Two Milton teens who police speculated may have suffered opioid overdoses last month actually ingested synthetic cannabinoids unknowingly, investigators said Wednesday.

The 18-year-olds were found unresponsive on the deck of a residence in Milton on the afternoon of May 15 after a neighbour called 911.

Halton Regional Police officers administered naloxone to the pair. The drug can reverse the effects of some opioid overdoses.

Police initially said that the pair were displaying symptoms consistent with opioid overdose. They were unconscious, their breathing was shallow and their pupils were dilated, and both were frothing at the mouth, according to officers who were at the scene.

Police said at the time that both teens quickly regained consciousness, apparently a sign that the naloxone had worked to neutralize opioids. They were then taken to hospital for further treatment and have since fully recovered.

Police also told reporters that the pair had gone outside to smoke what they believed to be cannabis, though they did not comment on whether the cannabis and the opioids were possibly related.

Investigators said Wednesday, however, that further testing by Health Canada and the Centre for Forensic Sciences revealed that the teens ingested synthetic cannabinoids — lab-made chemical substances that mimic some of the effects of pot.

The pair reportedly mixed the synthetic cannabinoids, which are illegal in Canada, with pot.

Teens thought they bought salvia

In another complicating twist, the teens actually thought they had purchased a substance called salvia, not synthetic cannabinoids. Salvia is a natural product made from the Salvia divinorum plant, which is found primarily in southern Mexico.

The plant has psychoactive properties and is technically illegal to sell in Canada because it is a natural product that has not been approved by Health Canada. Once a staple in head shops and even some convenience stores across the country, salvia has recently become more difficult to purchase.

The teens bought the synthetic cannabinoids, which police say came in a gold package labelled salvia, at an unidentified retail outlet somewhere in the GTA.

In a news release, Halton police warned that synthetic cannabinoids "are dangerous because there is no quality control in the preparation and packaging process.

"The contents of most synthetic cannabinoids are unknown, untested and can change from product to product. Synthetic cannabinoids are illegal in Canada, and unregulated," it continued.