A couple found dead by their four children in a southwest Calgary home apparently died of a drug overdose — in what a veteran police officer describes as one of the most tragic incidents he has ever witnessed.

Their bodies were found on Sunday, police say. The couple had four children, ranging in age from four to 14.

The man and woman, both in their 30s, died of an apparent drug overdose, said Staff Sgt. Mark Hatchette.

​"We have a couple of victims who by all indications were drug users ... there's no indication of any foul play," he said.

"Which would suggest, potentially, they were using drugs that they didn't know what the drugs contained."

Hatchette said evidence suggests the pair were users but not traffickers.

'Tragic circumstance'

"It's a really sad case, you have four children who woke up one morning and discovered they no longer have parents," said Peter Choate, an assistant professor of social work at Mount Royal University.

''These parents didn't intend to abandon their children so let's be clear that this was a tragic circumstance with

people trying to cope with something in their lives that they were having trouble managing otherwise."

Choate said there should be more support for people who use drugs in order for them to cope with their problems.

Police said the children are safe, but would not say where they are.

Carfentanil deaths

The type of drug involved will not be known for months until toxicology reports are available, officials said.

The deaths came just a day before the province announced that carfentanil — a toxic opioid that is 100 times more potent than fentanyl — is now linked to 15 deaths in Alberta.

Fourteen of the deaths occurred between September and the end of November.

There were five deaths in Calgary, seven in the Edmonton area and three in small rural centres.

The age range for all but two of the people who died was between 20 and 40.