One cannabis joint as bad as five cigarettes

LONDON (Reuters) - Smoking a single cannabis joint is as harmful to lungs as having up to five cigarettes in succession, according to research published on Tuesday.

Researchers found that those who smoking cannabis damaged both the lungs' small fine airways, used for transporting oxygen, and the large airways, which blocked the airflow.

It meant that cannabis smokers complained of wheezing, coughing, and chest tightness, the study by experts at the Medical Research Institute of New Zealand found.

The researchers tested 339 people -- those who only smoked cannabis, those who smoked tobacco, those who smoked both and non-smokers.

While the study found that only those who smoked tobacco suffered from the crippling lung disease emphysema, cannabis use still stopped the lungs working properly.

"The extent of this damage was directly related to the number of joints smoked, with higher consumption linked to greater incapacity," said the authors of the report published in the medical journal Thorax.

"The effect on the lungs of each joint was equivalent to smoking between 2.5 and five cigarettes in one go."

The findings come less than a week after researchers said using marijuana increased the risk of developing a psychotic illness such as schizophrenia.

The government is currently considering whether cannabis should be reclassified as a more serious drug because of the dangers associated with stronger strains.