Sci. & Tech.
Cannabis smoke more toxic than puffing tobacco

GUARDIAN NEWS SERVICE

By Ian Sample in London

Cannabis smokers are exposed to more toxic chemicals in each puff than those who smoke only tobacco, scientists have found. Earlier research shows cannabis smokers are more prone to lung damage than cigarette smokers.

In tests, directly-inhaled cannabis smoke contained 20 times more ammonia than cigarette smoke, five times more hydrogen cyanide and five times the concentration of nitrogen oxides, which affect circulation and the immune system.

Researchers led by David Moir at Health Canada investigated after noting there are 4,000 chemicals and toxins listed for tobacco smoke but no such list for cannabis. They set up machines that "smoke" the plants and collect the fumes.

The scientists first analysed smoke that would be inhaled directly, but later examined "sidestream smoke", which accounts for 85% of the fumes you inhale if you sit next to a smoker. This smoke contained higher levels of almost every toxin measured, except for compounds known as polycyclic aromatic hydrocarbons, which were more concentrated in directly inhaled cigarette smoke.

The chemicals combine to cause harmful health effects. Polycyclic aromatic hydrocarbons have been linked to reproductive disorders and cancer while, at high levels, ammonia can cause asthma. Hydrogen cyanide causes weakness, weight loss and gastrointestinal problems.

"Cannabis contains similar carcinogens to tobacco, in particular volatile organic compounds," Stephen Spiro of the British Lung Foundation told New Scientist magazine. "That these exist in similar or even higher proportions to tobacco smoke is a great worry."

In July scientists in New Zealand reported that smoking a single cannabis joint could cause as much lung damage as five chain-smoked cigarettes.

Chest scans showed cannabis damaged the large airways in the lungs and reduced the number of small airways that transport oxygen to and from blood vessels in the lungs.

Much of the damage is believed to be caused by the way cannabis is smoked: one study found smokers inhale cannabis one-third more deeply than tobacco and hold it in up to four times as long.

Sci. & Tech.

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