Urgent warnings have been issued about purple and pink 'skype' ecstasy pills available at this weekend's Parklife festival, in Manchester.
Drug awareness and testing charity The Loop shared an image of a tablet on Twitter on Saturday night.
The pills - said to contain a very high strength of MDMA - are embossed with the word 'skype'.
One side is purple and the other pink, the Manchester Evening News reports.
The Loop said the pills were tested at the two-day festival at Heaton Park and have been 'linked to welfare cases'.
Anyone feeling unwell was urged to seek urgent medical help.
Reports suggested the pills were the same shape and logo as blue and white tablets found in circulation two years ago.
The Loop said on Twitter: "Multiple purple and pink 'skype' pills.
"Tested today at Parklife and linked to welfare cases.
"Variable and high strength 250 - 300mg MDMA.
"Take care and seek medical help if unwell."
300mg of MDMA is understood to be more than three times the usual amount found in ecstasy pills.
The Loop's tweet was re-tweeted by the official Parklife Twitter account.
Police meanwhile revealed that so far, a total of 18 arrests have been made around Parklife.
Of those, 14 arrests were made on suspicion of possession with intent to supply drugs.
GMP said on Facebook that a number of these arrests related to nitrous oxide canisters.
One arrest was for assault, another for disorder and another for fraud.
Police also made an arrest for failing to appear in court.
The festival is expected to attract 80,000 people each day this weekend.
Parklife boss Sacha Lord issued a drugs warning ahead of the festival and urged all those at Parklife to look after each other.
Mr Lord urged festival-goers to 'party sensibly and pace yourself'.
He said: "You've paid for your ticket and waited all this time to party with your friends and see your favourite acts.
"There's 80,000 of you in a park all there for one reason, to have the time of your lives and enjoy the music.
"Don't overdo it. Party. But party sensibly. Pace yourselves and enjoy the whole weekend. Look after each other."
Police said there had so far been no reports of anyone falling ill.
