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Brain scans of those using the drug - known chemically as MDMA - have shown damage to specific nerves in the brain.

The damage could cause depression, anxiety, memory disturbance and psychiatric disorders.

The drug is popular at raves

Ecstasy is regularly taken by up to two million young people in the UK.

The nerves it affects are those which release serotonin, which carries messages between nerves.

Serotonin, otherwise known as 5-HT, is thought to play a role in regulating mood, memory, perception of pain, sleep, appetite and libido.

Dr George Ricaurte, a brain scientist at Johns Hopkins University in Maryland, and Dr Una McCann, of the US National Institute of Mental Health, led the research. They published their findings in The Lancet medical journal.

Long suspicions

Dr Ricaurte said: "We had long suspected MDMA was dangerous, based on our earlier studies in primates that showed nerve damage at doses similar to those taken by recreational drug users.

"But this is the first time we've been able to examine the actual serotonin-producing nerve cells directly in the brain."

Dr McCann and her team injected 14 former heavy users of MDMA with radioactive material which attaches itself to serotonin transporter molecules.

They also studied 15 people who had never used MDMA.

Brain scans

When the researchers used a brain-scan technique called positron emission tomography (PET) they found the MDMA users had far fewer serotonin transporters than the other 15 subjects.

The more the subjects had used the drug - 200 times or more in some cases - the greater the loss of transporters.

The kind of damage they observed can lead to lower levels of serotonin in the brain.

The changes were similar to those found in PET scans of animals with MDMA-induced brain damage, which can be long-lasting and, in some parts of the brain, permanent.

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Although some of the Ecstasy users had not taken the drug for several years there was no evidence long abstinence from the drug significantly improved their scans.

Writing in The Lancet, Dr McCann said: "Our data suggest that people who use MDMA as a recreational drug may unwittingly be putting themselves at risk of developing brain 5-HT neural injury."

Long-term risks

The Health Education Authority (HEA) said the findings added to a growing body of evidence suggesting Ecstasy use could cause long-term damage.

Hannah Cinamon, manager of the HEA's drugs programme, said: "We hope this news will make people consider the implications - and certainly the long-term implications - of taking Ecstasy.

"For some time we've highlighted the risk of brain injury as well as the risks of short-term fatigue and periods of depression which can be experienced immediately after use."

She said people who considered using the drug must not forget the associated health risks.