Detectives have searched private residences as well as businesses in Mackay, Rockhampton, Bundaberg and Toowoomba that were believed to be selling the synthetic drug.
Packet of synthetic cannabis. Source: 7News
Detective Acting Inspector Darrin Shadlow said one of the individuals who passed away only had one draw of the smoke and never regained consciousness.
No arrests had been made but shop owners were being spoken to, a police spokesman told AAP.
The businesses were part of the same franchise.
Mackay health authorities have warned of a recent increase in the number of hospital patients complaining of adverse effects associated with the synthetics.
The fatalities prompted police to warn that synthetic drugs, commonly bought over the internet, are covered under drugs misuse legislation.
Detective Acting Superintendent Darrin Shadlow said, "We're really wanting to get the message out there to the public that this stuff that people are selling is highly dangerous."Having possession of this synthetic cannabis is illegal. It is just as illegal as possessing cannabis. So if you think you're buying a product from a registered store or business it is still illegal. And it is illegal for these people to be selling it.
"Any compound that intends to mimic a dangerous drug, is deemed to be a dangerous drug."
Investigations are continuing.
"We will target any store or any person that is in possession or selling this type of product," he said.