By Catherine Marston
UK specialist correspondent, BBC News
At 29 stone (184kg) John Kelly from Stalybridge was told he would not live to see his 55th birthday.
He had a body mass index of 51. Any figure over 40 is considered to be very obese.
He suffered from breathlessness constantly and says he struggled to do even the simplest of tasks.
Looking through his wedding photos he recalls how he had to have his wedding suit made especially for him, as he could find no suit big enough to fit him.
John had been large all his life and admits he had come to accept his size as a way of life.
But then his doctor told him his life was at risk and he needed to act quickly.
John has two young sons and he says he realised he would not live to see them grow up, let alone see his grandchildren.
John was prescribed orlistat: one of the drugs which, according to latest figures, is being increasingly prescribed on the NHS.
Orlistat works by blocking the digestion of fat. It prevents about 30% of fat ingested from being absorbed.
The drug worked for a while and John says he was pleased to see the weight disappearing.
He admits some of the effects of the drug were quite difficult to adjust to and he did not find them easy to take.
Once his weight dropped and he no longer was eligible to receive the drug, he quickly found he was putting weight back on.
His doctor then tried another popular obesity drug, sibrutamine. This drug suppresses the appetite.
It works by increasing the serotonin levels of a chemical in the body called serotinin, which tells the brain the stomach is full and so patients want to eat less.
John also found this drug effective for a while.
But it had no long term effects.
"I probably lost a couple of stone each time," he explains, "and I thought yeah, brilliant, I was doing well and then they just seemed to stop, nothing happened.
"I put the weight back on and then had to approach the GP again to see if I could do something else about it".
John ended up having a far more radical intervention.
He had a gastric bypass and has subsequently lost over 12 stone (76kg).
Surgery was the only option left to him.
At the New Farnley surgery in Leeds, doctors are seeing increasing numbers of patients who need obesity drugs.
Dr Nina Amedzo says that the drugs are not given out immediately.
Patients are first advised about health, diet and nutrition.
They offer clinics designed to specifically help those needing to lose weight.
But if that advice is not followed the tablets can be a suitable option.
She warns though, they cannot be taken as some sort of wonder pill.
"In some people taking the tablets is going to be effective," she says, "but you need to emphasise it needs to be done in conjunction with dieting and lifestyle changes."
In Pontefract Diana Sutton has struggled with her weight for many years.
She has tried every type of diet club and regime she can think of.
Nothing has so far helped her maintain her weight loss.
With a BMI over 30 her doctor told her she was eligible to try obesity drugs.
She was prescribed orlistat.
Diana lost about 22lbs (10kg) and was thrilled.
She says it gave her new confidence and made her feel good.
Once her BMI dropped below 30, after six months, her GP stopped prescribing the drug.
But Diana's weight then piled back on, and she's now heavier than she was before taking the drug.
"It was never going to be a quick fix," she admits.
"You've got to readjust your whole lifestyle if you are going to lose weight and maintain that weight loss.
"So the advice you really need is you really don't need pills. You need to start now, today and change your lifestyle."
Diana believes advice on diet and lifestyle while taking the drugs could well have helped her cope once she stopped taking the tablets.
But she feels she was not offered that support.
Diet pills alone are certainly not going to provide a miracle cure to Britain's obesity problem.
They can assist some patients but there is still no substitute for a balanced diet and plenty of exercise.