Metonitazene is a potent synthetic opioid
Opioids are central nervous system depressants that produce effects including pain relief, sedation and respiratory depression (where breathing slows or stops). Respiratory depression often appears more quickly with potent synthetic opioids (PSOs), increasing the risk of life-threatening overdose.
Metonitazene is a PSO. Its potency is similar to fentanyl, estimated to be between 30 and 200 times that of morphine. This means very small amounts can produce life-threatening toxic effects such as loss of consciousness, respiratory depression and hypoxia (insufficient oxygen for normal functioning).
Be cautious about any powder with a white-brown colour or tinge, especially if sold as ketamine or heroin
Two people in Melbourne were recently exposed to metonitazene after using a powder sold as ketamine. The substance was described as ‘white-brown and chunky’, but easily crumbled into a powder. Blood testing also showed evidence of heroin and it is possible that this substance could be sold as heroin.
People who are expecting to use ketamine may not know how to recognise and respond to opioid overdose. Someone might appear to be entering a ‘K-Hole’ (a dissociative state brought on by higher doses of ketamine) but could actually be showing signs of opioid overdose. Signs of opioid overdose to look out for include: breathing slowly, reduced consciousness (meaning someone is hard to rouse or wake), and tiny pupils in some cases. More information about opioid overdose symptoms can be found on the Penington Institute .
Using metonitazene or other opioids with depressants such as alcohol, GHB or benzodiazepines (‘Xanax’, ‘Valium’, ‘Mylan’, etc) increases the risk of overdose.
Reduce the risk of harm and get naloxone to reverse opioid overdose
If you experience adverse drug effects, or are present when someone has an unexpected reaction, seek help immediately by calling Triple Zero (000).
All alcohol and other drug use comes with risks, so take these precautions:
- Get free naloxone and carry it with you – no matter what drugs you think you’re getting. Naloxone is an easy-to-use medication that can reverse opioid overdose – it is safe to use even if you are not sure whether someone has taken opioids. Naloxone can be accessed free of charge at participating pharmacies and health services – find an approved naloxone provider.
- Avoid using drugs alone and ask one person to wait until the effects are known – especially if using a new batch. This will ensure at least one person can call 000 and use naloxone if required.
- Be aware that other false or contaminated drug products may circulate in Victoria, even if no specific warning has been issued about them.
- Remember, even ‘pure’ drugs can produce serious side effects and death and can interact dangerously with medications/pharmaceutical drugs. Get the facts from the Alcohol and Drug Foundation .
Contact Harm Reduction Victoria’s DanceWize and peer team for anonymous support and education from peers. Talk to them by email at info@dancewize.org.au or admin@hrvic.org.au.
If you or someone you know needs help with alcohol or drug use, call DirectLine on 1800 888 236 or visit for information and support to access treatment.
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Reviewed 03 May 2025