Detectives are investigating whether drugs were the cause of five sudden deaths in Belfast since Friday, four on one day.
Four men and a 16-year-old girl died in the separate incidents.
The teenager and three men died on Monday and the other man died in the city on Friday.
Police are not linking any of the five incidents at this stage and said there was no one common drug suspected.
They said a combination of prescribed medication, illicit drugs and alcohol were involved.
Police Service of Northern Ireland Chief Superintendent Tim Mairs said: "Investigations are at an early stage but I would like to take the opportunity to reintroduce the dangers posed by taking any illegal drugs or any medication that is not prescribed for you.
"Drugs misuse can affect anyone and we recognise that many vulnerable people are being exploited for the financial gain of those higher up the supply chain."
In a four-week operation earlier this year, police in Northern Ireland seized £793,000 worth of illegal drugs and made 92 arrests.
From January to November last year there were 78 deaths in the region, a 28% increase on 2015.
Mr Mairs added: "Behind each of these statistics is a person and also a family who are living daily with this loss. The dangers of drug taking are clear to see."