Twitter and Instagram have been criticised by a British MP for failing to remove posts advertising Xanax.
There is evidence the anti-anxiety medication is increasingly being used recreationally by young people, some of whom have needed hospital treatment.
Xanax’s manufacturer Pfizer said anyone buying it on social media will be buying fakes.
Twitter said the adverts were organic content created by users rather than being official advertising.
Bambos Charalambous, the Labour MP for Enfield Southgate in London, raised concerns about the drug in parliament. He said: “I’m very concerned that accounts are still up after being reported.
“I think social media companies need to take greater and swifter action to stop these dealers from selling Xanax online.”
In January, Charalambous told the Commons about the 14-year-old daughter of a constituent who ended up in temporary foster care and was expelled from school because of her use of Xanax.
The BBC found that while Facebook was quick to take down posts advertising and promoting Xanax, Twitter failed to remove any of 16 posts and pages reported to it as part of this investigation until contacted for comment.
These were posts promoting the drug created by Twitter’s users, rather than being official advertising.
Instagram took seven of 10 posts reported to it down within two weeks, but one post remained active when the BBC approached it for comment.