In 1969, Carol McDonald was 28, married and the mother of two young children, out for an evening of fun with a couple who smoked marijuana. By the end of the evening she was on her way to a 19-year addiction.
"Within a few months, I was smoking every day," said McDonald, a retired bookkeeper, now 69. "I had to smoke before going to work. If something was upsetting, I smoked over it. If there was a celebration, I smoked over it."
People like McDonald may be largely overlooked in the statewide debate over legalizing marijuana. The drug has a benign reputation: Many baby boomers smoked and emerged unscathed, and medical marijuana facilities with their friendly images of seven-fingered leaves have popped up all over Los Angeles.
That might be why Proposition 19, the Nov. 2 ballot measure that would legalize marijuana and regulate it similarly to alcohol, has generated scores of reports and debates regarding the potential effect on business revenue, tax dollars and law enforcement but scant discussion on the potential fallout on people's health.
In California, addiction counselors are split on the legalization issue largely because of their long-standing support of treatment over jail and legal penalties for marijuana addicts. Yet nationally, public health experts mostly are against legalization. They say it will increase the number of people who become addicted to the drug, contribute to more automobile accidents and erode school performance.
"It's bizarre to me when people say, 'Make marijuana legal, and we'll have no problems with it,' " said Keith Humphreys, a professor of psychiatry and behavioral science at Stanford University who recently served as a White House senior advisor on the nation's drug control policy.
Because the science of marijuana's health effects is in many cases unclear, experts on each side of the legalization debate can point to scientific studies that support their own position.
They do agree that marijuana should be avoided during pregnancy and that it is harmful for people with mental illness or who are at risk for developing a serious mental illness, such as schizophrenia.
And they agree, too, on some basic statistics: Marijuana is addictive for about 9% of adults who use it (compared with about 15% who use alcohol and 15% who use cocaine), according to federal data. Because it is the most widely used illegal substance in the country, marijuana dependence is more common than addiction to either cocaine or heroin despite its lower addiction potential.
"We generally think the problems with marijuana aren't as serious as the problems you tend to see with cocaine or heroin," said Alan J. Budney, a leading researcher on marijuana at the Center for Addiction Research at the University of Arkansas for Medical Sciences who opposes legalization. "But they are still pretty substantial."
The science of marijuana becomes murky when one steps beyond addiction statistics to examine effects on health.
A series of studies conducted by the National Highway Traffic Safety Administration published in 1998 found that the effects of marijuana alone on driving were small or moderate, but severe when combined with alcohol.
But other studies show little impairment from a moderate dose: A 2004 study in the journal Accident, Analysis and Prevention found no increased risk of motor vehicle accidents causing traumatic injury among drivers using marijuana.
"Even after smoking, there aren't any real deficits in driving ability that we can detect in the laboratory," said Mitch Earleywine, an associate professor of psychology at the State University of New York at Albany who serves as an advisory board member at the National Organization for the Reform of Marijuana Laws.
The data on lung damage and smoking-related cancers are similarly mixed, in part because a large portion of heavy marijuana users also smoke tobacco, which muddies the picture of marijuana's effects. And though experts tend to agree that smoking marijuana causes short-term memory loss, they disagree widely on the overall cognitive effects of the drug.
Several studies have also dismissed the fear that marijuana is a "gateway" drug that will lead children and adolescents to experiment with harder illicit drugs — although numerous studies suggest that the earlier in life someone uses marijuana, the riskier it becomes. Among 14- and 15-year-olds who start to smoke, 17% will be dependent within two years, said Dr. Tim Cermak, an addiction psychiatrist and president of the California Society of Addiction Medicine.
The effect on school performance and learning could be significant if more minors use the drug, Cermak added. "Marijuana is not devastating in the same way alcohol is," he said. "But to an adolescent, it can impact their life permanently. When you take a vacation from development in school for five years, you just don't get to the same endpoint that was available to you earlier in life."
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."