GHB is a class B drug, which the World Health Organisation says has lead to comas, and from which there have been reported deaths around the world.
Police said they were concerned at the number of people who had needed hospital treatment, but were not sure if the cases were linked.
Detective Senior Sergeant Marcia Murray said they were waiting on toxicology tests to confirm what a man and woman, who were treated yesterday, had taken.
"Any illegal substance is dangerous, we don't know what those other people have taken.
"People are being transported to hospital with Status 1, Status 2 conditions, which is life-threatening."
She said the pair's hospitalisation led the police to the other cases, which will be investigated.