We know it has these effects on the brains of monkeys, and human brains are not that different

Professor Valerie Curran

The research is to be presented at the British Psychological Society's London meeting on Tuesday.

Other research teams at the conference suggest that the drug is more likely to have a negative psychological effect on older people, or those who do not drink water as a precaution while taking it.

However, the UCL research is likely to provoke the most debate.

The team, led by Professor Valerie Curran, examined 96 volunteers, who were either current frequent users of the drug, ex-users who had previously taken the drug regularly, or people who had never taken Ecstasy, but had taken other recreational drugs.

All were subjected to tests involving the supply - or lack - of tryptophan, a chemical which is key to the production of seratonin, another chemical known to have profound effects on mood and memory.

It was the ex-users who stood out in the tests, performing much worse when they were deprived of the chemical, and much better when it was given.

Years of use

The researchers pointed out that just because the ex-users appeared to be more vulnerable to this sort of chemical manipulation of the brain, it did not necessarily mean that Ecstasy had created such different conditions.

They said that the differences might have been underlying, and caused them to have an abnormal response to Ecstasy leading them to give it up.

However, as the average length of time the volunteers had been using Ecstasy was measured in years rather than weeks, this is less likely.

But Professor Curran told BBC News Online: "When combined with the animal studies, the evidence is certainly growing that there are long-lasting effects.

"We know it has these effects on the brains of monkeys, and human brains are not that different.

"It's certainly a worrying finding."

Dr Philip Murphy, from Edge Hill College of Higher Education in Lancashire is to present his study of Ecstasy users, which suggested that longer-term users were less likely to experience positive effects from the drug, and more likely to experience negative effects.