The force confirmed that a 16-year-old, who was hospitalised before the weekend, was still in a critical condition.
Seven arrests have been made in connection with that incident. Six of those people have been released on bail.
Then yesterday morning, a 19-year-old girl was admitted to hospital after taking a similar substance. She has since been released.
Detective Inspector Lisa Sylvester said that investigations into both serious incidents were under way.
‘At this time we believe the substance is MDMA – commonly known as Ecstasy – in the form of either crystal or rock enclosed in a capsule,’ she said.
‘Anyone who has taken a similar substance should seek medical advice urgently. Anyone who has purchased a similar substance should safely dispose of it if they have not yet ingested it.
‘If anyone is aware of friends who have taken a similar substance please check in on them to ensure that they are safe.’
Director of Public Health Dr Nicola Brink has also issued a warning about the drug.
‘The risks of using MDMA include heatstroke, water intoxication caused by drinking too much fluid, and heart failure,’ she said.
‘For some people these can be very serious and life-threatening. From a public health perspective I would therefore strongly advise people against taking MDMA.
‘Furthermore, mixing alcohol and drugs, or different types of drugs, can be dangerous. I would therefore urge everyone to consider these facts very carefully.’
A Guernsey Law Enforcement spokesman said they were not saying that other illegal drugs were safe, as there was no way of knowing if these unregulated substances are safe or how someone might react to them.
The force’s message is that people should not take any illegal drugs.
. Anyone with information about these incidents or any other drugs should call Guernsey Police on 725111, Crimestoppers, anonymously, on 0800 555 111 or the Guernsey Confidential Drugsline on 0800 318 318.