Three leading British mental health scientists have urged the United Kingdom government to loosen restrictions on the psychedelic compound psilocybin so that researchers can explore its use as a medication for depression and other disorders.

King's College psychiatrists Allan Young and Simon Wessely and University College London neuroscientist Karl Friston have written to Health Secretary Sajid Javid about the potential merits of psilocybin, which is the active ingredient in magic mushrooms.

The psychedelic compound is currently classified within Schedule 1 of the Misuse of Drugs Act, which includes highly controlled drugs not deemed to have therapeutic value.

In the letter, which was posted online on Tuesday, the specialists said that health authorities should assess psilocybin with a view to "rescheduling this promising medicine and experimentally useful compound at the earliest opportunity".

Trials involving Schedule 1 drugs have extended timeframes and increased costs, since researchers must obtain licenses from the Home Office.

James Rucker, who is head of the psychedelic trials group at King's College London, said that small-scale clinical trials indicate that psilocybin is an effective treatment for a range of mental health problems, including treatment-resistant depression, anxiety disorders, and post-traumatic stress disorder.

"This is the most promising new treatment for a generation," Rucker said in a campaign statement for the Conservative Drug Policy Reform Group, or CDPRG. "In the face of Schedule 1 restrictions, further clinical development work on psilocybin is almost impossible. Schedule 1 imposes bureaucratic and practical restrictions that make clinical trials with it much more expensive than they need to be, and much too difficult for research institutions to undertake."

Rucker said that psilocybin showed great promise as a treatment for depression in the mid-20th century, before the compound became caught up in the United States-led war on drugs, and the UK made it illegal for doctors to prescribe psychedelics and hallucinogens in 1971.

Today, commonly-used treatments including anti-psychotics, lithium, and electro-convulsive therapy do not work for many patients, Rucker said.

"Modern pharmaceutical companies have failed to develop treatments which are any better than Prozac, which has now been on the market for over 30 years," he said. "Schedule 1 restrictions are not necessary as psilocybin is not dangerous and it is not addictive."

Conservative member of Parliament Crispin Blunt, who is chairman of the CDPRG, said: "Britain has got to unlock the potential here, for our own bioscience industry, for our own psychotherapists to be able to effectively treat British patients, and if Britain is serious about leading in the areas of medicine and bioscience, we need to move our regulatory regime to enable safe application of these revolutionary new medicines," Blunt said in the campaign statement.