Paramedics were called to Saint Stephen’s College in Queensland after seven students were left with an “altered level of consciousness”.
The year 10 boys filmed themselves taking the pills which were based in Australia earlier this month.
Police are now looking into whether the powerful drug was purchased over the mysterious dark web.
Police inspector Tony Wormald said: “We are making some inquiries as to whether or not they have actually purchased it on the internet themselves.
He added that the situation was “very serious”.
The dark web is a hidden area of the internet beyond the reach of Google where users can operate anonymously.
This has made it a hotbed of illegal activity.
Police confirmed that the Russian-made phenibut pill had led to an “altered level of consciousness” among those who took it and had left at least five pupils in a serious condition in hospital.
It is believed the boys were aged 15 and 14.
Phenibut is used to treat anxiety and was first used in Russia in the 1960s.
A video of the incident has been shared on the social media app Snapchat and appears to show the label of the pills’ container and the dosage the students were taking.
Police have urged students not to share the video and have oozed the phones of students with copies of it.
An email from the school headmaster, Jamie Dorrington, told parents to direct their children not to share the footage.
The email said: “If your child receives any messages or film footage or audio files relating to today’s incident they MUST NOT forward to any other person.
“This is not a request from my office but from the Queensland Police Service.”
The sinister dark web is largely used as an online black market where users can trade in illegal items such as firearms, drugs and indecent images of children.
Explaining the risk the Saint Stephen’s College students took by swallowing the illegal pill Pat Berry of Queensland Ambulance Service warned of a “Russian roulette”.
She said: “It would appear this was an overdose.
“We believe they have swallowed the drug.
“It’s just Russian roulette. “There really is no such thing as a recreational drug.”