LOS ANGELES — In the heart of Northern California’s marijuana growing region, the sheriff’s office is inundated each fall with complaints about the stench of marijuana plots or the latest expropriation of public land by growers. Its tranquil communities have been altered by the emergence of a wealthy class of marijuana entrepreneurs, while nearly 500 miles away in Los Angeles, officials have struggled to regulate an explosion of medical marijuana shops.
But at a time when polls show widening public support for legalization — recreational marijuana is about to become legal in Colorado and Washington, and voter initiatives are in the pipeline in at least three other states — California’s 17-year experience as the first state to legalize medical marijuana offers surprising lessons, experts say.
Warnings voiced against partial legalization — of civic disorder, increased lawlessness and a drastic rise in other drug use — have proved unfounded.
Instead, research suggests both that marijuana has become an alcohol substitute for younger people here and in other states that have legalized medical marijuana, and that while driving under the influence of any intoxicant is dangerous, driving after smoking marijuana is less dangerous than after drinking alcohol.
Although marijuana is legal here only for medical use, it is widely available. There is no evidence that its use by teenagers has risen since the 1996 legalization, though it is an open question whether outright legalization would make the drug that much easier for young people to get, and thus contribute to increased use.
And though Los Angeles has struggled to regulate marijuana dispensaries, with neighborhoods upset at their sheer number, the threat of unsavory street traffic and the stigma of marijuana shops on the corner, communities that imposed early and strict regulations on their operations have not experienced such disruption.
Imposing a local tax on medical marijuana, as Oakland, San Jose and other communities have done, has not pushed consumers to drug dealers as some analysts expected. Presumably that is because it is so easy to get reliable and high-quality marijuana legally.
Finally, for consumers, the era of legalized medical marijuana has meant an expanded market and often cheaper prices. Buyers here gaze over showcases offering a rich assortment of marijuana, promising different potencies and different kinds of highs. Cannabis sativa produces a pronounced psychological high, a “head buzz,” while cannabis indica delivers a more relaxed, lethargic effect, a “body buzz.”
Advocates for marijuana legalization see the moves in Colorado and Washington as the start of a wave. A Gallup poll released last week found that 58 percent of Americans think the drug should be made legal.
“There is definitely going to be a legalization here at some point, one way or another, like in Colorado and Washington,” said Tom Ammiano, a Democratic state assemblyman from San Francisco who has pushed the Legislature to legalize recreational marijuana use.
Still, even as public opinion in support of legalizing marijuana has grown, opposition remains strong among many, including some law enforcement organizations, which warn that the use of the drug leads to marijuana dependence, endangers the health of users and encourages the use of other drugs.
“Unfortunately, many have been convinced that marijuana is harmless, and many in policing do not believe that is the case,” Darrel W. Stephens, the executive director of the Major Cities Chiefs Association, wrote in an e-mail.
Craig T. Steckler, a former chief of the Police Department in Fremont, Calif., who is now the president of the International Association of Chiefs of Police, said the problems in Los Angeles and robberies of cash-rich marijuana farms in Northern California were just two of the reasons states should hesitate before legalizing the drug.
“If it’s more readily accessible, if the parents and the siblings are doing it, then it becomes available to the younger kids — it’s going to be in the house, it’s going to be in the car,” he said.
“Where does it stop?” Mr. Steckler asked. “You make all drugs legal? Or just marijuana for now and suffer for that? What happens when you find out this wasn’t such a good idea?”
After California, medical marijuana was legalized in 19 states and the District of Columbia, according to the National Conference of State Legislatures.
Although the law in California applies only to people who have a medical need for marijuana, like glaucoma or cancer, the requirements for getting the card to buy the drug are notoriously lax. Doctors can recommend its use for ailments as common as sleeplessness and headaches. And marijuana in California has become almost as culturally accepted, and in some parts of the state nearly as widely used, as alcohol.
“Marijuana users are much more representative of the overall adult population in California than medical marijuana populations in other states,” said Amanda Reiman, the state policy director for the Drug Policy Alliance, an organization working toward the decriminalization of marijuana.
The percentage of California drivers with traces of marijuana in their systems, 14 percent, was found to be nearly double that of people with alcohol during a spot check last year, according to a report from the California Office of Traffic Safety.
In a broad study on the ramifications of legalizing recreational marijuana about to be published in The Journal of Policy Analysis and Management, two economics professors said a survey of evidence showed a correlation between increased marijuana use and less alcohol use for people ages 18 to 29.
