One Joint of Marijuana Equals Five Cigarettes

Researchers from the Medical Research Institute of New Zealand examined 340 adults between the ages of 18 to 70 in order to assess the effects of cannabis on the respiratory system.

They found the effect on the lungs of each joint was equivalent to smoking between 2.5 and five cigarettes in one go. Professor Richard Beasley and his colleagues divided the participants into four smoking categories:

- Cannabis only

- Tobacco only

- Combined Cannabis and Tobacco

- Non smokers

All of the participants underwent high definition CT scans and took special breathing tests in order to assess how well their lungs worked.

The study, published in the medical journal, Thorax, found cannabis smoking was associated with airflow restriction and hyperinflation of the lungs. The degree of damage was related to the amount of cannabis used.

Emphysema, a progressive and crippling lung disease, was found only in those who smoked tobacco, either alone or in a combination. However, cannabis damaged the lungs by reducing the number of small fine airways; these play an important role in transporting oxygen and waste products to and from the blood.

Wheezing, chest tightness, coughs and increased production of sputum (phlegm) were all associated with cannabis use. Commenting on the finding that one joint of cannabis was similar to 2.5 to 5 tobacco cigarettes in terms of lung damage, the authors say this is because of the way a cannabis joint is smoked. "Cannabis is usually smoked without a filter, and to a shorter butt length and the smoke is at a higher temperature." Other factors associated with the study included that cannabis smokers inhale more deeply and hold their breath for longer.

"The 1:2.5 to five dose equivalent between cannabis joints and tobacco cigarettes for adverse effects on lung function is of major public health significance," they added. Meanwhile, a comprehensive analysis of the relationship between cannabis use and the development of psychosis in later life has been published in the Lancet. It concludes that the risk of psychosis increased by some 40 per cent in people who have used cannabis, with the risk rising the more the drug is used.

Cannabis is used by an estimated 160 million people worldwide. Source: Institute of New Zealand.