Drug safety organisation The Loop has issued a warning about yellow 'Super Mario' pills containing N-ethylpentylone.
One was tested at Boardmasters in Cornwall at the weekend, with The Loop saying the substance can cause paranoia and insomnia.
The Loop also said N-Ethylpentylone was detected in drugs sold as MDMA at Bestival, while experts have outlined that it's three times as strong as MDMA, which can cause users to take more.
N-Ethylpentylone, which can also cause increased body temperature, anxiety and agitation, has also been in circulation in New Zealand.
Be sure to read this and watch the video below for information about safer MDMA and ecstasy use.
Dave Turner is Mixmag's Digital News Editor, follow him on Twitter