The drug mephedrone, banned almost a year ago, is still easily available to buy on the internet, the BBC has found.
Mephedrone became a class B drug, the same as speed or cannabis, last April.
But despite the ban and the risk of up to 14 years in prison for supplying it, dealers are still offering large amounts of the drug on websites.
A BBC Radio 5 live investigation found websites offering "designer drugs" including mephedrone, with some even offering free samples to new customers.
After the ban was introduced, some websites closed down while others rebranded themselves as selling compounds they called Research Chemicals - but are actually drugs with names like Benzo Fury, Jolly Bomb Caps and Green Genie Kryptonite.
So far these new compounds have not been made illegal. Meanwhile drug dealers are also moving into the supply of mephedrone in the hope of offering casual users supplies of more addictive drugs like cocaine.
Chinese websites, the source of most compound drugs, offer one kilogram of mephedrone for £1,600. Once mixed with glucose to bulk it out, it could make a drug dealer almost 20 times that amount on the UK's streets.
One 38-year-old user, from the north-west of England, told the BBC: "I can still get it on the street but the quality's not very good.
"There are a lot of drugs for sale on forums, though. It can take you a bit of time to find a good source, but in the end you will find one.
"I know, personally, of one man who sells weed and speed and he's started selling mephedrone because he'll make more money.
"A lad who used to sell a gram of cocaine will now sell a gram of mephedrone. If I can't get any, I'll have the cocaine instead."
A survey in the March edition of the dance and clubbing magazine Mixmag spoke to 2,500 clubbers. Of those who said they'd used mephedrone, 75% had done so since the ban.
Users said they and their friends had concerns about mephedrone, as little was known about it and research into its side effects was limited.
Drugs advice charity Drugscope said users were now its only source of information about the drug.
It said they were aware of users' "reviews" of their experiences posted on forums, detailing what cocktail of drugs they have taken and its effects.
Mephedrone, also known as M-Cat, was banned after being blamed for a series of deaths. However, it later emerged that a number of deaths were linked to other forms of drug abuse.
The patterns of its usage though concerned drugs experts, as it was seen as particularly attractive to young users who had not come into contact with other drugs before.
In 2008 Israel became the first country to ban the chemical, said to give users a similar high to amphetamines or cocaine.