DETECTIVES are investigating the sudden death of eight people in recent weeks.
Now officers have warned the public to be cautious if they are offered green tablets.
Seven people in the greater Belfast area and one person in the north west have died unexpectedly.
All the victims were in their 20s and 30s.
Police have advised members of the public not to take controlled drugs, medication that has not been prescribed or to mix drugs with alcohol.
The PSNI said: “The consequences of ignoring this advice are very dangerous and potentially life-threatening.”
They specifically mentioned green tablets with a crown or castle logo.
The police said they cannot confirm that all of the deaths are drugs related, and are awaiting toxicology results.
Following the deaths, the Public Health Agency invoked its early warning system to raise awareness of the risks of drugs misuse.
Owen O’Neill from the agency said: “You can never be sure exactly what’s in non-prescribed drugs. They could be cut with other cheaper drugs such as tranquilisers or even toxic substances.
“Therefore, taking any substance that hasn’t been prescribed for you potentially puts you at risk.
“In addition, combining these substances with alcohol, or other drugs, further increases the risks and the advice from the PHA is to never mix alcohol and other drugs.
“The same advice also applies to taking alcohol with prescribed medication,” he added.
The PHA also warned of the dangers of legal highs, which are unregulated and can be perceived as being low-risk.