Eighteen people were arrested for drugs offences at the V Festival in Chelmsford on Friday.
Essex Police said the arrests sent a "strong message" to anyone thinking about using or supplying drugs at the festival in Hylands Park.
Four people were arrested on suspicion of possession of drugs with intent to supply. They are a 21-year-old man from Epsom in Surrey, a 20-year-old man from Chelmsford, a 24-year-old man from Chelmsford and an 18-year-old man from West Drayton in Middlesex.
A further six people were arrested on suspicion of possession of drugs and eight people were arrested on suspicion of being involved in the supply of drugs.