Teenagers are buying Xanax on social media to help them cope with exam stress, addiction experts have said.

Grammar school pupils are so stressed by their work that they are taking the drug "on a daily basis," experts warned.

Drugs charity Addaction said children as young as 13 were buying it online, and a BBC investigation found drugs advertised on Instagram and Facebook.

Journalists were able to buy products which the dealers said were Xanax and diazepam.

Both companies said that buying or selling drugs was not allowed on their platforms, and the accounts had been removed.

Neil Coles, who works for the charity with children in Canterbury and the south east, said he was increasingly working with gifted, able children who were using it for self-medication.

"There's a lot of use in grammar schools, a lot in those high-pressure environments.

"It's used as a party drug as well but I'm also seeing it used within the school environment - so children taking a quarter of a bar to alleviate the stress of a school day," he told the Daily Telegraph.

He said the children using it were often "outside of those traditional drug-using cohorts" who would use it recreationally.