Here's the real study results. They looked at "macroscopic emphysema". The emphysema was detected in 1 out of 75 of the cannabis only smokers, 15 of 92 people who smoke cannabis plus tobacco, 17 of 91 tobacco only smokers, and no emphysema for non smokers. So cannabis alone only resulted in one case of emphysema, but tobacco resulted in many cases of emphysema. I don't know how they decided that one cannabis joint impairs the lungs more than tobacco because I can't read the whole study, but it sounds like something that they measured acutely, and not chronically, as cannabis didn't really cause emphysema. Never believe the news, always read the study or the study abstract. This is just like the studies that link psychosis with cannabis use, they say that someone who went a little crazy smoked literally one joint when they were a teenager, so that means that the cannabis had something to do with it. While they were smoking lots of tobacco, which people with mental illness smoke more than other people. But the studies say oh no, the tobacco is smokked because it helps to calm them. Well as it just so happens cannabidiol, the second main cannabinoid is cannabis, is a powerful antipsychotic, so they were more likely mentally ill before they smoked cannabis, and cannabis helped them.

THE EFFECTS OF CANNABIS ON PULMONARY STRUCTURE, FUNCTION AND SYMPTOMS.
Aldington S, Williams M, Nowitz M, Weatherall M, Pritchard A, McNaughton A, Robinson G, Beasley R.

Medical Research Institute of New Zealand, New Zealand.

BACKGROUND: Cannabis is the most widely used illegal drug worldwide. Long term use of cannabis is known to cause chronic bronchitis and airflow obstruction, however the frequency of macroscopic emphysema, the dose-response relationship and the dose equivalence of cannabis with tobacco has not been determined. METHODS: A convenience sample of adults from the Greater Wellington Region was recruited into four smoking groups; cannabis only, tobacco only, combined cannabis and tobacco and non-smokers of either substance. Their respiratory status was assessed using high resolution CT scanning, pulmonary function tests and a respiratory and smoking questionnaire. Associations between respiratory status and cannabis use were examined by analysis of covariance and logistic regression. RESULTS: A total of 339 subjects were recruited into the four groups. A dose-response relationship was found between cannabis smoking and reduced FEV1/FVC and sGaw, and increased TLC. For measures of airflow obstruction, one cannabis joint had a similar effect to between 2.5 and 6 tobacco cigarettes. Cannabis smoking was associated with decreased lung density on HRCT scans. Macroscopic emphysema was detected in 1/75 (1.3%), 15/92 (16.3%), 17/91 (18.9%) and 0/81 subjects in the cannabis only, combined cannabis and tobacco, tobacco alone and non-smoking groups respectively. CONCLUSIONS: Smoking cannabis was associated with a dose-related impairment of large airways function resulting in airflow obstruction and hyperinflation. In contrast, cannabis smoking was seldom associated with macroscopic emphysema. The 1:2.5 to 6 dose equivalence between cannabis joints and tobacco cigarettes for adverse effects on lung function is of major public health significance.

PMID: 17666437 [PubMed - as supplied by publisher]