Cannabis smoking could be responsible for a rise in the debilitating illness known as vanishing lung syndrome, doctors warned yesterday.

Treatment of such respiratory disorders in younger patients who have seldom, if ever, smoked normal cigarettes, is on the increase, according to Martin Johnson, specialist registrar in respiratory medicine.

"It is not normally a common condition, but there is a possibility that it is common in heavier cannabis smokers," he told the Glasgow Herald.

"You can develop quite a lot of lung damage before you become symptomatic. We had one whose lung was collapsing and another disabled by breathlessness."

Dr Johnson said there was a stream of patients in their 30s at Glasgow Royal Infirmary with symptoms which turn out to be vanishing lung syndrome.

The disease causes the alveoli - air sacs - in the lung that permit the transfer of oxygen into the blood to be dis placed by big cysts, called giant bullae, cutting the lung's function by up to a third and crowding the chest cavity.

Dr Johnson said the problem with vanishing lung syndrome might not be so much to do with the content of the drug as with the way it is smoked. The condition had also been reported in heroin smokers.

"We were wondering what the mechanism was and we suspect it is because when you smoke drugs you tend to take much deeper breaths and hold it in longer than you would with tobacco," he said.