A Melbourne Girls Grammar student has been expelled and two others suspended from the exclusive school after they were caught with drugs, reportedly including ecstasy, at a year 12 formal.

The trio was kicked out of the event at Albert Park on Friday night after venue security found students with "illicit substances" and notified school staff, the school's principal Catherine Mission said.

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It has been reported one girl was found with ecstasy, marijuana and alcohol and another was caught with a "significant" number of pills, but the school has not confirmed what drugs were uncovered.