The sudden death of a 16-year-old girl in Belfast is one of four fatalities on Monday being investigated to establish if drug misuse was a factor, police have said.
A fifth death on Friday is also being treated as a possible drugs incident.
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.
Three men and the teenage girl died in the separate incidents on Monday in Belfast with the other fatality on Friday. Post mortem examinations were taking place on Tuesday to determine exactly what caused each death.
Police said four of those who died were a 26-year-old man in the Riverdale Park North area of west Belfast, a 25-year-old man in the Hannahstown area of west Belfast, a 16-year-old female in the Great Victoria Street area of Belfast and a 28-year-old man in the Utility Street area of south Belfast.
It was originally reported that one of the deaths occurred in Killough but it has now been confirmed that the man concerned was from Killough but died in Belfast.
PSNI Detective Chief Superintendent Tim Mairs, said: “Investigations are at an early stage but I would like to take this opportunity to reinforce the dangers posed by taking any illegal drug or any medication which is not prescribed for you. Misuse of drugs can affect anyone and we recognise that many vulnerable people are being exploited for the financial gain of those higher up the supply chain.
“The number of deaths in Northern Ireland connected to drug use is on the increase and this is a concern.
“Sadly, these are all preventable. In fact, more people are dying from misuse of opioid drugs in Northern Ireland than in road fatalities, which is a very stark reality.”
Police said that in a four-week operation earlier this year, the PSNI seized £793,000 worth of illegal drugs and made 92 arrests. From January to November last year there were 78 deaths in the Province – 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 involved in drug taking are clear to see. They have devastating effects not only on the individuals, but also to their families and communities who have to deal with the negative behaviours drug taking induces.
“The seizure of £793,000 worth of drugs over the past four weeks is ongoing proof that our commitment to acting upon information provided by communities has paid off.
“We could not carry out the job we do without the help of communities. We continue to encourage anyone with information regarding drugs to come forward and help us reduce the threat of dangerous and illegal drugs on the streets.”
Seamus Mullen of the Public Health Agency (PHA) said: “All drugs carry risks, therefore the PHA strongly recommends that you do not take them. If you have taken drugs and are feeling unwell, please seek medical help urgently.
Mr Mullen added: “If you think you might have a problem with alcohol and/ or drugs and would like to get help please visit www.drugsandalcoholni.info for information on support services near you.”
In November 2014, a coroner in Belfast warned that, over a two year period, more than 20 people in Northern Ireland were believed to have died as a result of recreational drug abuse.