Marijuana 'helps tumours grow'

Marijuana smokers may be more at risk of contracting lung cancer than tobacco smokers

Marijuana smokers may have a higher risk of contracting lung cancer than tobacco smokers, according to researchers.

A study carried out in the US found that one of the key ingredients of marijuana may promote the growth of cancerous tumours.

The researchers suggest that tetrahydrocannabinol (THC), which is the major psychoactive component of marijuana, may reduce the body's ability to fight tumours.

Previous research has found that THC can lower an individual's resistance to both bacterial and viral infections.

Increased risk

They suggested that the affect on the anti-tumour immune system, combined with the fact that marijuana smokers inhale large amounts of tar and other cancer-causing agents, could leave them at increased risk of lung cancer.

Regular use of marijuana may increase the risk of respiratory tract cancer

Dr Steven Dubinett, UCLA

Marijuana smoke deposits four times as much tar in lungs as tobacco. The tar also contains higher doses of carcinogenic hydrocarbons, which can cause cancer.

Researchers from the Jonsson Cancer Center at UCLA examined the effects of THC on the immune response to cancer in mice.

They found that mice which had been injected with THC had a reduced capability of fighting the growth of tumours.

Dr Steven Dubinett, head of the research team, said the results suggested an increased risk of lung cancer among regular marijuana users.

"What we already know about marijuana smoke, coupled with our new finding that THC may encourage tumour growth, suggests that regular use of marijuana may increase the risk of respiratory tract cancer."

The findings are published in the latest issue of the Journal of Immunology.