Police have issued a warning about a potentially fatal drug dubbed "pink ecstasy" after samples were seized in Bangor, Gwynedd.
The pills are said to look like pink ecstasy tablets but contain the potentially fatal amphetamine paramethoxyamphetamine or PMA.
Detectives said drug users may be encouraged to take more than usual because the pills act more slowly.
North Wales Police said a man from Merseyside was arrested on Friday.
The seizure of the drugs on Friday evening in Bangor, Gwynedd, was prompted by investigations by Merseyside Police.
The warning put out by detectives said the suspect drugs usually have the letter "M" on them, although the initial may vary.
The drug is also known as "Dr Death" or "Pink McDonald's".
Anyone who is offered one of the tablets is urged not to take it and to call North Wales Police.
North Wales Police Insp Dewi Jones said: "We are concerned that the drug may be being distributed in the Gwynedd area.
"We are working with hospitals, ambulance staff and pubs and clubs to highlight the dangers."
The force said a man in his 20s has been released on bail pending inquiries.
Meanwhile, Merseyside Police's assistant chief constable Andy Cooke, said: "We have strong information to suggest that tablets known a 'pink ecstasy' are being supplied by criminals here on Merseyside and ending up in the hands of young people in different parts of the country.
"Our investigation is focused on finding who is involved in the illegal supply of these drugs and taking both them, and the drugs they are peddling, out of circulation."
BBC News Wales
02 June 2012
'Pink ecstasy' drugs warning issued in north Wales