Regular cannabis smoking was blamed yesterday by doctors for causing a rise in a debilitating disease known as "vanishing lung syndrome".
Doctors treating respiratory illnesses in people aged 25 to 40 are increasingly finding the condition, associated with tobacco smoking, in patients who have seldom, if ever, smoked normal cigarettes.
Cannabis smokers are particularly at risk because they hold smoke in their lungs for longer than other smokers and marijuana spliffs are rolled without filters. Last month, a doctor in Newcastle had to do a lung transplant on a patient who had only ever smoked cannabis.
At the Glasgow Royal Infirmary, Dr Mark Johnson, a specialist registrar in respiratory medicine, said he had found a regular stream of patients showing signs of the syndrome, a form of emphysema that reduces the surface of the lungs and replaces it with huge cysts known as giant bullae.
The result was that the alveoli, the air sacs in the lung that permit the transfer of oxygen into the blood, are restricted by the cysts and in effect collapse the lung.
"Much more work needs to be done in this field," said Dr Johnson yesterday. "Every couple of months I finding a new patient showing signs of this condition but nobody knows for sure just how many people are affected." Research by Dr Johnson and his colleagues found patients who smoked two to three spliffs a day suffered similar lung damage to smokers who inhaled more than 20 cigarettes a day. The study found cannabis smokers inhaled more deeply and held the smoke in their lungs up to four times longer than tobacco users.
"When this smoking practice is combined with the lack of filter tips on marijuana cigarettes, it leads to a fourfold greater delivery of tar and a five times greater increase in carboxyhemoglobin per cigarette smoked," they concluded.
"It is a condition that has also been reported in heroin smokers," Dr Johnson said. He found sufferers are predominately male, between 25 and 40, and chronic cannabis smokers.
Other ill-effects associated with marijuana use included cancer, schizophrenia and impotence.
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