Scientists have confirmed that two stimulant drugs banned in the UK appear similar to ecstasy in their immediate effects on the brain.
Selling or possessing mephedrone and methylone, also known as "miaow" and "plant food", was made illegal in 2010.
US and UK researchers have confirmed that their effects on brain chemistry are similar to other amphetamine-related drugs.
A drug charity says use remains widespread, despite the ban.
While there have been studies into the short and longer-term effects of MDMA, or ecstasy, the relative novelty of mephedrone and methylone means much less is known about how they work and whether they are causing damage.
The researchers administered the drugs to live rats while observing changes to a region of the brain called the nucleus accumbens.
The journalNeuropsychopharmacologyreported that, just as with other amphetamines, including ecstasy, as the dose increased, so did the levels of the mood chemicals serotonin and dopamine.
Repeated doses of ecstasy caused a rise in body temperature and more long-lasting changes in brain chemistry, more particularly a lowering of serotonin levels.
This may correspond with a "low" suffered by some ecstasy users in the days after taking the drug.
However, the researchers did not observe these effects to the same degree with mephedrone and methylone.
This did not mean that the drugs were a safer option than ecstasy, the researchers said, adding that their longer-term effects needed further study, as did their addictive qualities.
Harry Shapiro from Drugscope said there were still large numbers of young people using mephedrone in the UK, even though it had been made a controlled substance.
The British Crime Survey results, published in July, suggested that 7.65% of 16- to 24-year-olds interviewed admitted trying cocaine, amphetamines or mephedrone, compared with 5.85% who admitted trying only cocaine or amphetamines.
Mr Shapiro said: "The harms and potential danger with taking drugs such as amphetamines and cocaine are well known, and these substances are related to those drugs.
"There is no evidence that this is a safer option. The real risk comes with mixing different drugs, and if you drink alcohol on top of this it can become a truly toxic mix."