a grain of salt weighs at least 100 times that amount — and that's why Toronto Public Health officials say that just one grain can be fatal.

"In very tiny doses, it can be deadly," said Dr. Rita Shahin, the agency's associate medical health officer. "Use of just a small amount of a drug containing carfentanil can cause an overdose, and likely a fatal overdose."

Carfentanil has not yet been tied to any deaths in Ontario.

Alberta, however, has recorded at least 15 fatalities connected to the opioid. Health Canada reported the presence of carfentanil in Vancouver street drugs in September and police in that province say that at least one person has died of a related overdose.

Carfentanil was produced to sedate large animals, like elephants and moose. It's deadly to humans. (Dave Orrick/Associated Press/Pioneer Press)

The drug looks almost identical to table salt and has no distinctive smell or taste.

Toronto Public Health issued a warning to opiate users Wednesday about carfentanil tainting local street drugs. Naloxone can be used to reverse an opiate overdose and it's available at the city's harm reduction clinic, The Works, and for free at many pharmacies.

The Works also offers training to administer naloxone to someone in distress.

And ​Dr. Shahin said public health officials will increase the amount of naloxone they give out to users and to their friends and family. A carfentanil overdose would need a much higher dose of the antidote than other street drugs would to block the effect of the potent opioid, the associate medical health officer said.

It's also crucial for the city to move ahead with opening the three supervised injection sites approved by council in June now that carfentanil has shown up in Toronto, Shahin said.

"With something like carfentanil, having a medical response right on site is really critical in terms of helping people recover."