Taking a psychedelic drug extracted from "magic mushrooms" may provide lasting benefits for people tormented by incurable depression, new research suggests.
A small pilot trial of 12 patients with treatment-resistant depression - which in some cases had persisted for decades - found that every participant experienced a reduction in symptoms a week after taking the strictly controlled Class A drug psilocybin.
Eight of the 12 (67%) achieved full remission after a week and were temporarily liberated from their demons.
Three months after swallowing psilocybin capsules, seven patients continued to show an improvement and of these five remained depression-free.
However, the treatment involved a high dose of psilocybin, equivalent to eating several magic mushrooms.
All the patients had to "trip" on the drug, just as if they were taking it recreationally to experience its hallucinogenic effects, and all received psychological support to help them cope.
Volunteers were carefully screened to exclude anyone with a history of suicide attempts, psychosis or drug dependence.
While anxiety affected every patient, the treatment produced few adverse side effects.
Some patients reported confusion, nausea and headaches, and two suffered a brief episode of mild paranoia.
Lead scientist Dr Robin Carhart-Harris, from Imperial College London, said: "These experiences with psilocybin can be incredibly profound.
"Sometimes people have what they describe as mystical or spiritual-type experiences - that's not uncommon, particularly with the high dose.
"So it's important that we provide psychological support afterwards.
"We didn't see anything unexpected and the adverse effects were mostly things that we predicted and were relatively mild.
"Nevertheless, the limitation of this treatment is the acute experience itself. It can be... psychologically challenging."
He pointed out that all the patients taking part in the study had been diagnosed with moderate to severe depression and had previously failed to respond to two different types of antidepressant drug treatment.
On average, the participants, who ranged in age from 30 to 64, had been suffering from depression for 18 years. One man of 40 had been ill with depression for 25 years and a woman of 43 had struggled for 30 years.
"This isn't a magic cure, but even so the effects at this stage do look promising," said Dr Carhart-Harris.
The patients received two capsules of Home Office-licensed psilocybin one week apart.
The first, given as a safety precaution, contained a low 10mg dose of the drug and the second a high 25mg dose.
Patients were assessed one day after the first dose and then at one, two, three and five weeks, and three months, after the second dose.
Because the trial was not randomly controlled or blinded - all the patients knew what they were taking - the reliability of the results is open to question.
Dr Carhart-Harris acknowledged that participants may have been influenced by attempts to help them relax, such as playing music, or experienced a therapeutic "placebo effect".
He added: "New treatments are urgently needed, and our study shows that psilocybin is a promising area of future research.
"The results are encouraging and we now need larger trials to understand whether the effects we saw in this study translate into long-term benefits, and to study how psilocybin compares to other current treatments."
The scientists, whose findings are reported in the journal The Lancet Psychiatry, hope to obtain funding for a larger randomly controlled trial which would compare the effects of psilocybin with those of an inactive "dummy" drug or other form of treatment.
One member of the team, former drug tsar Professor David Nutt, hailed the study as a "landmark" but lashed out at the "Kafkaesque" restrictions that made it so difficult to conduct research on psilocybin.
Because of the regulations and red tape, "it cost £1,500 to dose each patient when in any sane world it might have cost £30", said Prof Nutt.
He argued that obstacles in the way of investigating the therapeutic potential of psilocybin could be lifted "overnight" if the Home Secretary reclassified it as a Schedule Two drug, which can be prescribed and supplied by doctors.
"Because it's Schedule One, it's subject to a whole panoply of regulations that make research almost impossible," said Prof Nutt.
Precisely how psilocybin might lift depression remains an unanswered question. Previous brain scan studies suggest that it dismantles a harmful hyperactive neural circuit that causes people to be inward-looking and to dwell on thoughts of failure and inadequacy.
The scientists received a grant of £466,613 from the Medical Research Council (MRC), which was originally supposed to pay for a randomised, placebo-controlled trial involving up to 44 patients. However the pilot study, required to satisfy regulatory requirements, used up all of this funding.
Co-author Amanda Feilding, director of The Beckley Foundation, a research think-tank that investigates the potential medical benefits of psychoactive drugs, said: "It is very exciting that our latest psilocybin study paves the way for a new treatment for depression.
"For the first time in many years, people who were at the end of the road with currently available treatments reported decreased anxiety, increased optimism and an ability to enjoy things.
"This is an unparalleled success and could revolutionise the treatment of depression."
Prof Nutt, director of the Neuropsychopharmacology Unit at Imperial College, was famously sacked from his former job as the Government's chief drug advisor in 2009 after claiming that ecstasy and LSD were less dangerous than alcohol.