Research suggesting just one Ecstasy tablet could harm humans was based on a laboratory mistake, it has been revealed.
There is controversy over Ecstasy health effects
US experts found that four out of 10 monkeys died or were severely damaged after a small dose of a drug, at first believed to be Ecstasy.
In fact, a far more potent drug had been given to the animals by mistake.
The Johns Hopkins University team were forced to withdraw their paper from eminent research journal Science.
Experts have expressed amazement as to how the flawed research ever managed to get published in such a well-respected publication.
Colin Blakemore, a Professor of Physiology at Oxford University, said that the sheer number of primates left dead or severely damaged already seemed implausible.
He told the BBC: "Whatever we think about the toxicity of Ecstasy, 40% of people using it each weekend do not die."
The original study suggested that even a single episode of Ecstasy use might be enough to produce long-lasting drops in the brain's ability to produce the vital chemical dopamine.
This, they suggested might be enough to trigger conditions such as Parkinson's Disease.
The doses used on the monkeys, they said, were similar to those used by clubbers, Two of the monkeys died after drug treatment, and two could not continue in the trial due to severe brain damage.
The problem with the study came to light when the researchers, led by Professor George Ricaurte, tried to repeat it using Ecstasy in tablet form rather than in the form of an injection.
The results achieved bore no relation to the earlier findings.
In his retraction, published on the journal's website, Professor Ricaurte admitted that their Ecstasy sample had arrived at the laboratory in the same package as another, more potent form of amphetamine.
There had been a mix-up between the two, perhaps due to a labelling error, and the wrong drug had been given to the monkeys instead of Ecstasy.
Tests on brains taken from the monkeys which died confirmed the mistake.
However, Dr Ricaurte said: "This apparent labelling error does not call into question the results of multiple previous studies demonstrating the neurotoxic potential of MDMA (Ecstasy) in various animal species."
Professor Blakemore said that the error was likely to damage the credibility of other scientists carrying out perfectly valid experiments on the long-term effects of drugs such as Ecstasy.
He told the BBC: "It degrades respect for science and I think will have a very dangerous and damaging effect on the attitudes of young people towards scientific evidence and advice about drugs."
He said he was unsure how the normally-rigourous "peer-reviewing" procedure - in which other leading scientists are asked to look over research papers prior to publication looking for mistakes - had failed in this instance.