There are isolated reports of quite damaging effects on learning and memory from taking just a few tablets

Professor John Gruzelier

The university has still to decide whether the trials will actually take place.

If they do, they will be designed to find out whether traumatised patients respond better to psychological therapy after taking ecstasy.

The FDA decision was announced by a group called the Multidisciplinary Association for Psychedelic Studies (MSPS) which was campaigned for years for funding to study the potential of Ecstasy as a therapeutic drug.

The organisation hopes to develop Ecstasy into a prescription drug.

Amphetamine

Ecstasy is an amphetamine that has both stimulant and hallucinogenic effects in humans.

The drug is popular among adolescents and young adults who attend "rave" dance parties, clubs and rock concerts.

However, evidence is mounting that it may have a serious long-term impact on mental health.

Rick Doblin, MSPS president and founder, believes the drug could help people with post-traumatic stress because it enabled them to "let go of fear" and emotionally work through an upsetting experience.

No decision on whether the trial will go ahead is expected before January.

Post traumatic stress disorder can strike after military combat, rapes or serious accidents.

Patients suffer flashbacks, feel emotionally numb or become irritable or easily startled.

Professor John Gruzelier, an expert in post traumatic stress disorder from Imperial College, London, told BBC News Online that there were better ways to treat the condition.

He said: "Hypnosis has been very effective, and is a tried and tested method.

"This is a very novel and unusual application for Ecstasy.

"One off use of Ecstasy is different from the sort of contamination we have found in heavy users.

"But there are isolated reports of quite damaging effects on learning and memory from taking just a few tablets."