The government agency responsible for drug prevention has said it is concerned with an apparent rise in the number of ecstasy-related deaths.
It is feared some tablets currently being sold as ecstasy actually contain the Class A drug PMA.
Hospitals have been sent alerts about the effects of it, which can be stronger than MDMA (ecstasy).
In 2012, there were at least 10 UK fatalities where PMA contributed towards or caused the death.
The figures, seen by Newsbeat, show in 2011, there were at least four deaths involving the drug, whilst in 2010, there were none.
Rosanna O'Connor, director of alcohol and drugs for Public Health England, said she'd been alerted to PMA in ecstasy tablets in recent months.
"The actual make-up of what people think they're buying, when they're buying ecstasy tablets, changes all the time and this particular phenomena around PMA is a very recent one.
"It looks like a very concerning rise in the number of deaths from these types of drugs."
Club drug clinic
Dr Owen Bowden-Jones is consultant psychiatrist at the Club Drug Clinic, based at the Chelsea & Westminster Hospital in London.
"We've seen a number of people using PMA. One of the problems with PMA is the time it takes for the effect to come on is a bit longer than MDMA," he said.
"People will take a pill thinking it's MDMA and then go, well it's not worked, so they'll take another one and what they're actually doing is double dosing.
"What we understand is the the number of deaths from PMA appear to be higher than MDMA, despite many more taking MDMA. The suggestion is that PMA is more dangerous."
There have been a string of deaths linked to ecstasy-type pills recently which led to police forces around the country issuing warnings about batches of fake tablets.
The street names for PMA can often be the same as those for MDMA, with monikers such as green rolex, Dr Death or pink ecstasy.
'Skin was trying to burst'
One woman, who asked to remain anonymous, told Newsbeat about the last few times she'd taken what she thought was MDMA.
"It didn't feel nice. You didn't feel warm, you didn't feel comfortable," she said.
"You just felt annoyed and when you tried to go to sleep I felt like someone had stuck hot air in me and my skin was trying to burst."
Without testing it's hard to say what she took but some of the described side effects point to PMA.
In recent weeks, the UK Department of Health, the Chief Medical Officers in Wales and Northern Ireland and the Scottish Government have all alerted hospitals and medical teams to the current threat of fake ecstasy tablets and PMA.
One suggestion of PMA's recent prominence is that the main precursor chemical to it, anethole, is currently easier to get hold of than the precursor to MDMA, safrole but there could be other reasons.
Crime Prevention Minister Jeremy Browne said: "Drugs ruin lives and cause misery to families and communities. PMA is a Class A drug because it is dangerous.''
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