A study by New Zealand's Medical Research Institute identified the dose equivalence between cannabis and cigarette smoking and found that longtime pot smokers can develop symptoms of asthma and bronchitis along with obstruction of the large airways and excessive lung inflation, according to the paper released ahead of print in the journal Thorax.
"The study shows that one cannabis joint causes a similar degree of lung damage as between 2.5 and five tobacco cigarettes," said lead author Sarah Aldington.
However, the study found that the progressive chronic lung disease emphysema, often associated with cigarette smoking, was uncommon among cannabis smokers. Only 1.3% of the long-term pot smokers were found to have signs of the disease compared to 16.3% of those who combined cannabis and tobacco and 18.9% of those who only smoked tobacco.
Cannabis smokers had symptoms that included wheezing, coughing, chest tightness and phlegm - all of which were associated with tobacco smokers except chest tightness.
The study, which used lung function tests, high-resolution X-rays and questionnaires, also revealed that among cannabis smokers damage occurred to the small, fine airways which are important for taking in oxygen and removing waste gases. The extent of damage rose in proportion to the number of joints that had been smoked.
Last week, another study published in The Lancet medical journal suggested that using cannabis may increase the likelihood of becoming psychotic, with even infrequent use potentially raising the overall small risk by up to 40%.
The three-year Thorax study involved 339 people in New Zealand, where pot smoking is fairly common. An estimated 160 million people use pot worldwide. Participants were recruited into four groups based on smoking habits - non-smokers, tobacco only smokers, tobacco and cannabis smokers and cannabis only smokers.
To qualify as a long-term cannabis user, participants had to have smoked a minimum of one joint a day for five years, said institute director Richard Beasley, who also participated in the study. Tobacco users had to have smoked a pack a day for one year.
Earlier studies have shown that smoking one joint results in three to five times more carbon monoxide and tar inhaled than smoking a cigarette of the same size. The New Zealand research also showed that the "products of combustion" in cannabis are very similar to tobacco, Beasley said.
Part of the reason for this is the way joints are smoked, with users often inhaling and holding the smoke in longer for a better hit. Cannabis joints typically do not have filters and they have shorter butts than cigarettes with a higher smoke temperature. Pot also is commonly smoked through various types of pipes.
Jeff Garrett, president of the Australia-New Zealand Thoracic Society who was not involved in the study, said that although the study found emphysema among cannabis smokers relatively rare, he emphasized that it does occur.
Hospital specialists also are seeing an increasing number of people with emphysema specifically related to cannabis smoking, he said.
Source: Associated Press, July 31, 2007 -
