Several people have been hospitalised after taking yellow ecstasy pills with a UPS logo on them.
Police said the tablets, which contain a high level of MDMA, were found to be in circulation in clubs in Worthing, West Sussex.
The Public health Agency (PHA) has issued a warning and police in Northern Ireland confiscated more than 1,200 similar looking tablets last week.
The main risks from using MDMA are heatstroke, water intoxication caused by drinking too much fluid, and heart failure.
Sussex Police Sergeant Mandy Symes said: "While we obviously do not condone the criminal use of this drug, this clearly presents an increased risk to those who purchase and use this drug.
"There have so far been no reports locally or, as far as we are aware, elsewhere in Sussex, of anyone seeking medical help as a result - but we take this issue very seriously and we want to see these drugs removed from circulation.
"The purpose of this message is to both raise awareness amongst current users and to ensure that partner agencies involved in the treatment and engagement with those who are addicted can brief their staff and clients and raise awareness."
Anyone with information should call Sussex Police on 101, email email@example.com or call Crimestoppers on 0800 555111.