The fact is, however, that no one knows how many more people will try marijuana if it becomes legal. Some experts predict a 50% increase while others say that the numbers are unlikely to rise because California's relaxed medical marijuana laws have already made the drug easy to obtain.
"It's a vast exaggeration that more people will take this up," said Stephen Gutwillig, California director of the Drug Policy Alliance, a national group that advocates for changes in the nation's approach to illicit drugs. Gutwillig supports legalization.
"The bottom line is that marijuana is far less dangerous than alcohol and cigarettes," Gutwillig added. "It's far less addictive than either of them. People tend to use marijuana in smaller amounts. It does not have alcohol's noxious association with violence and reckless behavior. And you can't overdose."
Members of the California Society of Addiction Medicine are divided on legalization. In a recent survey, more than two-thirds of the members believe there will be an increase in the amount of marijuana addiction if the drug were legalized. And close to 70% think there will be increased use by adolescents.
Though the association itself takes no position, its website lists controls that should be in place if the drug becomes legal.
Among them: creating restrictions to minimize minors' access to the drug; advertising and marketing rules; warning labels on marijuana products; use of fees and taxes from marijuana sales to fund marijuana addiction treatments; treatment instead of legal punishment for adolescent marijuana users; and periodic evaluation of the law for its effect on health and driving under the influence.
Cermak noted that Proposition 19 lacks many of these safeguards. Furthermore, he added, "If you read Proposition 19, the assertion is that it's not physically addictive and doesn't have long-term toxic effects on the body. We are asking people to memorialize the acceptance of those myths."
McDonald, who lives in Baldwin Hills, certainly didn't think marijuana was addictive. It had seemed so harmless. Inhaling from bamboo bongs made popular by returning Vietnam War vets, she began to feel some relief from the depression that had plagued her since youth.
But, with a $5,000-a-year habit and chronic bronchitis, she tried repeatedly to quit. About a dozen times over the years she checked in alone to a hotel in Desert Hot Springs to white-knuckle herself through nausea, sweats and tremors.
Short periods of abstinence were followed by relapses. She could barely get through her workdays, and her husband grew increasingly exasperated by her behavior.
At 42, after several months of abstinence, her depression without the drug was so great that she attempted to kill herself by taking "every pill in the house." She resumed smoking. Five years after the suicide attempt, she checked into a hospital rehab program.
"I finally decided I had to have help to quit," she said. "I smoked my last joint in the car on the way to St. John's Hospital with my head under the dashboard."
Even after what she went through, McDonald said she would like to see marijuana legalized so that people who have problems with the drug will be steered into treatment.
Even "as someone who has been far down the rabbit hole, I still don't think it's as dangerous as alcohol," she said. "But if I'd had any inkling of what it would do, I would have been more careful."