Two people have died from heroin overdoses after taking drugs they thought were cocaine, as health authorities urge caution when using illicit substances.
NSW Health officials said four people had recently suffered heroin overdoses after believing they had used cocaine, with two of them dying.
The other two required hospitalisation.
NSW Health chief addiction medicine specialist Hester Wilson said consuming a single line of heroin could cause an overdose.
"It is important that people recognise the signs of an opioid overdose early and know how to respond," she said.
"Opioids such as heroin can cause pin-point pupils, drowsiness, loss of consciousness, slowed breathing or snoring and skin turning blue or grey and can be life-threatening."
A similar warning was issued in the ACT on August 30, after four people died of suspected drug overdoses in a two-month period.
Police suspected either high drug purity levels or the presence of synthetic opioids including fentanyl were behind the deaths.
Dr Wilson said people who planned to use drugs such as cocaine, MDMA and opioids should carry naloxone with them.
Naloxone, which does not require a prescription, reverses the effects of opioids.
"One of the dangers of illicit drug supply is the strength and contents of the substance you are getting is unknown and can be inconsistent," Dr Wilson said.
"Heroin and other opioids can be sold as or found in cocaine, methamphetamine, and MDMA, you cannot always tell the difference between these drugs by appearance."
