John has only ever taken Spice once, but that was enough.
One sunny Sunday afternoon on Devonshire Green he was passed something to smoke.
The next thing he remembers is waking up in an ambulance.
Years later, he still has epileptic fits and must keep an assist dog to help him preempt his regular seizures.
Now, he wants to share his experiences to warn others of the dangers the former legal high can hold.
“I thought it was just another joint,” says 51-year-old John.
“It was back when it was legal and my friend had bought some from the shop on Division Street.
“He said I had a fit within seconds of inhaling it – the next thing I knew I was in an ambulance.”
When John finally came round he said he could not move – the ‘zombie state’ that is so redolent of the much-maligned substance.
“It wasn’t a high it was the lowest of the low – it was horrible,” he says.
“No matter how drunk I get I would never do it again.
“The people at the Cathedral must be doing this every day. I don’t know how they are still alive.”
“The authorities need to crack down on it - treat it as a class A drug.”
John said he has had experiences with other drugs, none of which had anything like the devastating effect that Spice had.
“Every now and then when I was first in the armed forces people would pass a joint around,” he said.
“I went through the rave scene as well and never had any problems at all.
“But what kind of high is it when you are just slumped over? And you leave yourself so vulnerable as well.”
John – who now works in Sheffield in telecommunications – was in the forces for nine years and says he has always kept himself fit and healthy.
After taking Spice, however, his health deteriorated rapidly.
His first seizure happened shortly afterwards, and he was diagnosed with epilepsy.
His seizures are now largely kept under control with medication and he lives a relatively normal life.
Nevertheless, he still needs his assist dog to help him realise when he is about to have one and take action to protect himself.
He also has to notify prospective employers about his health problems, and says some are jittery about employing someone who could be taken ill at any moment.
A neurologist who has treated John told him his condition was probably caused by the drug, although this couldn’t be medically proven.
Looking back, he says he just wishes he’d never tried it, but he still hopes to use his experience to save other people making the same mistake he did.
“I just didn’t think about the consequences of my actions,” he says.
“I would say to any kids out there – just don’t. Please don’t.”
“I can understand them wanting to try things and experiment – I did it myself.
“But I don’t regret any of that – the only thing I regret is Spice. It is poison.”