POTENTIALLY lethal legal highs were yesterday banned but an Oxford charity was warned of continued risks as the drugs could "go underground".

The chemicals, designed to mimic the effects of illegal drugs such as cannabis and cocaine, were previously legal to buy from shops but are now prohibited under the Psychoactive Substances Act.

Staff at the MYOX4 addiction hub in Blackbird Leys have trained some 50 frontline staff in Oxford on how to combat the issue and ensure people get help.

Manager DeeDee Wallace, who toured the estate with volunteers yesterday giving out information, warned that over the next few weeks the problem could grow more severe. She said: "I don't have a crystal ball, but it would be naive to think a blanket ban is going to make the problem disappear.

"Just after the law change they may be stronger, the packaging may be different and they may even be less safe. It's really vulnerable groups that are the most at risk."

New psychoactive substances (NPS) such as Spice and Black Mamba can be stronger and more dangerous than typical street drugs.

Emergency services teams are also less equipped to deal with an NPS overdose, as – unlike traditional opiates – there is no 'safe shot' that reliably can be used to treat it.

Miss Wallace added: "There's no control on synthetic cannabis. It could be pot pourri sprayed with chemicals. Far from making people feel relaxed, it's quite psychoactive."

An Oxford man about to complete a 12-step recovery programme with MYOX4 said he had once lived in shared accommodation with a man addicted to Spice – a synthetic version of cannabis.

He said: "It affected him so badly he would sleep sitting up; people would go into his room and take money from his pocket. It's a complete wipeout.

"I tried it myself once or twice and didn't like it. But I can see the appeal; the overall aim is to get obliterated."

At present there are no establishments officially trading as "head shops" – which sold the legal highs – in Oxford, and several former NPS sellers in the city have got rid of their stock.

Former retailer Red Eye off Cowley Road was closed by Oxford City Council a year ago and has rebranded as a skater shop selling only cigarette paraphernalia.

An employee said: "Everything has shut down now but it's for the best. I don't want the business of the people that want these things. We still get asked on a daily basis."