People going to the V Festival in Weston Park this weekend are being warned not to bring drugs with them.
The festival is sold out
Officers say they will be searching revellers as they enter the site on the Staffordshire-Shropshire border.
Police will have what they describe as a mobile drugs laboratory to analyse any substances, and they will also be using sniffer dogs to look for drugs.
Amnesty bins will be provided but people caught with drugs could be put before the next court, police warn.
Officers say all people found with drugs will be arrested.
DNA samples and fingerprints will be taken and kept on record.
Police say they would like to remind people that, although cannabis has been reclassified as a Class C drug, it is still illegal to possess.
Ch Insp Peter Taylor said: "We are working closely with the organisers to ensure that V Festival 2005 is a safe and enjoyable experience for everyone, including festival-goers and members of the local community.
"Drug dealing and misuse will not be tolerated and people possessing drugs with intent to supply will be dealt with firmly."
The event runs from Friday to Sunday.