Article content continued

“It is seen as organic and natural,” he said. “[The study] does add one piece of evidence to suggest a caution around that.”

Other leading scientists in the field, however, say the nature of the data used in the new research, published in the journal Cancer Causes and Control, makes its findings suspect. Much more convincing evidence was analyzed recently by the International Lung Cancer Consortium, asserted Hal Morgenstern, a University of Michigan epidemiologist and part of that group.

The consortium scrutinized results from six “case-control” studies that compared 2,100 cancer patients and 3,000 healthy controls, finding no significant link between marijuana and malignancy, the scientists told a conference in April.

Though marijuana smoke does contain cancer-causing chemicals, the majority of people simply don’t consume enough of it to get ill, said Mr. Morgenstern.

“When you think about people smoking 20-40 cigarettes a day for 40 years, they’re smoking hundreds of thousands of cigarettes,” he said. “The exposure [to harmful smoke] that marijuana users get … is more than a magnitude of difference less.”

There are reasons to fear that smoking pot might lead to cancer, including the fact it contains some of the same carcinogens as tobacco, tends to be inhaled more deeply and generally is smoked without a filter.

‘It is seen as organic and natural. [The study] does add one piece of evidence to suggest a caution around that’

Meanwhile, use of medical marijuana is increasingly popular, with varying amounts of evidence suggesting it can help alleviate chemotherapy-related nausea, some forms of pain and loss of appetite in cancer patients.