Two men, aged 21 and 25, and two women, aged 30 and 31, needed emergency treatment after falling ill at Saturday night’s event.
Police were called to the venue on Lowfields Road in Beeston shortly after midnight by paramedics who said they believed the revellers had overdosed on Gamma Hydroxybutyrate (GHB).
The party-goers were taken to hospital and released after treatment.
A 32-year-old man was arrested on suspicion of supplying controlled drugs and is today in custody.
Leeds District CID’s Det Insp Jaz Khan said: “We would urge anyone who has recently purchased this substance in the Leeds area to throw it away, as it is possible there may be a contaminated batch in circulation.
“We would also ask anyone who attended the event at the Pavilion, who may have information about anyone selling controlled substances in the area last night, to contact us on 101 or make a report anonymously via the independent charity Crimestoppers on 0800 555111.”