Cluster headaches share some similarities with migraines and sufferers find them extremely debilitating.

"You go through a point when it's too sore to scream and all you can do is whimper, begging God over and over and over again," said Flash.

"I've fantasised about blowing my brains out so many times you wouldn't believe it."

Flash first experienced cluster headaches as a teenager, but the condition went undiagnosed by his GP for over three years -- until Flash decided to investigate his own condition.

"My doctor didn't have a clue," Flash revealed.

"He said I was grinding my teeth, or it was my sinuses."

"I was worried I had a brain tumour, so I got a book out about the brain."

"I looked at migraine, and cluster headache was on the next page."

"I took the book to the doc and he agreed it might be what I had."

But even after diagnosis, the GP failed to give Flash the help he needed.

"My doctor did the worst thing you can do to a person with cluster headache -- he put me on normal analgesics," he said.

"Aspirin, paracetamol, codeine -- doubling up on the codeine -- taking whatever you're allowed to each day."

"It took the lining off my stomach, and it aggravated the attacks until they got out of control."

It was Flash's decision to attend university that led him to the cure for his headaches.

He encountered LSD for the first time and whilst his experience on the drug was mixed, the ensuing months were free of cluster headaches.

The following two years were pain free, but Flash then began experiencing ''shadows' -- a term sufferers use to describe the sensation that an attack is imminent.

"There was no way I was going down without a fight," he said.

"I made a list of everything I'd done differently in 1993 and 1994 --and one thing stood out."

"It was the acid."

At this stage, Flash no longer knew any LSD dealers -- so he decided to experiment instead with psychedelic mushrooms.

"It was 50 per cent recreational and 50 per cent theoretical -- I was desperate," admits Flash.

The 'shadows' went away and Flash began taking a small dose of mushrooms every three months over a year.

"I started to tell people about it -- but they thought I was mad," he confesses.

He decided to establish whether the mushrooms really were a cure by deliberately inducing an attack by drinking whisky, followed by mushroom tea.

"The cluster attack came on full force and lasted 10 minutes, before it went 'pop' and was gone," he said.

"That was one of the best moments of my life."

"I'd kicked its arse, properly."

Anecdotal tales such as these have now inspired academic research into hallucinogens as a way to treat cluster headaches.

"It is a life-or-death situation for some of these patients," said Professor John Halpern of Harvard Medical School .

"This is a seriously debilitating condition"

"Your jaw drops at what people go through, the torture they go through just to get properly diagnosed."

"Many people do OK using conventional medication, but we have a moral obligation to those people that are treatment-resistant."

Professor Halpern and his colleagues Dr R. Andrew Sewell and Dr Harrison G. Pope have published their research in the journal Neurology.

"Psilocybin and LSD may be effective in treating cluster attacks, possibly by a mechanism that is unrelated to their hallucinogenic properties," reads the report.

But they are careful to distance themselves from illegality.

“This report,” they added, “should not be misinterpreted as an endorsement of the use of illegal substances for self-treatment of cluster headache.”

For now, Flash remains symptom-free -- and anonymous.

As co-director of a company with 100 employees, he cannot afford to be identified with illegal drugs.

"Some people think that this cure is not palatable," he says.

"But I don't think you get multiple chances with something like this."

"This is the best treatment we have."