Detectives are looking at whether the Russian anti-anxiety drug Phenibut is behind a mass overdose of students at a private school on Queensland's Gold Coast.

Police said the seven teenagers took varying amounts of a "powdered drug" that may have been bought online.

While toxicology reports haven't been finished, the incident has put the drug, which was once given to cosmonauts, in the spotlight.

We take a look at what the drug is, and why experts are concerned.

What is Phenibut?

Phenibut is an anti-anxiety drug also used to improve sleep.

The neuropsychotropic drug was marketed as a supplement but is often used as a recreational drug.

It's been accessible since the 1960s.

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

Phenibut gained prominence when it was included as part of standard supply in medical kits for cosmonauts on Russian space flights.

Dr Treasure McGuire from the University of Queensland school of pharmacy said the drug was "strongly tranquilising".

"Based on the dose that's used, you can move from where it might have been used therapeutically for anxiety or for insomnia to a drug that can be quite sedating and quite dangerous," she said.

"Certainly stupor or lethargy, altered mental state can occur."

Is it legal?

Earlier this month, the Therapeutic Goods Administration officially listed Phenibut as a Prohibited Substance, meaning that its possession, use, sale or manufacture is now banned in Australia.

Until the ban, Phenibut capsules were easy to purchase legally in bulk from Australian websites selling fitness supplements.

On one popular website, there was no mention of the serious concerns held by the TGA about the safety of the drug, with sellers instead spruiking the so-called "clear cognitive benefits".

Some users said the drug helped improve social anxiety and sleep, while others warned of its addictive nature.

The TGA ban, however, does not prevent people from purchasing it online from countries like Russia.

It is therapeutically prescribed in eastern European countries, but legally available in few others.

The banned drug Phenibut is still being sold online overseas as a supplement. ( ABC News )

What is the danger?

The danger is in prolonged use, which can result in a dependence and tolerance for the drug.

Experts said the availability of powder increases risk of toxicity and overdose.

Possible side effects included central nervous system depression, as well as delirium and seizures potentially requiring intubation and ventilation.

Other side effects include sedation, somnolence, nausea, irritability, agitation, anxiety, dizziness and headaches.

The biggest danger is in overdosing, which can lead to coma and ICU hospital admission requiring advanced life support.

Withdrawal symptoms include hallucination, agitation, anxiety, insomnia, abdominal pain, vomiting and toxicity.



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

What's the message from experts?

Dr McGuire said the fact it's so easily and cheaply available online is "a great concern, but that's the world we live in now".

"What we have to do is educate," she said.

"For me the important message for the general public and the young adolescents is "this is dangerous".

"It's not smart to take something you don't have an understanding of how it works, how much you should take. So the harms well and truly outweigh the potential benefits of a very short stimulus.

"In the unsuspecting thrill seeker like an adolescent, you're more likely to cause much more harm."