No single killer drug was responsible for the deaths of eight people in Northern Ireland over the last four weeks, police have said.
As investigations continue, the PSNI revealed that three people have been arrested and questioned over the deaths.
They were detained in Belfast and the north west over a four-week period recently and have been released pending further inquiries but investigators are not making any connection between the deaths or between the arrests.
Detective Chief Superintendent Roy McComb said: "There is no consistent individual drug that we are finding linking any of these deaths, no single bad pill out there killing people."
People aged mainly in their 20s and 30s died and the PSNI is still awaiting the results of forensics tests.
Separately, the force has issued an alert about ecstasy tablets laced with a bulking chemical which can prove even more deadly because it could encourage abusers to take extra pills in the mistaken belief that they are weak.
A recent batch seized contained "Green Rolexes" - which can sell for a couple of pounds each - but the detective said all colours of tablets were potentially dangerous.
The senior officer added that mixing drugs with alcohol was like "Russian roulette" and issued a stark warning about some prescription drugs like anti-depressants or tranquillisers which he said kill three times more people than heroin or ecstasy - often in their late 30s.
"If you are mixing drink with any type of unprescribed medication you are buying over the internet that is a game of chance and the odds are not in your favour," he added.
He said around 150 organised crime gangs were supplying drugs, which killed 110 people last year and almost 1,000 in a decade.
He warned that dealers in so-called legal highs were exploiting differences in the law between the Republic of Ireland and Northern Ireland and unhindered travel between jurisdictions to peddle their potentially lethal wares.