A 13-year-old boy is recovering in hospital after taking a legal high called Annihilator.
The teenager was rushed by paramedics to casualty when he suffered a fit after taking the over-the-counter alternative drug in Whitley Bay, North Tyneside.
A second teenager, aged 15, from Washington, Tyne and Wear, was treated by medics when she began to feel unwell after taking a similar drug.
She is recovering at home.
Northumbria Police are warning people not to take the drug, which is being sold in North East shops.
A legal high of the same name being sold online boasts of the product's "explosive strength" and warns it is "defiantly not for people new to herbal incense".
Chief Inspector Kevin Waring of Sunderland Area Command said: "We are working closely with Trading Standards to identify and visit premises selling these substances and will take any action necessary to ensure the safety of the public.
"In both these cases the substance taken appears to have been called Annihilation, Annihilator or some variation on that name. It may be being sold as a herbal incense and must not be consumed."
Officers are carrying out enquiries to establish where the substances came from.
Detective Chief Inspector Ged Noble, said: "We want people to be aware of the dangers of taking drugs, including so called legal highs and medication not prescribed for them.
"I would like to stress that the use of legal high drugs is not safe and can kill or have a devastating impact on people's health.
"These substances often contain potentially dangerous chemicals and can cause death.
"Likewise, any concoction of medication is potentially extremely dangerous and it's equally dangerous for people to take medication which has not been prescribed to them.
"Anyone who misuses drugs, prescribed or non-prescribed, is putting their life at risk and people should also be aware that this risk is significantly increased if mixed with alcohol."
Anyone who needs advice on drugs should contact FRANK on 08700 77 6600 or visit http://www.talktofrank.com
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