Study: 1 joint is as bad as 5 cigarettes

July 30, 2007

, Associated Press

A single joint of marijuana obstructs the flow of air as much as smoking up to five tobacco cigarettes, but long-term pot use does not increase the risk of developing emphysema, new research suggests.

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 Tuesday 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 marijuana and tobacco and 18.9% of those who only smoked tobacco.

Marijuana smokers had symptoms that included wheezing, coughing, chest tightness and phlegm — all of which were associated with tobacco smokers except chest tightness.

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