A California state board called marijuana smoke a health hazard and has added it to the state’s list of environmental hazards, placing the drug alongside other carcinogens like arsenic, asbestos, and DDT, the San Jose Mercury News reported June 19.

Scientists at California’s Office of Environmental Health Hazards Assessment (OEHHA) studied research that linked marijuana smoke to different types of cancer, in particular head and neck cancers, concluding that marijuana smoke contains many of the harmful properties found in tobacco smoke.

“There’s not one single piece of evidence that was a slam dunk,” said George Alexeeff,? Ph.D., deputy director for scientific affairs for the OEHHA. “But the pieces together form a very compelling argument.”

California medical-marijuana dispensaries with 10 or more employees will be required to post a warning label in their shop or on the products saying, “Contents may cause cancer when smoked.”

While marijuana smoke is now on California’s Prop. 65 list, the labeling requirements will not go into effect until June 19, 2010.

Assemblyman Tom Ammiano, who has sponsored legislation to legalize and tax marijuana in California, called the board’s singling out of marijuana “gratuitous,” while other marijuana-reform advocates expressed concern that the OEHHA findings would provide ammunition to opponents of legalization and decriminalization.