The seven men and two women were taken ill in Liverpool city centre on Saturday night.
Police confirmed the substance is believed to have contained mephedrone — also known as meow-meow.
Samples of the drug have been sent for forensic analysis. All nine were treated and later released from hospital.
Mephedrone first appeared on the British drugs scene in 2009 and its popularity grew rapidly as it was sold as a legal high.
A number of deaths were linked to its use and it was banned last year.