Warnings have been issued about the “flood” of legal highs sweeping prisons after two inmates from a Wetherby jail were taken to hospital suffering from side effects.
The men, who are serving sentences at HMP Wealstun, were treated by doctors after suffering a reaction to a cannabis substitute known as Spice.
The substance can cause a string of side effects including heart palpitations and acute psychosis.
The Prison Service said the two men were released the same day without suffering serious injury.
But Glyn Travis, assistant secretary of the Prison Officers Association, said the spread of legal highs in prisons was a real concern.
He said: “The system has not managed to work out how to crack down on them. It’s illegal to bring substances into prison, but the flood of illicit substances is causing us real problems.
“There has been a number of suspected serious illnesses and deaths because of it and levels of violence are on the increase.
“It’s an epidemic.”
He said legal highs were cheap and difficult to detect and the impact on the health of prisoners was proving a drain on the public purse.
West Yorkshire Police’s drugs co-ordinator Bryan Dent said substances like Spice and Black Mamba were a health risk because users never knew what they contained.
“The problem is that, because they are labelled as legal, people have the impression that they are safe. We’re trying to get the message out that this is not the case,” he said.
A Prison Service spokesman said action was being taken following the incident at Wealstun.
“We take a zero tolerance approach to drugs in prisons. Those caught with drugs face having time added to their sentence,” he said.
“We deploy a range of robust search and security measures to detect drugs in prison.”