One joint equivalent to the risk of smoking 20 cigarettes
Previous studies have equated one joint to five cigarettes with regards to lung damage. However, a new study equates one joint to the damage risk of smoking 20 cigarettes. The study, published in the European Respiratory Journal, stated that those who had smoked on average one joint a day over ten years were 5.7 times more likely to develop lung cancer than those who do not smoke.
According to Dr. Richard Beasley, M.B. Ch.B., of the Medical Research Institute of New Zealand, marijuana smoke has twice as many carcinogenic polyaromatic hydrocarbons than tobacco. Additionally, marijuana users inhale differently, much deeper, and do not use filters, a bad combination. Due to the prevalence of cannabis use, it is a good idea for physicians to ask suspect patients if they are smoking marijuana. The following is an excerpt of an article from Medpage Today that goes into greater detail about the study:
Lung cancer patients were identified from hospital databases or the national cancer registers from 2001 through 2005. Most had non-small-cell lung cancer (80%) and none had lung metastasis from a distant primary.
The proportion of controls who had ever smoked cannabis was 36% after adjustment for the general population age distribution.
Overall, 26.6% of lung cancer patients in the study reported smoking at least 20 joints in their lifetime, whereas 12% of control participants had.
For every one joint-year — the equivalent of one joint per day for one year — smoked, the risk of lung cancer rose 8% (relative risk 1.08, 95% confidence interval 1.02 to 1.15).
The association between cannabis and lung cancer was strengthened with adjustment for the growth rate of lung cancer, by excluding exposure in the five years before baseline or diagnosis (RR 1.10, 95% CI 1.02 to 1.18), “as would be expected if a causal association existed.”
The association was similar to the 7% risk seen for each pack-year of tobacco smoking (RR 1.07, 95% CI 1.05 to 1.09).