Ecstasy is becoming popular again in the European Union, according to a new report on drugs.
With online sales and targeted marketing, there are signs that the drug is resurfacing among a new generation of users, the 2016 European Drug Report has found.
According to the report by European Monitoring Centre for Drugs and Drug Addiction (EMCDDA), MDMA - also known as ecstasy - has returned as "a common stimulant of choice for young people".
Ecstasy first established itself in the illegal drug market in the 1990s, but its use declined at the end of the last decade - mainly due to poor drug quality and adulteration.
Officials are concerned about a "dramatic increase" in the potency of some new ecstasy tablets, Paul Griffiths, EMCDDA's scientific director, said in a news conference.
Also, young ecstasy users may be "more naive" about the potentially fatal risks of overheating and dehydration when taking ecstasy.
The report found that 2.1 million people aged 15 to 34 had taken ecstasy in the last year - 300,000 more than was first estimated.
Griffiths said producers and traffickers are using "sophisticated marketing techniques" to sell more ecstasy.
They include tablets that glow in the dark and drugs manufactured for specific events - such as festivals. It is also believed that the use of unique logos may have played a part in the rising number of consumers.
Authorities believe most ecstasy in the EU is produced in or around the Netherlands.
"The MDMA content of tablets has increased since 2010 and is now at an all-time high whilst prices appear to have remained relatively stable," the report said.
Despite ecstasy's return its use is still dwarfed by the popularity of cannabis. That remains the EU's biggest-selling drug in money terms with an estimated annual retail value of 9.3 billion euros (£7bn) in 2013, the last year for which full figures are available.
Agency figures reveal the retail market for illicit drugs in the EU was at least 24 billion euros (£18bn) in 2013.
Heroin sales are estimated to be the second highest, at 6.8 billion euros (£5.1bn), followed by cocaine at 5.7 billion euros (£4.4bn). Sales of MDMA are believed to total almost 700 million euros (£534m).
Cannabis offences, mostly involving use or possession for personal use, account for close to three-quarters of all drug-related offences in the EU.
The agency said online drug sales appear to be growing, representing an "important new challenge for drug policy".