Drug users are being warned that they will be arrested if they're found in possession of 'lethal highs'.
It comes after Northumbria Police made 12 arrests connected with the illegal substances in just four days.
Officers in Newcastle city centre have dealt with a spike in the number of people using the drugs known as New Psychoactive Substances (NPS).
There have been a significant number of reports of people having taken what is believed to be 'Power' or 'Spice'. A handful of those people have been taken to hospital as a precaution but nobody has fallen seriously unwell.
Police say the reports are causing a huge strain on emergency services in the city as well as being distressing for visitors.
"We're finding that many of these users still believe NPS to be legal. That is definitely not the case."
A full investigation has been launched and six people have been arrested in connection with supplying the drugs. A further six people have been arrested on attempted possession of NPS.
Superintendent Paul Knox, of Northumbria Police's Central Area Command, says people need to be aware of what they are taking:
"Despite the number of reports only a handful of people have been taken to hospital and nobody has fallen seriously unwell. However, these drugs are unpredictable and there is the potential that somebody could die.
The investigation into the use of NPS in Newcastle is being led by a dedicated set up by Northumbria Police in 2016. The force has been working closely with Newcastle city council, North East Ambulance Service and Public Health.
In the past 18 months their work has seen hundreds of thousands of pounds worth of NPS seized in a number of raids and, when the drugs were still legal, saw a number of shops that stocked the dangerous substances shut down.
Investigations into the supply of lethal highs and other illegal substances across the force area are ongoing and anyone with any information on lethal highs, or the identity of those supplying them, can get in touch with police.
"Our work to identify those flooding our streets with NPS is being ramped up a gear and people need to realise that we will not tolerate the use of NPS in Newcastle."