A man has been arrested on suspicion of manslaughter following the deaths of three people in Newcastle who are thought to have taken the drug Spice.
The deaths occurred within 24 hours on Friday and Saturday and are believed to be linked to a particularly "dangerous batch", the city council said.
The three men who died were aged 23, 26 and 34.
Nine males aged 14 to 44 and two women, aged 25 and 33, were arrested in Newcastle.
One of the men, a 27-year-old, was held on suspicion of manslaughter in relation to two of the deaths.
The other 10 people were arrested on suspicion of drugs offences, although the 14-year-old boy and 25-year-old woman have since been released with no further action to be taken against them.
A 35-year-old man and a 33-year-old woman remain in custody, the remainder of the group arrested have been released while inquiries continue.
A quantity of drugs and paraphernalia was also seized.
Northumbria Police said officers remained concerned for the wellbeing of anyone who had taken or purchased the drug in recent days.
Separately, six people were taken to hospital in the Cleveland area after taking what police described as "illicit tablets".
The force there initially said 11 people needed treatment over the weekend and believed it was related to a bad batch of Spice.
It has since confirmed it is not linking the two incidents and no arrests have been made.