In the first-ever US referendum on magic mushrooms, 50.6 per cent of voters in Denver, Colorado voted to bar officials from “spending resources to impose criminal penalties” for the use or possession of the psychedelic drug.

Though magic mushrooms will remain illegal under federal law and selling them will remain a felony, officials will be effectively prevented from taking forward arrests or prosecutions.

Hallucinogenic mushrooms remain illegal in Denver and the rest of Colorado, and selling them will still be a felony. They also remain a Schedule I controlled substance under federal law.

The ballot initiative passed in spite of strong opposition from Denver Mayor Michael Hancock and Denver District Attorney Beth McCann, as well as the federal government.

Ms McCann told the Washington Post that she thought the proposal was coming too soon after the legalisation of cannabis in Colorado in 2014.

She said: “We’re still figuring out marijuana, and even though things are going well so far, we’re still measuring the impacts on the people of Denver.”

However, campaign group Decriminalise Denver argued that “no-one should go to jail, lose their children, lose their job, and lose their citizen’s rights for using a mushroom”.

The proposal put to voters included the establishment of a review panel to analyse the public safety, administrative, fiscal and health impacts of the decriminalization of magic mushrooms.