Facebook is considering a change to its rules which could allow its users to promote and sell cannabis products for the first time.

The social network is mulling whether to relax its policy on "regulated goods", which currently forbids all discussion of buying and selling the drug.

That could allow legitimate medical and recreational cannabis vendors in places where the drug is legal to market their products, list their prices and encourage people to contact them in order to buy them.

But the idea also raises questions about how Facebook would stop such activity from spreading to Britain, where cannabis remains a class B drug, and how it would prevent it being advertised to under-age users.

"Our policies at the moment do not allow for the sale of marijuana on the platform," said an internal presentation given at the company's moderation policy forum last week, which the Telegraph attended.

"We want to consider whether we can loosen this restriction, especially in relation to medical marijuana, legal marijuana and brick and mortar stores."

Any proposed change would only apply to ordinary Facebook posts, and not to paid adverts or to Facebook's online marketplace, where cannabis will remain off-limits.