Effects of cannabis on pulmonary structure, function and symptoms.
BACKGROUND
Cannabis is the most widely used illegal drug worldwide. Long-term use of cannabis is known to cause chronic bronchitis and airflow obstruction, but the prevalence 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 (HRCT) 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
339 subjects were recruited into the four groups. A dose-response relationship was found between cannabis smoking and reduced forced expiratory volume in 1 s to forced vital capacity ratio and specific airways conductance, and increased total lung capacity. For measures of airflow obstruction, one cannabis joint had a similar effect to 2.5-5 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 1:2.5-5 dose equivalence between cannabis joints and tobacco cigarettes for adverse effects on lung function is of major public health significance.
Medical Research Institute of New Zealand, P O Box 10055, Wellington 6143, New Zealand.
Sarah
S
Aldington
Mathew
M
Williams
Mike
M
Nowitz
Mark
M
Weatherall
Alison
A
Pritchard
Amanda
A
McNaughton
Geoffrey
G
Robinson
Richard
R
Beasley
D000328:Adult; D000368:Aged; D005260:Female; D005541:Forced Expiratory Volume / Q000502:physiology; D006801:Humans; D008171:Lung Diseases / Q000000981:diagnostic imaging / Q000209:etiology* / Q000503:physiopathology; D008297:Male; D008385:Marijuana Smoking / Q000009:adverse effects* / Q000503:physiopathology; D008875:Middle Aged; D012135:Respiratory Sounds; D012907:Smoking / Q000009:adverse effects / Q000503:physiopathology; D014057:Tomography, X-Ray Computed; D014797:Vital Capacity / Q000502:physiology