Warning over cannabis lung harm. BBCnews.Jan 31,2008. Heavy cannabis users may be at greater risk of chronic lung disease – including cancer – compared to tobacco smokers, two studies suggest. One study found a higher risk of lung cancer for those who smoked one joint a day compared with those who smoked 20 cigarettes a day over the same period. [ See ]Image from BBC Ciencia. see also: Cannabis now three times stronger.