May 8, 2000 (Boston) -- Marijuana, unlike tobacco and alcohol, does not appear to cause head, neck, or lung cancer, says a researcher from Johns Hopkins Medical School in Baltimore who presented findings from a study here recently at a meeting of internal medicine physicians.
There has been an ongoing debate about whether marijuana is as dangerous as tobacco in terms of cancer development. Daniel E. Ford, MD, tried to sort out the evidence by the lifestyles -- including marijuana, tobacco, and alcohol use -- of 164 persons who were newly diagnosed with head, neck, or lung cancer compared to a group of 526 healthy persons living in the same area. The average age of patients was 49, while the average age of the healthy volunteers was 44. The cancer patients were all treated at four Baltimore-area hospitals, and the "controls" (healthy comparison group) were selected from a large group of people living in the Baltimore area who had been participating in an ongoing study. Ford tells WebMD that he wanted to find out whether the cancer patients were more likely to smoke marijuana or tobacco or to drink than were the healthy volunteers.
According to Ford, he thought he would find an association between marijuana use and cancer, but "that the association would fall away when we corrected for tobacco use. That was not the case. The association was never there." And that surprised him because of the way marijuana is smoked: deep inhalations, with the smoke held in for effect. "It seemed natural that there would be some connection," he tells WebMD.
Based on these findings, Ford says that cancer prevention efforts should "remain focused on tobacco and alcohol, two known carcinogens."
He says his conclusions differ from another study reported recently. That study linked marijuana use to cancer, but Ford says he thinks the difference can be explained by the fact that the healthy volunteers in that study "had very, very low use of marijuana." That contrasts to his study, in which "we were investigating the effect of marijuana as it is commonly used in the community," he says. Use of all substances -- tobacco, alcohol, and marijuana -- was common among both cancer patients and controls, he says.
"We attempted to assess both lifetime and current use of substances," he says. Participants were also asked to differentiate between use of marijuana cigarettes, marijuana pipes, or consumed marijuana. Distinctions were also made between weekend and weekday use of marijuana, he says.
"Ever use of marijuana was 66% among controls and 60% among the cases," he says. "Daily marijuana use for a month or more was not associated with increased risk, nor was age at first use, depth of inhalation, or use of a pipe." Surprisingly, using marijuana was not associated with increased cancer risk, even among those who never used tobacco, he says.
During the discussion period after the presentation, several people suggested that lack of quantity may explain why no association was found, because the number of marijuana cigarettes smoked is much lower than the number of tobacco cigarettes smoked. "It is true that we can't really correlate pack-years," says Ford, "and it should be noted that about 30% of the marijuana smokers never smoke cigarettes."
While this study suggests that marijuana has no link to head, neck, and lung cancer, a multicenter study released in March at an American Heart Association meeting linked marijuana use to increased risk of heart attacks. Murray A. Mittleman, MD, PhD, director of cardiovascular epidemiology at Beth Israel-Deaconess Hospital in Boston, told WebMD that marijuana smokers experience a 4.8-fold increase in the relative risk of heart attack during the first hour after smoking. The risk returns to normal after an hour, he said.
- New research shows that marijuana use is not associated with an increased risk of head, neck, or lung cancers.
- One researcher argues that cancer prevention efforts should remain focused on tobacco and alcohol, both known carcinogens.
- Although there is no evidence that marijuana smoking increases the risk of cancer, studies have shown that marijuana smokers have a nearly five-fold increased risk of having a heart attack during the first hour after smoking.