Four men have been hospitalised after taking legal highs days before a blanket ban comes into force.
Police in Rochdale were called to deal with the string of casualties on Tuesday and warned so-called new psychoactive substances, which are set to become illegal on Thursday, can cause serious harm.
One of the men, who is in his 30s and took a legal high called Clockwork Orange, is in a life-threatening condition in hospital after falling unconscious at a home in Milnrow Road at around 3.50pm.
Half an hour later officers were called to Oldham Road where a man in his 40s had collapsed after taking a substance called Pandora's Box. He has since discharged himself from hospital.
A third man, in his 30s, fell unconscious after taking Kronic at an address in The Butts, while a fourth, in his 40s, was also hospitalised after taking legal highs near the junction of Drake Street and Oldham Road.
Detective Inspector Lee Hopwood said: "Despite issuing warnings about the dangers of these so-called 'legal highs', these are now the latest people to have been taken ill after taking them in the past few days.
"I cannot stress enough how dangerous they are and even though they might not be illegal, please do not take the risk. They can seriously harm you and in the case of these men they are now in hospital because of it.
"Please think about the effects of these substances and do not take them. If you think someone you know might have taken 'legal highs' then please get medical attention immediately."
New psychoactive substances, commonly known as legal highs, which mimic the effects of traditional drugs like ecstasy and cannabis, are being outlawed amid concerns they have been linked to deaths and are fuelling anti-social behaviour.
The blanket ban on legal highs has been branded unscientific and its implementation has been delayed by more than a month amid concerns it is unenforceable.
Commander Simon Bray, the National Police Chiefs Council's lead on new psychoactive substances, warned at the weekend that the ban could drive dealers onto the so-called "dark web" - unlisted websites that are difficult to trace.