Could Ecstasy, LSD and magic mushrooms one day be legitimate prescription medicines? It sounds unlikely, but doctors and researchers in the US and across Europe believe it is possible and that new science will prove the case.

Second chances are rare in science. In the Fifties and Sixties, hallucinogenic drugs, such as LSD, were hailed as the magic bullet to everything from alcoholism to migraine. But they became caught in the crossfire of the cultural wars of the times. Western politicians banned the use of psychedelics in research once they started to be used recreationally, and became associated with flower-power and the counter culture. The drugs were dangerous; the science was flawed; the researchers biased.

But a comeback has been under way for more than a decade. A new generation of researchers say that psychedelic drugs can treat conditions such as addiction, anxiety, post-traumatic stress disorder and a type of headache called cluster headache.

How it achieves its effect is not clear, but it is thought to affect the action of two moodenhancing brain chemicals, serotonin and dopamine. Proponents say that the drug allows people to open up and express themselves in ways that they otherwise might not be able to. They are also more relaxed and calm, which helps to stop them becoming traumatised again when they revisit painful memories. The drug is neurotoxic at high doses, but the debate continues as to whether a few low to medium doses causes permanent damage.

Supporters argue that any risk is outweighed by the possible benefits for people who have not responded to conventional treatments, and that limited exposure to the drug in moderate doses will not result in addiction or long-term memory problems. Michael Mithoefer, a clinical assistant professor of psychiatry at the Medical University of South Carolina, is finishing a study into MDMA's effect on patients with treatment-resistant post-traumatic stress disorder. He says the preliminary results are promising and that the therapeutic response “warrants our going on to larger studies”.

LSD

The “classic” hallucinogens, such as LSD and psilocybin (the active ingredient in “magic” mushrooms), also affect the serotonin and dopamine systems in the brain. LSD causes hallucinations, commonly known as a “trip”. Researchers believe that it may be useful in treating severe headaches known as cluster headaches. These usually centre around one side of the head, and can occur several times a day for weeks, before stopping for long stretches of up to several months. Scientists believe that these can be treated with a sub-hallucinogenic dose of LSD, which does not cause the wild visual distortions associated with larger doses.

How can a hallucinogen prevent a type of headache? They have a similar chemical structure to serotonin and exert their effects by binding to some of the same receptors as serotonin, a property that is exploited by some mainstream migraine drugs, such as sumatriptan (Imigran) and methysergide.

Andrew Sewell and John Halpern, of McLean Hospital, Harvard Medical School, conducted interviews confirming that LSD and psilocybin were both more effective than conventional drugs at stopping a new cycle of headaches, and that psilocybin was the best drug of all to abort an attack. Halpern is developing full clinical trials. Studies are also under way in Switzerland and the US using LSD or psilocybin as a palliative care agent for patients with anxieties associated with terminal cancer.

KETAMINE

Ketamine is an anaesthetic developed in 1962 for human and veterinary medicine. It works on a wide range of receptors and sites within the brain, with recreational users reporting feelings of euphoria and out-of-body experiences. It is neurotoxic at high doses (at least in rats), but smaller doses could have safer medical benefits, and act as an antidepressant.

In 2006, scientists from the US National Institute of Mental Health injected 17 patients suffering from depression - and who had failed at least six previous drug treatments - with either a low dose of ketamine or a placebo. More than two thirds responded favourably to the drug within a day. However, its psychedelic effects may have to be smoothed out before it can be used therapeutically.

CANNABIS

Users say that cannabis makes them feel relaxed and congenial. It is also known to increase appetite. The drug, or its chemical derivatives (cannabinoids), is used in the US as an appetite stimulant for Aids sufferers and chemotherapy patients.

The cannabis-based medicine Sativex uses fewer psychoactive cannabinoids and is licensed in Canada as an under-the-tongue analgesic spray for patients suffering from multiple sclerosis and advanced cancer. It is also available in Spain and the UK on a case-by-case basis. Researchers are investigating the drug as a potential treatment for conditions such as glaucoma, obesity and diabetes, and as an agent against addiction and hypertension, as revealed recently by scientists at the University of Nottingham.

THE FUTURE?

Not everyone believes that using hallucinogenic drugs for medical purposes will be fruitful, or that it is warranted. “You have to look at research policy within the usual rules without giving way to passion or modern fashions,” says Griffith Edwards, the co-founder of the National Addiction Centre.

He says that the risk to the individual of experiencing drug-induced negative effects must be considered. It may be that a new generation of psychotherapists are viewing the past with kaleidoscope eyes, and that the medical benefits may be a mirage based on bad science in the past when risks were under-reported and follow-ups inadequate.

While scientists and medics do not dispute the catastrophic effects that these drugs can have on physical and mental health when taken recreationally, the pace of research into the medical benefits of such substances, when taken in a controlled setting, shows no signs of slowing down.