Posted on: Sunday, 5 July 2009, 10:30 CDT

In a move that has the good people of California scratching their heads in perplexity, state lawmakers recently passed a measure that would eventually require medical marijuana—prescribed most frequently to alleviate suffering in patients with severe cancer—to carry a warning label telling of its potential cancer-causing risks.

Last month state environmental regulators decided that cannabis should be added to its official list of substances known to cause cancer, which will likely lead to warning signs in marijuana dispensaries and cautionary labels on product packaging.  

In a 1996 referendum, Californians voted to legalize the leafy green stuff for patients ailing under serious diseases such as AIDS, cancer and glaucoma.  A number of research studies have pointed to the unique benefits of marijuana in counteracting the pain, nausea and “wasting-effect” that often accompanies the late stages of AIDS and cancer in particular.

Defenders of pot legalization have argued that scientists have long known that marijuana smoke contains carcinogens, but that this does not necessarily prove a causal relationship with cancer.

Regulators have countered this claim however, pointing to studies conducted by the state’s Office of Environmental Health Hazard Assessment in which "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 add marijuana smoke to the official list of cancer-causing substances is no big shocker.

“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,” explained Mack.

Still, Mack agrees to some extent with the defenders of marijuana legalization, saying that the data linking marijuana smoke to cancer is only “suggestive” and by no means conclusive.

Critics of the regulatory decision have pointed to a number of methodological flaws in the studies reviewed by the committee, such as the inclusion of data from studies conducted in North Africa, where marijuana is typically mixed with tobacco.

There is by no means a consensus in the scientific community regarding the relationship between pot smoke and cancer.  One 2006 study even indicated that marijuana smokers may actually be at a reduced risk of developing cancer than nonsmokers.

“If they want to classify marijuana smoke as carcinogenic, then that is true. It contains carcinogens,” said Donald Tashkin, a longtime marijuana researcher at the University of California. "That doesn't mean it causes cancer."

Ironically, the regulators’ authority to list marijuana as a cancer-causing substance derives from another voter-approved measure known as Proposition 65, which instructs state health officials to compile a list of all substances that can lead to cancer, birth defects or reproductive abnormalities.

First instituted in 1986, critics contend that the list of dangerous substances has grown absurdly long, including such common products as aspirin, gasoline, potato chips and French fries.

Dr. Frank Lucido of Berkeley, vice president of the American Academy of Cannabinoid Medicine, is a true believer in the benefits of medical marijuana and says that he has been prescribing it to patients since it first became legal in 1996.  The AACD is a recently formed organization of physicians who study and advise standards for medical marijuana use.

Lucido says that while he will not stop prescribing marijuana as a result of the legislation, he may begin suggesting that patients take it in a smoke-free form, such as marijuana-infused foods or vaporizers.

“Obviously, it's never good to breathe smoke if you can avoid it,” Lucido said.