Four people arrested on suspicion of supplying drugs following the death of a 19 year old man have been released on police bail and a fifth person has been detained.
States of Jersey Police say quantities of drugs and cash have been seized.
A fifth person, a 20 year old man, has been arrested and is currently in police custody. A warrant was executed in St Helier just before midnight on Saturday. More drugs and cash have been seized.
Detectives are probing the circumstances surrounding the death of a 19 year old man in St Lawrence in the early hours of Saturday morning. It is suspected he had taken MDMA.
Family Liaison officers are supporting the family.
Paramedics were called to an address just before 2.30am. Three other people were also treated in hospital for the effects of the drug. They were later discharged and police said they were 'fit and well'.
The force has described it as a 'dynamic and fast-moving investigation' and say they 'continue to work hard to secure evidence and to ensure the ongoing safety of our island community.'
Islanders have been warned against taking MDMA, and anyone who has and who is feeling unwell should seek immediate medical attention.
There have been no further MDMA -related hospital admissions.
Anyone with information that could help the investigation should call 612612 or Crimestoppers on 0800 555 111.