Police have said a Russian anti-anxiety drug is on their radar as they investigate a mass overdose involving students at a Gold Coast private school.

Seven boys, aged 14 and 15, were taken to hospital from Saint Stephen's College in Upper Coomera on Wednesday, and four remain in a critical condition.

The school said two of the boys had been discharged.

Detective Senior Sergeant Greg Aubort said police had not yet identified what substance the group had ingested, but confirmed they were looking at the anti-anxiety drug Phenibut.

Phenibut has similar effects to the party drug GHB, and earlier this month the Therapeutic Goods Administration (TGA) declared it a prohibited substance.

Students arrive at Saint Stephen's College a day after seven of their schoolmates were hospitalised. ( ABC News: Tom Forbes )

The TGA said usage across the country was increasing but Phenibut carried a "high risk of dependency, abuse [and] misuse".

Senior Sergeant Aubort said the teenagers had taken varying amounts of the "powdered drug" at different times of the day.

"Individuals took different doses, some small some large ... everything from the taste to what I call a significant amount which was clearly dangerous," he said.

Investigators believe the drugs were purchased online, possibly on the dark web, and Detective Sergeant Aubort said the teenagers could potentially face drug supply charges.

"We investigate crimes so at the end of the day if the evidence supports criminal charges then yes we will be pursuing that," he said.

He said they were liaising with several departments including Border Force, the State Crime Operation Command and the drug squad.

"We'll deal with this situation at hand what happened yesterday and from that we'll look at that flow-on effect as to where it came from and how it came in,"

Students' phones have been seized and parts of the school remain cordoned off as investigations continue.

Incident shocks school community

This morning the Gold Coast Health Service listed four of the boys as being in an unstable condition, but said their conditions were "steadily improving".



In a letter to parents this morning, Saint Stephen's College principal Jamie Dorrington said the school's primary focus has been on the welfare of the students in hospital and providing counselling.

"The past 24 hours have been a particularly distressing and emotional time for our school community," he said.

"We are cooperating fully with the Queensland Police Service's investigation into the incident. The police are best placed to thoroughly examine how and why this occurred."

Meanwhile some worried parents are now weighing up their options.

"It is going to happen anywhere, but you would like to think at a GPS-type school that you would have less of issue. I will have to seriously consider if I leave my children at this school to be honest," parent Greg Peters said.

"I'm disappointed that it has happened, but it is not the school's fault."

Another parent also defended the school, saying he was disappointed to hear of the overdose.

"Some boys obviously made some bad decisions which will always happen but I have enormous confidence in Saint Stephen's doing the right thing and taking care of the kids," he said.

"We just hope that the kids that got themselves in trouble yesterday recover fully."

Paramedics and police at Saint Stephen's College. ( ABC News: Tom Forbes )

Drug use not as rare as parents think, expert says

University of Queensland drug expert Professor Jake Najman said it was not easy for just anyone to buy drugs through the dark web and hide your identity.

"So how these people have managed to do it, we need to know about that so that we can stop other young people from doing it," he said.

Professor Najman said it was important for authorities to figure out who supplied the drugs and where they came from.

"They are rumoured to be related to GBH but whether they've tweaked it or found some other chemical composition associated with them we don't know," he said.

"It just seems very, very strange.

"This sounds like a deadly mixture that is being sold and you wonder who the heck is selling this kind of mixture and why people didn't find out about it.

"This is in fact the largest negative reaction, nasty consequences of an unknown product, that I have ever heard of and it raises the questions for who manufactured this and what they have put in it."

However he warned parents that drug use by teenagers at school was fairly common.

"[We're] talking maybe even 30 per cent of young people at school experimenting with drugs, so the notion that kids trying drugs at school is rare and unusual is unlikely," he said.

"Young people will often exchange drugs and share drugs as part of a social activity, but the vast majority who do this rarely have a negative effect."

However Professor Najman said it was extremely rare to see such a dangerous mass drug overdose like this one at a high school.

"I've never heard of anything like it, it's really a one-off,"

"This kind of serious reaction we are dealing with, I'd say, we usually only see a handful of cases a year in Queensland."