West Yorkshire Police revealed that there have been reports of dealers selling fake MDMA at recent festivals this summer that has actually turned out to be a substance called N-ethyl Pentylone (NEP).
This is three to four times stronger than normal MDMA.
The Loop, a not-for-profit company that provides drug safety testing, has issued an alert about the drug and said the substance is almost identical to MDMA and is being sold in pill, powder and crystal form.
The 'high' from the drug is said to be much shorter, whilst the negative side effects are much longer.
It can lead to 12 to 48 hours of severe insomnia, paranoia, erratic behaviour and drug-induced psychosis.
Both The Loop and officers have also warned about 'legal highs', stating ghat despite the name, there is no guarantee that it is safe to take or a legal substance.
WYP warned: "Whether it’s claimed to be a legal high or a banned substance, people supplying drugs are more often than not unscrupulous individuals who don’t care about you.
"Aside from the potential effect that anything you take may have on your health and wellbeing, drugs can also have a significant effect on your life and future.
"A conviction for taking or supplying controlled drugs to your friends will impact on your life. This can include travel plans, employment prospects as well as your general reputation.
"Come to the festival and enjoy it but don’t let one bad decision ruin the weekend and jeopardise your future."
Organisers of Leeds Festival have included N-ethyl Pentyloneon a list of substances they know have caused deaths, overdoes, injury and hospitalisations.
Drugs known as Red Heart Pills, Homer Pills, Super Mario Pills, Mastercard, LSB Blotters, Silver Bar, Lewgo, Orange Soundcloud, CEC and Phillip Plein are also on the list.
Organisers of Leeds Festival said that drugs are not tolerated at Leeds Festival.
The website states that drug enforcement laws are as applicable onsite as anywhere else in the UK.
There are stringent security checks on the way into the site.
WYP warned that the staff are adept at finding drug stashes and anyone found with a suspicious substance will be arrested and taken from the site while tests are undertaken to ascertain the exact nature of a powder or tablet.
Last year was a 'record year' for the seizure of illegal drugs at Leeds Festival according to one top police chief.
Despite drugs being illegal, organisers have stated that they want those who do chose to take them to remain as safe as possible.
They said: "We want our festival goers to know above all else that you can come to us for help without fear of getting in trouble at any time.
"Remember if you take drugs and become ill, depressed or concerned, make sure you ask the nearest member of staff to direct you to our Welfare Tent in the Village which is open 24 hours.
"If you or someone you are with has a bad reaction and needs medical help, talk to the nearest member of staff immediately.
"Let the medics know what has been taken. You could save your friend’s life.
"People who are overdosing can go downhill very quickly so don’t delay in seeking help."