The researchers, D. Mark Anderson of Montana State University and Daniel I. Rees of the University of Colorado, said that based on their study, they expected younger people in Colorado and Washington to use marijuana more and alcohol less.
“These states will experience a reduction in the social harms resulting from alcohol use: Reducing traffic injuries and fatalities is potentially one of the most important,” the professors said.
Mark A. R. Kleiman, a professor at the University of California, Los Angeles, and an expert on marijuana policy who was the chief adviser to Washington on its marijuana law, said the connection between alcohol and marijuana use, if borne out, would be a powerful argument in favor of decriminalization.
“If it turns out that cannabis and alcohol are substitutes, then by my scoring system, legalizing cannabis is obviously a good idea,” Mr. Kleiman said. “Alcohol is so much more of a problem than cannabis ever has been.”
Still, he said, it will take time before long-term judgments can be made.
“Does it cause problems?” he said. “Certainly. Is it on balance a good or bad thing? Ask me 10 years from now.”
Mr. Rees also said his study found no evidence of increased drug use among high school students in Los Angeles during the period when medical marijuana shops opened here, probably because dispensaries were vigilant about not risking their thriving ventures by selling to under-age consumers.
“The dispensary numbers went through the roof,” he said. “But nothing happens to marijuana use among teenagers.”
The marijuana cultivation business in Northern California has been an economic boon for many communities, creating tax revenues, an industry of ancillary industries, and local wealth, visible by expensive cars parked along once dusty streets.
“A lot of cottage industries have popped up that service the marijuana industry,” said Scot Candell, a lawyer in San Rafael who specializes in medical marijuana clients. “Labs that do testing, hydroponic stores that provide growing equipment, software developers, insurance companies that specialize in dispensaries.”
Steve DeAngelo, the founder of the Harborside Health Center in Oakland, one of the state’s largest marijuana dispensaries, said his dispensary collected $1.2 million last year in marijuana sales tax for the city.
Medical marijuana, he said, has “created a whole new cast of people who have a vested interest in cannabis.”
“What was inevitable is that the movement, at some point, would go into hyper-speed, and that is what’s happening now,” he said.
This has altered the economy of places like Mendocino County.
“I am not aware of any business in Mendocino County that doesn’t consider marijuana as part of their business plan, and that can be good and bad,” said Sheriff Thomas D. Allman.
Mr. Candell said that while regulation was important, overregulation could be counterproductive. In California, several communities outlawed all marijuana dispensaries, giving rise to delivery services, which are not subject to regulation.
In Mendocino the issue is not dispensaries, but cultivation. There has been a spectacular rise in the amount of marijuana being grown there because, under county law, individuals with medical marijuana cards can have up to 25 plants for personal use.
Sheriff Allman said he spent about 30 percent of his resources on medical marijuana cases, especially between April and October, the growing season. The No. 1 call to 911 in October is complaints about the overwhelming smell of a next-door plot.
In Los Angeles, repeated attempts to regulate the stores have failed, causing an uproar in quiet neighborhoods like Larchmont and Mar Vista. Yet there is a lesson here: San Francisco, Oakland and Berkeley, which imposed strict regulations on the shops from the start, have had few problems.
“Those cities really took charge in 1996, saying: ‘We have to figure out how we are going to regulate this. We need to figure out how marijuana could be sold, how it will be regulated, what it will mean for tax revenue,’ ” Ms. Reiman said. “As a result, those three cities have seen little to no issues in terms of crime or public safety issues.”
Consumers of marijuana are also benefiting. Competition among growers has resulted in powerful strains, raising the levels of THC, the active ingredient in marijuana, to as high as 25 percent. Previously, levels ranged from 6 percent to 9 percent.
And since cities have competing dispensaries, prices have tended to decrease or at least keep pace with street prices. At Harborside in Oakland, marijuana buds run anywhere from $240 to $360 an ounce, though patients tend to buy smaller amounts like an eighth or a quarter of an ounce.
The array of products has exploded, and now includes not only smokable buds but also hashish, marijuana-rich oils that are drunk or smoked, edible cakes and other food products, and topical ointments intended to ease skin or joint pain without providing a high.
California has learned a lot in its years of dealing with a legal form of marijuana, Mr. Candell said. “But there are a lot of states that are just now going through it, and there are things they need to know.”