Ecstasy use among young Britons is at the highest level for more than a decade, new figures reveal.
One in 20 people aged between 16 and 24 admitted taking the Class A drug in the last year, findings from the Crime Survey for England and Wales show.
The figure for ecstasy use among 16-24-year olds - 5.4% - is the highest since 2003/04 (5.5%), and is up just over a third (38%) year on year compared with 2013/14.
The rise was described as a "statistically significant increase" by experts.
A report released by the Home Office said: "Although the long-term trend in last year ecstasy use among young adults shows many fluctuations, the overall long-term direction before the recent increases was downward. It is too early to say whether the latest estimates show a change in the direction of the trend, or another fluctuation."
However, the study showed that the proportion of young adults who said they had taken drugs in the previous year had dropped sharply over the last decade.
The study also provided one of the first insights into the popularity of new psychoactive substances (NPS) - often referred to as "legal highs" or designer drugs.
It said that overall the prevalence of NPS use among adults aged 16 to 59 was "generally low" compared with established substances such as cannabis, cocaine and ecstasy.
The 2014/15 survey estimated that 0.9% of adults in that age range had used an NPS in the last year - the equivalent of 279,000 people.
Younger adults were more likely to have used the substances, with 2.8% of 16 to 24 year olds - 174,000 people - having taken one in the last year, the study found.
The proportion rises to one in 16 (6.1%) when youngsters were asked if they have tried a legal high at some point in their lifetime.
Around 128,000 young men had taken an NPS in the last year, compared with 47,000 young women, the report said.
One in three adults buy their legal high from a shop (34%) and another third get them from a friend, neighbour or colleague (34%). Only 8% get them from a known dealer and 6% get them from the internet.
Other findings include: Around one in 12 (8.6%) adults aged 16 to 59 had taken an illicit drug in the last year - around 2.8 million people - and one in 5 (19.4%) young adults had taken them, round 1.2 million people. This was similar to last year's proportion but "significantly lower" compared with a decade ago, when it stood at 26.5%.
And around one in 20 adults aged 16 to 59 had taken an illegal drug in the last month and just over a third had done so at some point in their life.