Two young people were taken to hospital during a police operation to tackle anti-social behaviour in West Kirby.
A dispersal zone is in place until midday on Saturday.
Officers say teenagers gathered in the town and at Cubbins Green last night to mark the end of exams.
On Twitter, Merseyside Police said: “On the whole, a well behaved group.
“A few intoxicated teenagers needed to be collected early by parents and one was taken to hospital.
“One young lad assaulted and taken to hospital with head wound.
“We did seize a large number of nitrous oxide capsules.
“We hope they enjoyed their celebrations but maybe they could come back in the morning and clear up their mess.”