- Los Angeles, CA
- Heather Burke, Bloomberg News
- Seattle Post-Intelligencer (seattlepi.newsource.com)
Marijuana smoke thought to be similar to tobacco
People who smoke marijuana may be at less risk of developing lung cancer than tobacco smokers, according to a new study.
The study of 2,200 people in Los Angeles found that even heavy marijuana smokers were no more likely to develop lung, head or neck cancer than non-users, in contrast with tobacco users, whose risk increases the more they smoke.
The findings are a surprise because marijuana smoke has some of the same cancer-causing substances as tobacco smoke, often in higher concentrations, said the senior researcher, Donald Tashkin, a professor at the David Geffen School of Medicine at the University of California-Los Angeles.
One possible explanation is that THC, a key ingredient in marijuana not present in tobacco, may inhibit tumor growth, he said in an interview.
“You can’t give marijuana a completely clean bill of health,” said Tashkin, who is to present the study to a conference of the American Thoracic Society. “I wouldn’t give any smoke substance a clean bill of health. All you can say is we haven’t been able to confirm our suspicions that marijuana might be a risk factor for lung and head and neck cancer.”
About 1,200 adults under age 60 with cancer of the lung, tongue, mouth, throat or esophagus, took part in the study, as well as about 1,000 without cancer, between 1999 and 2003.
Marijuana use was found to be no greater or less in any of the groups — 44 percent of those with lung cancer, 41 percent with head or neck cancers, and 42 percent of those without cancer, said Tashkin.
Other studies had suggested marijuana smoking was a risk factor for cancer, Tashkin said. Marijuana smokers inhale more deeply than tobacco smokers and often hold the smoke in their lungs more than four times longer, depositing more tar, he said.
The results of Tashkin’s study confirm some earlier research, said Paul Armentano, a senior policy analyst at the National Organization for the Reform of Marijuana Laws, which advocates legalizing marijuana use.
“It’ll be surprising results in light of the way marijuana has been presented for many years by the government and the media, as a cancer-causing agent,” Armentano said.
Dr. Bertha Madras, deputy director for demand reduction at the White House’s drug policy office, said she couldn’t directly comment on the study without seeing the details.
“There is strong evidence that chronic marijuana use can lead to adverse effect on lung function such as increased bronchitis and lung inflammation,” Madras said.
The study was funded by the National Institute on Drug Abuse, Tashkin said.