New Scientist magazine says that while there is little doubt that the drug can be harmful, some studies suggesting a serious impact on the brain cannot be trusted.

All the papers have very significant scientific limitations that make me uneasy

Marc Laruelle

Central to the magazine's argument are question marks over the validity of brain scans which researchers have said show that ecstasy damages production of a vital brain chemical called serotonin.

The scans purportedly provided evidence that the drug destroyed nerve cells that specialise in serotonin production.

US researchers used a radioactive chemical to show up serotonin activity in the brain.

Scans showed that the brains of ecstasy users glowed less - suggesting that the drug had reduced serotonin production.

Pictures of the scans were used in public information campaigns, and in the US strongly influenced the introduction of harsher penalties for ecstasy offences.

Methodology flaws

But two independent experts told New Scientist there was a key flaw - the way brains reacted to this kind of scan, known as PET, varied enormously with or without ecstasy.

We know that ecstasy can kill and does kill unpredictably

Home Office

Some "healthy" brains glowed up to 40 times brighter than others, and even a number of ecstasy users' brains outshone ecstasy-free brains by factors of 10 or more.

Similar criticisms applied to another study by Dutch scientists which indicated that women might be more susceptible than men to brain damage from ecstasy.

Stephen Kish, a neuropathologist at the Center for Addiction and Health in Toronto, told the magazine: "There are no holes in the brains of ecstasy users.

"And if anyone wants a straightforward answer to whether ecstasy causes any brain damage, it's impossible to get one from these papers."

Marc Laruelle, an expert on brain scanning at Columbia University, New York City, said: "All the papers have very significant scientific limitations that make me uneasy."

He pointed out that the chemical probes used in ecstasy brain scans do not always stick solely to serotonin transporters.

Mental agility

Similar uncertainty surrounds evidence that ecstasy impairs mental performance, according to New Scientist.

In the majority of tests of mental agility, ecstasy users performed as well as non-users.

Ecstasy was classified a Class A drug in the UK in 1977, on the recommendation of the Advisory Council on the Misuse of Drugs.

In 1996 the independent advisory body convened a special meeting to discuss ecstasy, following a number of deaths.

It concluded that ecstasy posed a "very real risk" of fits, serious mental disturbance and death.

A Home Office spokesman said: "The Advisory Council on the Misuse of Drugs will of course be keeping abreast of current research on ecstasy, and if necessary undertake a further review of the drug.

"But on the basis of their recommendations so far, we know that ecstasy can kill and does kill unpredictably, and therefore there are no plans to change its classification as a Class A drug."