At least 20 people were hospitalised during Future Music Festival yesterday.
St John Ambulance sent 20 ambulances to the Arena Joondalup where drugs and alcohol were the biggest issues.
A SJA spokesman said a "fast track" triage was set up at Joondalup Hospital to deal with the influx of admissions from the festival.
Police arrested 16 people and charged another 21 by summons. Twenty five of the 56 charged were for possessing prohibited drugs, while another six were for possessing prohibited drugs with intent to sell supply.
Police also issued 16 drug infringements and 17 move on notices, with Six of those people arrested after breaching the move on notice.