Victoria Health issues safety warning after 'life-threatening' opioid sold as ketamine

A dangerous "toxic" opioid has been mis-sold as ketamine in Melbourne.

The Department of Health issued the warning today, saying a "yellow powder containing the potent opioid 'protonitazene' has been mis-sold".

The department says small amounts of the opioid can be toxic.

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"There have been serious recent hospitalisations associated with this powder," the department on its website.

"The product appears to have strong and fast-acting effects, leading to loss of consciousness and respiratory depression which may cause life-threatening hypoxia (insufficient oxygen for normal functioning)."

Signs of overdose include tiny pupils, slow breathing and unconsciousness.