Legal highs are becoming a bigger problem than illegal drugs, with many young people wrongly believing they are safe, a drugs worker claims.
Alan Andrews, an ex-heroin addict who runs a Llanelli-based drug intervention centre, said some legal drugs were stronger than illegal counterparts.
He told BBC Wales' Week In Week Out that legal did not mean safe.
The UK government plans to bring in temporary banning orders for legal highs to be tested.
The programme has investigated the issue of legal highs, more than a year after the drug mephedrone, or meow meow, was banned.
Legal highs are substances that are manufactured in a laboratory which do not fall under the current legislation of banned substances under the Misuse of Drugs Act, according to Dr Mohan Da Silva, lead clinician for charity Kaleidoscope Wales.
Undercover recording has found shops breaking the law by selling some of these drugs for human consumption.
Mr Andrews, managing director of Chooselife, said: "It's becoming a bigger problem than illegal drugs because... the message 'legal' means safe, which it's not.
He said some of the legal high drugs "are stronger, more potent than the illegal drugs and it's quite scary".
"There's a generation of young people who are being sold a lie that legal means safe."
Secretly recorded Week In Week Out footage shows a 17-year-old girl being sold a drug called salvia.
She is also sold equipment and shown how to use it to smoke the drug.
Salvia, derived from a Mexican plant, is legal to possess but it is against the law to sell it for human consumption.
John Ramsey, a toxicologist and member of a working group to the Advisory Council on the Misuse of Drugs, said the drugs laws needed to be reviewed.
Mr Ramsey said salvia had not been banned because the fact it was so potent meant very few people took it more than once.
"There has been a lot of talk about whether things are appropriately classified and I think the development of these new compounds at the rate they're being developed probably warrants a second look at how we control all drugs," he said.
Legal highs are not new but there are more of them and there are concerns they are getting more potent.
Last month the monitoring centre which records drug use across Europe said new highs were appearing at an "unprecedented" pace.
Some 41 new substances emerged in 2010, 16 of which were first reported in the UK.
The most high profile has been mephedrone, which has been linked to a number of young people's deaths.
It was banned in April last year but the programme has found it is still being used in Wales, where there have been 100 arrests since the ban.
The UK government is planning to bring in temporary banning orders, to allow time for legal highs to be tested.
The Home Office said: "So-called legal highs can be extremely dangerous and anyone taking them is playing Russian roulette with their health.
"We are building one of the most robust systems in the world to tackle this worrying trend."
Getting High In Wales: Week In Week Out is on Tuesday, 21 June on BBC One Wales at 2235 BST.