The dance drug Ecstasy is set to be used in a medical trial involving patients with post-traumatic stress.
Ecstasy remains an illegal drug
Final ethical approval has been given for the tests, based at the University of South Carolina in the US.
Ecstasy, also known as MDMA, was originally created as a slimming aid - and was made illegal after an upsurge in recreational use in the 1980s.
The trial will test the effects of the drug on traumatised crime victims, and is expected to start in the New Year.
The use of MDMA therapeutically is controversial - many experts believe there already exist better ways of helping people with post-traumatic stress.
Studies of the long-term effects of taking the drug also suggest there may be health risks, although this is not fully proven.
The drug works by boosting the levels of the chemical serotonin in the brain. Serotonin is important in the regulation of mood, and users often report a feeling of calmness, alongside warmth and empathy towards others.
The South Carolina study has been on the drawing board for years.
Original approval from the US Food and Drug Administration (FDA) was given in November 2001, but there followed a series of rejection from boards of ethics linked to US universities.
Dr Rick Doblin, who is leading the study, told The Guardian: "What we'd like to do is develop MDMA into a prescription medicine.
"Of course there are risks, but I do believe the risks are manageable."
He believes the effect of Ecstasy would be beneficial for people suffering extreme stress disorders because it might promote "cartharsis" - a purging or release of emotions which the patient finds it hard to talk about during normal counselling.
The trial will use a combination of the drug and organised therapy sessions.
The intended dose is approximately the same as the amount of the drug found in a typical ecstasy tablet sold illegally.
MDMA was used unofficially as an adjunct to counselling sessions as recently as the 1970s, but fell out of favour at the same time that recreational use was becoming popular.
Professor John Henry, at Imperial College London, who carries out research into the toxic effects of recreational drugs, said that there was no reason to dismiss the idea that MDMA might be medically useful simply because it was used illegally.
He said: "We have medical heroin, medical cocaine - and now we could have medical ecstasy.
"We know that it can kill you - but used in a controlled laboratory or a clinical setting, the risks would be minimal.
"Over the long term, it can interfere with the ability to incorporate new memories, but if you're taking it once or twice, it shouldn't be a problem."