The prescription drug Xanax is being sold illegally to children on social media sites, a BBC investigation has found.
Xanax is widely prescribed in the US to treat anxiety but can only be obtained on private prescription in the UK.
Drugs charity Addaction said children as young as 13 had bought it online.
The Home Office said it was taking action. Instagram and Facebook said buying and selling drugs on their sites was prohibited.
BBC South East discovered drugs being advertised on Instagram and Facebook and bought what dealers claimed was Xanax and diazepam.
One teenager from Kent said people can search on social media to find dealers.
He admitted to using MDMA, cocaine and Xanax after contacting dealers online and said he spent his GCSE year trying drugs on school nights, and was on speed for most of his exams.
He said: "It is possible now to go on Instagram and find a drug dealer.
"You have to find a page which you could tell sold drugs, based on either their pictures or whatever."
He said the conversation then moves from social media to other apps which can't be tracked and are "safer to use".
Several young people in Sussex needed hospital treatment after taking Xanax , and last year up to 20 Wiltshire teenagers needed treatment after using the drug.
It has also been known to kill - rapper Lil Peep died from a suspected overdose last November leading US hip-hop stars to ask if lyrics about drugs were going too far.
London MP Bambos Charalambous said it was not known how widespread Xanax use was and called for an awareness campaign, further research and support services.
Nick Hickmott, from Addaction, said: "It's definitely part of our youth culture now.
"How many young people are using it is debatable, and obviously what's really important is we get some really good statistics around this and some really good records so we know exactly what we're dealing with, but it's enough to be showing some concern."
A spokesman for Pfizer, a pharmaceutical company which manufactures Xanax, said: "We are alarmed by the rise of counterfeit Xanax and its growing availability on the internet and dark web.
"Counterfeits are difficult to distinguish from the real medicines and are extremely dangerous by their very nature given that they are not produced under regulated manufacturing conditions to ensure their safety.
"We have found dangerous ingredients such as boric acid, heavy metals and floor polish in counterfeit medicines.
"We will continue to work side by side with all law enforcement agencies around the world to help detect, disrupt and deter counterfeit medicines trade."
A Home Office spokesman said: "We expect social media companies to have robust processes in place to act promptly to remove content and user accounts that do not comply with their own policies."
An Instagram spokesman said: "Buying or selling drugs is prohibited on Instagram and these accounts have been removed."
A Facebook spokesman said the accounts had been removed, adding: "Buying or selling drugs of any sort is not allowed on Facebook."
Both sites urged users to report such activity using the site's reporting tools.