Long term or heavy use of marijuana does not cause lung or neck cancers even though marijuana produces more resin and tar than tobacco, a study, by researchers from the David Geffen School of Medicine in the University of California, has found. The study also absolved marijuana of all blame in tongue, mouth, throat and esophageal cancers.
Under the study, the researchers took into account the marijuana use of 2,252 subjects under the age of 60. Of these, 611 suffered from lung cancer, 601 had cancer in neck or head, and 1,040 were free of the malignancy. The subjects were asked a series of questions including those about the amount of marijuana they smoked, their diets, family health history, occupation and use of tobacco and alcohol. Those who had smoked over 22,000 marijuana joints were classified under heavy smokers, while those whose count fell between 11,000 and 22,000 joints were categorized as moderately heavy smokers. Some did not smoke marijuana at all.
“We expected that we would find that a history of heavy marijuana use – more than 500-1,000 uses - would increase the risk of cancer from several years to decades after exposure to marijuana,” said Dr Donald Tashkin, who led the study. However, the team surprisingly found no link between use of marijuana and cancers. “We know that there are as many or more carcinogens and co-carcinogens in marijuana smoke as in cigarettes. But we did not find any evidence for an increase in cancer risk for even heavy marijuana smoking,” he said.
According to Tashkin, one explanation might be that Delta9-Tetrahydrocannabinol (THC), which is found in marijuana smoke, causes the death of old cells faster. Due to this, these cells do not become cancerous. One result of the study was that those who smoked two or more packs of cigarettes were 20 times more susceptible to lung cancer than those who didn't.
The researchers, however, warned against increasing use of marijuana in the wake of the results. Marijuana contains as much as 50 per cent more tar than tobacco does and can cause long-term damage to the lungs because it is inhaled deeper, Tashkin said. “Marijuana is packed more loosely than tobacco, so there's less filtration through the rod of the cigarette, so more particles will be inhaled. And marijuana smokers smoke differently than tobacco smokers – they hold their breath about four times longer, allowing more time for extra fine particles to deposit in the lung,” he said. Using the weed to lessen the risk of cancer also was not a good idea. “We saw no interaction between marijuana and tobacco, and we certainly would not recommend that people smoke marijuana to protect themselves against cancer,” Tashkin said.
Philadelphia's University of Pennsylvania Health System expert John Hansen-Flaschen said the findings should not be seen as a go-ahead to smoke marijuana, which can cause chronic bronchitis and even cognitive problems.
The findings of the study were presented at the American Thoracic Society meeting in San Diego on Tuesday.
