North Wales Police believe a 19-year-old man who died on Saturday had taken "a quantity of tablets", which they believe he had been sold "by an individual within the local area."
The death of Thomas Jones from Llangefni is currently being treated as "unexplained."
Police are investigating whether his death is linked to what they believe is a form of ecstasy called "Green Apples."
DCI Andrew Williams he is "absolutely desperate to ensure that nobody else loses their life as a result of taking these tablets."
Anyone with information about people who use or supply "Green Apples" or any other controlled drug is asked to contact North Wales Police on 101, or Crimestoppers on 0800 555 111.
More top news
Swansea relieved the pressure on under-fire manager Bob Bradley with an emphatic 3-0 home victory over fellow strugglers Sunderland.
Sol Bamba was sent off after losing his cool but Cardiff hung on to claim a deserved 1-1 draw at Ipswich.
Today's rain will soon clear south-eastwards to leave a largely dry night with some long clear spells.