If a person smokes one cannabis joint the impact on his/her lungs is the equivalent of smoking up to five cigarettes concurrently, says a report in the journal Thorax.

The researchers examined data on 339 adults from an ongoing study of respiratory health: they were all under the age of 70. The adults were divided into four different groups:

— 75 people smoked only cannabis, at least one joint per day for five years (no cigarettes)
— 92 people who only smoked tobacco, a pack of 20 per day for one year or more (no cannabis)
— 91 people who smoked both tobacco and cannabis
— 81 people who did not smoke anything – neither cannabis nor tobacco

It was found that those who smoked both tobacco and cannabis had a tendency not to consume as much tobacco as those who smoked just tobacco.

They all had a CT (computed tomography) scan of their lungs as well as special breathing tests. They were also asked about their smoking habits.

Emphysema was only identified among those who smoked just tobacco or both tobacco and cannabis, but not among non-smokers and cannabis only smokers. Cannabis smokers did complain of phlegm, chest tightness, cough and wheezing.

The findings showed that cannabis does damage the lungs and impairs their good function. The number of small fine airways in the lungs was significantly lower among the cannabis smokers. The researchers found that the large airways were damaged as well – the airflow was blocked and the lungs had to work harder. The intensity of the damage appears to be directly linked to frequency of cannabis smoking.

The scientists estimate that the effect of one cannabis joint on the lungs is equivalent to consuming 2.5 to 5 cigarettes simultaneously (all at the same time).

The authors added that the method of smoking cannabis is strongly linked to the effect it has on the lungs. Cannabis smokers do not use a filter, they inhale deeply, and often they hold their breath at the end of an inhalation.

“Effects of cannabis on pulmonary structure, function, and symptoms”
Online First Thorax 2007; doi: 10.1136/thx.2006.077081

Written by: Christian Nordqvist