Paramedics treated the woman, aged in her 30s, on Friday at the Flemington Showgrounds event.
She was taken to the Royal Melbourne Hospital in a critical condition.
Another woman in her late teens also had to be hospitalised for suspected substance use, and was in a stable condition.
It comes after nine people were hospitalised on January 6 for drug overdoses at the Hardmission Festival in Melbourne.
Victoria's health department on Friday confirmed they had used MDMA at last week's music event.
Some patrons were also exposed to other drugs including PMMA, synthetic cathinones and methamphetamine.
"Consuming these substances at a hot, humid music event will increase the risk of life-threatening hyperthermia," the department said.
"If you're at a festival, seek out the first aid service. Their assistance can be the difference between life and death."
Despite recent overdoses, the Victorian government has no plans for pill testing at music festivals. (Lukas Coch/AAP PHOTOS)
The Victorian Greens have once again urged the state government to introduce pill testing to keep young people safe.
"Every day the Victorian Labor government refuses to listen to expert health advice and back pill testing is another day a young person is at risk of overdose or drug-related death," acting party leader Aiv Puglielli said.
"Sniffer dogs will not save lives. Tough talk from cops and politicians will not save lives. Pill testing will."
The state government confirmed earlier this week it had no plans to introduce pill testing, and was instead focused on harm minimisation.
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