The deadly opioid carfentanil has been blamed for two overdose deaths in Alberta prompting a warning from the province's chief medical officer of health.

"Albertans need to know that the drug carfentanil has made its way into our province and that it is an extremely dangerous and deadly opioid," Dr. Karen Grimsrud said in a statement Friday.

"The smallest trace of carfentanil can be lethal and Albertans should be aware of the life-threatening dangers in using this drug."

Earlier this week, the chief medical examiner notified Grimsrud that carfentanil was detected in two men in their 30s who died.

One of the deaths occurred in the Edmonton area, the other in Calgary.

Grimsrud said there's no precise reason why the deadly drug has appeared in Alberta, but discussions with colleagues in British Columbia suggest users aren't getting what they think they're buying.

"People often purchase drugs thinking it's one thing when in fact when they actually have it tested, it's another," she said.

There have been 153 fentanyl-related deaths in the first half of this year in Alberta compared to 139 deaths in the same period last year.

"We have an issue with opioids in this province," Grimsrud said.

Alberta's acting chief medical examiner, Dr. Elizabeth Brooks-Lim, said one of the men who died also had fentanyl in his system. She says it's likely carfentanil could have been in Alberta for a while, but hadn't been detected until now.

Few labs can detect

The small amount of the drug that causes death is part of the problem.

"Because it's such a very low level, you need particularly sensitive equipment to be able to pick up that lower level of the drug," she said.

One of the strongest opioids known, carfentanil is an analog of the synthetic opioid fentanyl, but 100 times more potent.

It was originally manufactured for veterinary purposes, designed to immobilize large animals like moose and elephants.

There is no known safe use of the drug for humans.

Carfentanil looks much like table salt and police have said a dose as small as a grain of sand could be fatal to humans.

Until very recently, toxicology tests could not confirm the existence of carfentanil in human blood due to the very low level of the drug needed to overdose.

Alberta's Office of the Chief Medical Examiner is believed to be the first toxicology laboratory in Canada to positively identify carfentanil in human blood.

Brooks-Lim said to the best of her knowledge, there are very few labs in North America capable of measuring carfentanil in human blood.