Two teenagers from Tiverton are in hospital after taking what are believed to be ecstasy pills.
The 14 and 15-year-olds are currently being treated. Two 16-year-olds have also fallen ill.
Officers carried out a warrant after receiving reports of the blue transformer tablets being sold to young people in the area. They found a number of the tablets, along with a small quantity of cannabis.
Police are now urging the public to be aware of the dangers of the drugs.
A 28-year-old man from Tiverton was arrested on suspicion of possession with intent to supply a Class A drug. He has since been released under investigation.
Anyone with information that may assist the police with their enquiries is asked to email firstname.lastname@example.org or phone 101, quoting crime reference CR/096555/18.
Crimestoppers can also be contacted anonymously on 0800 555 111.
Information on drugs and drug abuse can be found on Talk To Frank.