The PSNI has said no single killer drug was responsible for the deaths of eight people in Belfast and Coleraine over the last four weeks.
Three people have been arrested by police as part of the continuing investigation, and released pending further inquiries, but officers are not linking the arrests or the deaths.
Forensics tests on the remains of the eight people, aged mainly in their 20s and 30s, are still to be completed, but the officer leading the investigation said the fatalities were not being treated as murder.
Det Chief Supt Roy McComb said there was no common factor associating the people who died and no single cause: “There is no consistent individual drug that we are finding linking any of these deaths, no single bad pill out there killing people,” he said.
“There is a sense that these eight people have died because of one bad batch, I want to dispel that myth.”
Mr McComb warned people of the risks of consuming illicit drugs, which have killed almost 1,000 people in Northern Ireland over the last decade.
'Russian roulette'
"It is a form of chemical Russian roulette: you don't know what you are taking, you cannot be sure what they contain and you are putting yourself in harm's way," he said .
Although recent attention has been focused on so-called “Green Rolex” pills, Mr McComb said all colours of tablets were potentially dangerous.
There has been a dramatic drop in the number of ecstasy tablets seized by the PSNI in the last year, from 30,000 to 6,000, but the police service has issued a warning about ecstasy bulked out with a slower-acting chemical, which carries an added risk because users may take extra pills under the misapprehension that the drug is not working.
Mr McComb said, while the most common substance seized by police was cannabis, the misuse of prescribed drugs like anti-depressants and Diazepam now killed three times more people than controlled drugs such as heroin or ecstasy.
He also called for new laws to address the problem of so-called "legal highs", substances which may be sold as plant food, bath crystals or pond cleaner, but which produce similar effects to controlled drugs.
'Fast buck'
"We need legislation to deal with the issue," said Mr McComb. "There are many people out for a fast buck. People are selling products and they don't know if that person is going to be alive the next day."
Mr McComb warned that differences in the law between the Republic, where “head shops” which sold the substances were banned, and Northern Ireland, where there was no comparable law, meant crime gangs had the option of simply moving their commodities to the North.