Six people were admitted to hospital in Cumbria last week after it was believed they had used the legal high drug Ivory Wave.
Many of those taken to West Cumberland Hospital in Whitehaven were suffering with extreme agitation and visual and auditory hallucinations, said North Cumbria University Hospitals NHS Trust.
In the most serious cases, patients were admitted to the critical care unit and placed under cardiac monitoring for up to 12 hours.
In one case it took four porters to restrain a young woman believed to have taken the party drug, the trust said.
A 17-year-old boy was also arrested on suspicion of actual bodily harm after he allegedly assaulted a man who worked at the hospital.
Another five people thought to have taken Ivory Wave were brought into the same hospital at the weekend but were later allowed home.
Last Wednesday, police seized "numerous" substances including Ivory Wave when they raided four addresses in Whitehaven and Workington.
Two Whitehaven men, aged 55 and 29, were arrested on suspicion of supplying class B drugs and then bailed as tests were carried out on the substances.
Speaking last week, Dr Kate Wilmer, consultant cardiologist at West Cumberland Hospital, warned the symptoms witnessed were "much worse" than the effects of the banned drug mephedrone.
She said: "People are coming into the hospital in an extremely agitated state with acute paranoid psychosis. If you try to give them anything to help them, they are convinced you are trying to harm them so we have had to completely knock out two or three of them in order to treat them
"All have had a very fast heart rate so we have been monitoring them in the critical care unit for about 12 hours. The drugs are getting out of their system but it is taking two to three days for the agitation and psychosis to wear off.
"I have never seen anything like it, it is really awful. The effects are much worse than with the 'plant food'."
She added the initial symptoms shown could be the "tip of the iceberg".
"What we don't know is whether this could cause long-term psychiatric problems for these people," she said.
No similar cases had been reported at West Cumberland Hospital before last week and none have so far been seen at Cumberland Infirmary in Carlisle.
A trust spokeswoman said: "We had another five cases at the weekend but we were better prepared at how to deal with them and all of them were later released to undergo home-based care."
Police issued their own warning following the arrests by drug squad officers last week.
Detective Inspector Jason Robinson, of West Cumbria CID, said: "What these incidents show us is that young people in west Cumbria are continuing to put their future and their lives at risk by taking drugs.
"We know that many so-called 'legal highs' often contain class B controlled drugs (such as mephedrone and BZP) and the risks and consequences of getting involved with them are serious.
"People wrongly assume that a substance is safe because it is currently legal, which couldn't be further from the truth. The fact is that people who take substances like Ivory Wave are taking serious risks - no-one knows what the drug is mixed with or the long-term effects that it can have.
"The only safe option is to avoid drugs and legal highs altogether.
"In west Cumbria, police are committed to reducing the impact of all drugs on our communities so we will enforce the law wherever we suspect illegal drugs are being used or sold. If we seize a legal high we will analyse it and if it is found to be unlawful then that could carry up to a five-year sentence for possession.
"If you are buying large quantities and selling it on to friends, then that's possession with intent to supply which carries a prison sentence of up to 14 years."
NHS Cumbria's director of public health, Professor John Ashton, said: "As with all so-called legal highs we need to be careful that we don't concentrate too highly on one specific substance. Instead, we need to get the message across to people that taking drugs of any kind, whether illegal or so-called legal, is a risk.
"There is no regulation for either illegal drugs or legal highs so people do not know what they are taking, what chemicals they contain and/or what effects could be. The ingredients and strength of each substance can also change from batch to batch as drugs are cut differently.
"We need to educate people of these dangers so they can make the right choices. One of the most important messages we must get across is that it's vital that if anyone does take a legal high or illegal drug is that they should not mix it with any drug or substance, particularly alcohol, as the consequences cannot be predicted.
"However, if someone does decide to take drugs, I'd ask them to please let someone else know what they are doing and what they are taking. This will mean that if anyone does start to experience negative effects then they can be helped to seek urgent medical help and be given the correct treatment."