A UK trial that could lead to radical "magic mushroom" treatments for depression has been stalled because of "absurd" regulations restricting the use of illegal drugs in research, it is claimed.
Study leader Professor David Nutt, controversially sacked from his role as the British government's chief drug adviser in 2009, argues that "archaic" rules obstructing scientific progress should be abolished.
His team at Imperial College London has uncovered evidence that the hallucinogen psilocybin may combat severe depression which resists conventional treatment.
The problem is that psilocybin is the psychoactive ingredient in so-called "magic mushrooms", and banned as a Class A drug.
Although the Medical Research Council has awarded a £550,000 (€648,86) grant for the trial, Prof Nutt says the study has not yet been able to proceed.
Speaking on the eve of the British Neuroscience Association's Festival of Neuroscience in London, the professor said: "The trial hasn't started yet because the big problem is getting hold of the drug.
"We're not allowed to go and pick the mushrooms any more and finding a company to provide this illegal drug in a way that can be prepared for trial use as yet has proved impossible.
"We are between a rock and a hard place, and that's very unfortunate because if this is an effective treatment, as it may well be for some people, then they are obviously being denied that possibility."
Under the law, academic researchers are not allowed to manufacture their own Class A drugs and must obtain them from external sources.
Companies that could supply the drugs have to go through "regulatory hoops" to obtain the necessary Home Office licence, said Prof Nutt. This could take up to a year and triple the cost, he maintained.
Other major hurdles were the EU guidelines on Good Manufacturing Practice, which sets daunting standards for potential suppliers, and rules on storage.
Only four hospitals in the UK currently have a licence to hold psilocybin, making it difficult to roll the drug out as a prospective treatment, said Prof Nutt.
He added: "The knock-on effect is this profound impairment of research. We are the first people ever to have done a psilocybin study in the UK, but we are still hunting for a company that can manufacture the drug to GMP standards for the clinical trial, even though we've been trying for a year to find one.
"We live in a world of insanity in terms of regulating drugs at present. The whole field is so bogged down by these intransigent regulations, so that even if you have a good idea, you may never get it into the clinic.
"The rules are absurd. They just need to be abolished. There's no rationale to them at all. This is just a historical anomaly that we're chained to."
It is illegal to carry magic mushrooms to a teapot, but paradoxically permissible to "kneel down and eat them fresh from the ground", said Prof Nutt.
He vowed to continue searching for a source of psilocybin, but said he may have to ask the MRC to extend the study's funding period.
His team of researchers discovered that when healthy volunteers are injected with the drug it shuts down a region of the brain known to be over-active in depression.
"We found that, even in normal people, the more that part of the brain was switched off under the influence of the drug, the better they felt two weeks later," he said.
"This is the basis on which we want to run the trial."
Psilocybin targeted a brain circuit called the "default mode network" that appears to cause some people to be locked into a continual cycle of depression.
For the trial, Prof Nutt wants to recruit 60 patients with depression who have failed to respond to two previous treatments. Half will be given a synthetic form of psilocybin and half a "dummy" placebo drug.
Patients will be given a low dose of the drug to start with, working up to higher therapeutic doses. Their condition will be monitored for at least a year.
"What we are trying to do is to tap into the reservoir of under-researched 'illegal' drugs to see if we can find new and beneficial uses for them in people whose lives are often severely affected by illnesses such as depression," said Prof Nutt.
Around 40% of depressed patients fail to respond to initial treatment, and some 10% are currently beyond help, said the professor. It is these untreatable patients who could be offered new hope by psilocybin, he believes.
In 2009 Professor Nutt was asked to step down from his role as chair of the Advisory Council on the Misuse of Drugs after claiming that alcohol and tobacco were more harmful than LSD, ecstasy and cannabis.
He is now president of the British Neuroscience Association and Professor of Neuropsychopharmacology at Imperial College London.