The couple — both in their 30s — were found dead in their home on July 20, and the use of illicit drugs was suspected at the time. They are survived by their two-year-old son, Magnus.
"Expedited toxicology testing confirmed that both Mr. and Ms. Leighton had ingested toxic levels of fentanyl in combination with other drugs," a statement from the Coroners Service said.
According to family, the couple were celebrating a move to a new North Vancouver rental home with a yard for their toddler.
Health officials say the Leightons fit the profile of recent overdose deaths linked to fentanyl.
"We know the people who are dying in British Columbia are not injection drug users," Vancouver Coastal Health medical officer Dr. Mark Lysyshyn told CBC News.
"They're people who are taking their drugs by inhalation or by ingestion or snorting them. They're people I guess we would describe as more intermittent drug users. They're not people who live in the Downtown Eastside."
Fentanyl is a synthetic opioid, much more toxic than morphine, that is often mixed with other illicit drugs.
Recreational drug users with a low tolerance for opioids are particularly at risk from fentanyl, the Coroners Service said.
The percentage of drug overdose deaths where fentanyl was found has risen to more than 25 per cent in British Columbia in the past three years, according to the coroners service.
More than 80 per cent of those deaths were caused by a mixed drug overdose.