SOMEWHERE in Alaric Thompson's head, a light switched on, and he found himself staring into unfamiliar eyes. As the picture cleared, he saw the concerned face of a paramedic gazing down at him. Slowly taking in his surroundings, he registered that he was in an ambulance and on the way to hospital. It was explained to him that he had had a fit, and that his parents had called the ambulance when it showed no signs of abating.

He would later learn that it took the combined strength of his father and a neighbour to hold him down as his limbs flailed wildly. The episode, at the beginning of the Easter holidays, was to mark the beginning of a nightmare for 29-year-old Mr Thompson, who lives just across the Pennines in the historic market town of Lancaster.

A few days earlier, he had gone to his GP and asked if there was anything he could prescribe to help him stop smoking. His partner Lynne Millington, 23, had done the same. When the doctor suggested Zyban, Mr Thompson thought it sounded ideal.

"I thought it was the answer to our dreams," he says. "In the past, whenever we had tried to give up smoking, one of us had let the other down. We had gone through everything, and nothing had worked."

The couple each took their first pill on a Thursday, and by Saturday, Mr Thompson was feeling unwell. "We were at my mum and dad's caravan, and in the early hours of the morning, I started shaking uncontrollably and having cold sweats," he says. "It was really quite worrying." When Ms Millington rang the NHS helpline, she was told the symptoms were just side-effects, and that her partner could either sit them out for 48 hours or stop taking Zyban and remain a smoker.

Unsurprisingly, Mr Thompson opted for the latter: "I could handle 48 hours if it meant a lifetime of not smoking," he says. It was after the third pill that he suffered his first fit. He was kept in hospital under observation for four days, but when he questioned doctors about why the fit had occurred, their responses were vague. "I stopped taking Zyban immediately, and a number of doctors mentioned it, but nobody would say it was the cause," says Mr Thompson.

Following his release, the fits continued, leading to more hospital stays and a series of tests. Mr Thompson was asked if he had a history of epilepsy in the family, which he has, and put on an anti-epilepsy drug. But the fits persisted, wreaking havoc with every aspect of his life.

"I started to have fits at home, in the car, and elsewhere," says Mr Thompson. "They varied from twice to ten times a day. It was awful - I didn't know what was going on. I was rushed into hospital three or four times, then eventually they gave me a 24-hour brain scan and there was no sign of epilepsy."

Mr Thompson was banned from driving for a year and when we spoke, had been absent from his teaching job for five weeks. But the worst aspect of his illness has been its effect on his partner, parents, and four-year-old daughter, Lauren. "It's affected me and our family incredibly," he says. "The past five weeks have been horrendous. Lauren has had so many babysitters, and Lynne has had her finals at university. She had to get a letter from the doctor to explain that she might not do as well because she's had so much to deal with."

For more than a fortnight now, Mr Thompson has not had a fit. The high-strength epilepsy drugs he is taking seem to work, but doctors cannot confirm that he suffers from the condition. As he is unwilling to risk another fit - and another year's driving ban, he is resigned to taking medication for the rest of his life. But he has been left with a pervading sense of bitterness and injustice.

"I can't prove it, but in my own mind, I'm convinced that Zyban has caused my illness," he says. "I think the drug should be taken off the market immediately, and a hell of a lot more research should be done on it."

Despite the reported problems with the drug, including the death of 21-year-old air hostess Kerry Watson, who took it alongside anti-malarial medication, it continues to be prescribed in Britain, including the North-East.

An estimated 360,000 smokers were taking it up to the end of February, of whom 5,352 reported adverse reactions.

Recently the Department of Health's chief medical officer issued a reminder to GPs to exercise caution when prescribing Zyban. It advises against its use by those "with a current or previous seizure disorder", or "predisposing factors for seizure", and states that the Committee on Safety in Medicines is "continuing to monitor closely the safety of Zyban."

Dr John Canning, a member of the British Medical Association's GP Committee, and secretary of the Cleveland Medical Committee, does not interpret the advice to include those with epilepsy in the family. "The relationship between family history and getting epilepsy is not very strong," he says. He takes the view that all drugs pose risks, and does not consider Zyban any more dangerous than other medication. But he believes it is important that patients are aware of the possible side effects. "One of the first things I would mention to someone is that there is a chance of fits," he says. Dr Canning would not prescribe Zyban to those who drive for a living.

Its manufacturer, GlaxoSmithKline, denies that the drug is dangerous. It claims that adverse reactions are not necessarily caused by Zyban alone. For every horror story such as Mr Thompson's, there appears to be a glowing testimony to the merits of Zyban.