The charity said the average strength of pills tested last year was “around 140mg”.
This has risen to 180mg this year, with one in ten drugs tested being above 250mg in strength, it added.
Katy said one of the most important findings during its tests was the wide variation in pill strengths.
“It’s important to remember that even if a drug looks the same, it doesn’t mean that it is the same,” she said.
“It may not be what has been previously taken, previously sold to you.”
Katy told Newsbeat that younger and less experienced users were the ones at most risk from taking a high-strength pill without realising.
“I think it can sometimes be thought that a pill is a single dose,” she said.
“Therefore, when someone is considering taking MDMA pills, it’s really important that one pill isn’t considered to be one dose.”
She said it was important for information to be available over festival season because the drug market constantly changes, and testing helps to keep people up to date.
