The Ontario College of Pharmacists has launched an investigation after fentanyl was found in a naloxone kit assembled at an undisclosed pharmacy somewhere in the province.

According to a report in the Toronto Star, the powerful opioid was located in a kit that was given to a customer at a Shoppers Drug Mart on Monday.

Naxolone is used to reverse the effects of an opioid overdose.

The drug can be administered through injection or nasal spray and is available for free at participating Ontario pharmacies.

“The pharmacy is fully cooperating and we are confident that immediate action has been taken to begin to determine how this happened and how it could have been prevented,” Ontario College of Pharmacists Spkesperson Todd Leach told CP24 in a written statement. “We have not been made aware of any similar incidents occurring at other pharmacies.”

Leach said that the investigation into how fentanyl came to be included in a naloxone kit is ongoing and therefore no further information can be released.

When asked for comment, a spokesperson for Shoppers Drug Mart told CTV News Toronto that the discovery is “a case of human error.”

“We share the view that this is a considerable error, and one that absolutely should not have happened. Our local pharmacist-owner took immediate action to ensure consumer safety, visiting the customers to secure the product and provide the correct medication, and to offer a detailed apology,” spokesperson Catherine Thomas said via email.

“We are taking appropriate steps to reinforce professional and operational expectations and procedures to help prevent this type of unfortunate situation from reoccurring.”

Thomas went on to call the mishap an “isolated event” and said customers should continue to feel confident in Naloxone kits as an “effective response for accidental opioid overdose.”

Naloxone works by temporarily removing the opioids from the receptor sites in the brain and can be administered through injection or nasal spray. Currently, kits of both kinds are available for free at pharmacies across Ontario, with Rexall announcing today that all its locations will dispense them.