Montreal police said Monday they found a Can$3 million (US$3 million) drug stash that included their first ever black market discovery of a synthetic drug that is "40 times stronger than heroin."

Authorities seized more than 300,000 tablets of the illegally-produced synthetic prescription drug desmethyl fentanyl, as well as marijuana, hashish and ecstasy from a makeshift Montreal laboratory on April 25, said a statement.

So powerful is the drug that one of the policemen involved in the bust was hospitalized with heart palpitations after briefly coming in contact with it, even though he was wearing a protective mask.

Some of stash was headed for the United States.

Two people were arrested.