The powerful legal high mephedrone is becoming much more widely used on the British club scene, a survey suggests.
One in three readers of dance magazine Mixmag polled for an academic study has used the powder in the last month.
The results make mephedrone the fourth most popular substance in the survey.
"We were surprised. It's come from nowhere to become very popular," said Dr Adam Winstock from the National Addiction Centre, who led the research.
"For a drug that's been around for a relatively short amount of time, mephedrone has certainly made a big impact on the dance drug scene."
The government has said it is a "priority" to find out more about the dangers of using the stimulant.
Its team of drug advisors has now written to the home secretary warning that substances like mephedrone could have "serious public health implications" and saying it will provide advice "as soon as possible on this important issue".
But a series of resignations from the advisory council linked to the sacking of its then chairman, David Nutt, in November is threatening to hold up the research.
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Mephedrone is usually snorted although it can also be taken in pill form, mixed with a drink or, in rare cases, injected.
It is sold online through dozens of dedicated websites as a "plant food" to get round the Medicines Act, although it has no known use as a fertilizer.
"The fact it is legally obtainable is absolutely no guarantee [of safety]," said Dr Winstock. "At the moment we just don't have the research to know what it does to people in the short term and long term."
Most users describe the effects of mephedrone as a cross between cocaine and ecstasy.
"I've taken it a couple of times in clubs," said 25-year-old Tina from South Wales. "We always get it from the same place and the experience is consistent. It is very similar to ecstasy."
"I have heard of people with horror stories but anyone who takes drugs accepts there can be negative side effects."
The results of the survey were based on an online poll of 2,222 readers of the clubbing magazine Mixmag carried out by researchers at the National Addiction Centre at Kings College, London.
51% of mephedrone users in the study said they suffered from headaches; 43% from heart palpitations; 27% from nausea; and a further 15% from cold or blue fingers.
"The first thing I noticed was that I couldn't urinate at all," said Danny, 24, from Colchester. "My heart was beating really fast and I was sweating badly.
"It's very moreish and you constantly want to re-dose. I ended up buying five grams and went on a two-day bender on it.
"It's a worry because it's probably putting a lot of stress on my heart and other organs. You can definitely develop a habit from doing it."
Other anecdotal reports suggest heavy use can lead to paranoia, hallucinations and serious panic attacks.
Almost nothing is known about the long term effects of taking it.
The government's team of drug advisors is now looking into the dangers and health effects of mephedrone.
A report and series of recommendations are likely to be presented to the home secretary before the summer.
"We want to take a careful look at the evidence and we are doing just that," said Professor Les Iversen, the new interim chairman of the Advisory Council on the Misuse of Drugs (ACMD).
"We suspect that mephedrone and five other compounds in the same family are different versions of classical amphetamines and have all the problems associated with that: hyper excitability, aggression, heart problems and a high liability to dependence and addiction.
"We don't know if this is all true for mephedrone and we need to find out."
But five of the scientists originally working on research for the ACMD resigned last November in a political row following the sacking of then Chairman David Nutt.
Former members claim the council will "struggle" to function over the next few months until new scientists can be appointed.
The home office points to the recent banning of the drug GBL as evidence it is committed to cracking down on legal highs if they pose a "significant threat to health".
"Making substances illegal is only part of the solution," said a spokesperson for the home office.
"It is important to understand that just because a substance is legal, it doesn't mean it's safe to consume.
"Last year we launched an information campaign targeted at clubbers to raise awareness of the dangers of legal highs, including mephedrone, when people try to buy them online."