Marijuana may be greater cancer risk than tobacco, research suggests

June 21, 2000
Web posted at: 3:19 p.m. EDT (1919 GMT)

From staff reports

(CNN) -- Smoking marijuana may be a greater cancer danger than smoking tobacco, a new study from the University of California at Los Angeles suggests.

The research, conducted on mice, was published in the July issue of the Journal of Immunology. The UCLA researchers studied the effect of tetrahydrocannabinol, or THC, the major euphoriant in marijuana.

They found that THC can promote tumor growth in mice by impairing the body's anti-tumor immunity system. Mice with normal immune systems had significant tumor growth when injected with both lung cancer cells and THC. However, the compound appeared to have no effect on mice whose immune systems were already compromised.

While previous research had shown that THC can lower resistance to both bacterial and viral infections, this is the first time that THC’s possible tumor-promoting activity has been reported, according to the National Institute on Drug Abuse, a part of the National Institutes of Health.

The UCLA scientists also found that the tar in marijuana smoke contains higher concentrations of substances called hydrocarbons than tar from tobacco smoke does. These hydrocarbons are a key factor in promoting human lung cancer.

Because marijuana smoke deposits four times as much tar in the respiratory tract as a comparable amount of tobacco, the exposure to carcinogens is increased, the researchers wrote.

"What we already know about marijuana smoke, coupled with our new finding that THC may encourage tumor growth, suggests that regular use of marijuana may increase the risk of respiratory-tract cancer and further studies will be needed to evaluate this possibility," Dr. Steven M. Dubinett, head of the research team that conducted the study, said in a statement.

Smoking marijuana is illegal in the United States, though several states have laws allowing its use for medicinal purposes. A federal advisory panel last year acknowledged that marijuana can fight pain and nausea, and the drug is thought to ease symptoms of the eye disease glaucoma.

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National Institute on Drug Abuse
Journal of Immunology
Marijuana

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