Medical marijuana poses cancer risk

Updated: 05 Jul 2009
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SAN FRANCISCO - IT MIGHT take Californians a puff or two to get their heads around an apparent contradiction recently enshrined in state law.


The same marijuana smoke that doctors can recommend to ease cancer patients' suffering must soon come with a warning saying it causes the disease.


State environmental regulators last month voted to place marijuana smoke on its list of hundreds of substances known to cause cancer. The decision could lead to warning signs in medical marijuana dispensaries and labels on packaged pot within a year.


A voter-approved measure made medical marijuana legal in California in 1996. Key backers included patients with serious illnesses such as cancer and AIDS who said pot helped them manage pain and nausea.


Medical marijuana advocates sought to downplay the significance of the state's decision, arguing researchers have long known that the smoke contains cancer-causing compounds.


'This does not mean in any way that those carcinogens that appear in smoked marijuana, smoked cannabis, have any kind of causal relationship to cancer,' said Kris Hermes, spokesman for Americans for Safe Access, a pro-medical marijuana group.


Regulators disagree. Scientists with the state's Office of Environmental Health Hazard Assessment reviewed 27 studies of the links between marijuana and cancer in humans. Though not all the studies showed a link, regulators found that 'marijuana smoke was clearly shown, through scientifically valid testing according to generally accepted principles, to cause cancer,' according to an agency statement.


Dr Thomas Mack, a University of Southern California epidemiologist and chairman of the committee, said the decision to list marijuana smoke as a cancer-causing substance should not surprise anyone.


'If you take a piece of vegetable material, a leaf, and burn it, you're going to get the type of compounds that cause cancer,' he said.


Marijuana smoke and tobacco smoke share 33 of the same cancer-causing compounds, according to agency scientists. Even so, the existing evidence is merely 'suggestive' of a link between marijuana and cancer in humans, Dr Mack said. Only in tests that subjected animals to ultrahigh doses of marijuana was the connection between the drug and cancer totally clear, he said.




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