People going to the V Festival are being warned they will be searched for drugs before they get into the event.
Police say visitors to Weston Park on the Staffordshire-Shropshire border will be given the chance to dump any illegal substances on entry.
But the Staffordshire force is warning that anyone who fails to do so could be arrested and charged.
Police will also be patrolling with sniffer dogs during the event, which lasts from Friday until Sunday.
Supt Kevin O'Leary said: "We want to make the event as safe as possible and we are determined to stamp out drugs misuse.
"People possessing illegal substances with intent to supply will be stringently dealt with."
Police are reminding that it is still illegal to possess cannabis, despite its recent downgrading to a Class C drug.