Smoking a single joint of cannabis has the same impact on breathing capacity as up to five cigarettes, a new study shows. The researchers say this may be because cannabis users tend to inhale more deeply and, because joints are smoked without a filter, the smoke is hotter when it hits the lungs. Researchers from the Medical Research Institute of New Zealand publish their findings online in the journal Thorax. Doctors recruited 339 volunteers who were divided into four categories: those who smoked only cannabis, those who smoked only tobacco, those who smoked both, and those who smoked neither. Cannabis-only...