(CNN) Seeking to " curb the epidemic of youth vaping ," San Francisco officials voted on Tuesday to effectively ban the sale of e-cigarettes -- becoming the first US city to do so and thrusting the coastal tech hub into a fierce debate over the future of smoking.

Advocates of the ban say the city must act where federal regulators have not, protecting teens and prohibiting the sale of untested products until they undergo FDA review. Opponents say the new law leaves cigarettes -- known to cause cancer and heart disease -- as the only practical option for those addicted to nicotine.

But will the strict new policy make San Francisco healthier?

It depends on which public health experts you ask.

E-cigarettes are popular with smokers trying to kick the habit, as they satisfy the urge for nicotine while removing exposure to the tar and toxins of burned tobacco, but many worry they're creating new addictions to nicotine -- particularly among young people

Influential groups have backed the measure, including the American Lung Association and the American Heart Association. Others, such as the American Cancer Society, have declined to take a position.

And while some researchers see the ban as a useful experiment in tobacco control, others think the law will hurt the very teens it seeks to help.

Jamie Hartmann-Boyce, a senior researcher in health behaviors at the University of Oxford, said the debate is often framed, "Do we protect young people from becoming addicted to nicotine, or do we help people already addicted to nicotine switch to a safer alternative?"

But the reality is more complex, she said, and doesn't have to pit adults against teens: "There should be opportunities for balanced policies which address both priorities, and acknowledge that transitioning adult smokers to vaping also has the potential to protect the health of future generations."

'An important test case'

Nobody quite knows how San Francisco's e-cigarette policy will play out, and researchers will be watching closely to see what effect, if any, it has on rates of vaping and smoking in adults and teens.

"Throughout the history of the tobacco control movement, cities and localities have served as laboratories to see what measures will be most effective to reduce the death and disease caused by tobacco," said Lindsey Freitas, senior director of advocacy for the American Lung Association of California.

The law doesn't directly ban the sale of e-cigarettes. Instead, it mandates that any products be evaluated by the FDA before being sold in a process known as premarket review. Because no manufacturers have done that yet, the law will halt all vape sales in about seven months

"The e-cigarette companies have been aware of the FDA's intent for premarket review going back to 2016," said Jodi Prochaska, an associate professor of medicine at Stanford University. Vape manufacturers, she said, "have the resources financially and legally to navigate that process."

Prochaska called the new law "an important test case" and said San Francisco was the ideal city to test the new policy as a sort of "natural experiment."

The city's relatively low cigarette smoking rate -- just 11% among adults -- means that "there is little need for a 'harm reduction' nicotine approach here," said Prochaska, referring to claims that e-cigarettes should remain legal as a safer alternative to cigarettes. Universal health care in the city, provided to the uninsured through a program called Healthy San Francisco , means those who want to quit smoking can access tobacco addiction treatment, she added.

'The thing that we have all feared the most'

Dr. Robert Jackler, founder of the group Stanford Research Into The Impact of Tobacco Advertising, doesn't believe San Francisco's new law is good policy -- but not because of concern for adult smokers looking to switch.

"As a person who's an advocate for public health, if I had to weigh a choice between protecting young people from becoming nicotine-addicted, or helping adult smokers quit, I would always, first and foremost, configure policies to help young people."

In part, Jackler said, that's because the best way to eventually eliminate smoking in adults is to prevent teenagers from becoming addicted in the first place. But Jackler, whose research group has tracked thousands of e-cigarette advertisements seemingly targeting teens , says that a generation of young people are already hooked on nicotine.

San Francisco's ban is "misguided," he said, because banning vapes gives young people no other choice than to turn to tobacco, "the thing that we have all feared the most." While it's already illegal for those under 21 to buy e-cigarettes in California, a recent study found that half of tobacco and vape shops in the state don't ID teenagers.

Instead of driving those teens to products like cigarettes or hookah, Jackler favors limiting vape flavors, restricting the amount of nicotine in e-liquids, and increasing taxes on e-cigarettes to discourage use.

Is cigarettes vs. vapes a 'false dilemma'?

Juul Labs, the country's largest vape manufacturer, said in a statement Tuesday that "this full prohibition will drive former adult smokers who successfully switched to vapor products back to deadly cigarettes, deny the opportunity to switch for current adult smokers, and create a thriving black market instead of addressing the actual causes of underage access and use."

But Lauren Lempert, a law and policy specialist at University of California, San Francisco's Center for Tobacco Control Research and Education, said that opponents of the new law have created a "false dilemma." Cigarettes will not be the only option for smokers after the law goes into effect, she said, citing smoking cessation drugs and nicotine replacement therapy.

In any case, Lempert said, "e-cigarettes have not been approved by the FDA for cessation, and have not been determined to be a 'safer choice.' That is a presumption that underlies many of Juul's statements, but it has not been proven."

Undergoing FDA review, which the new San Francisco law demands, would require companies like Juul to provide data to back up their marketing claims, said Lempert. But cigarettes, known to harm human health, would not be affected.

"It's a fair question to ask why there are still legal cigarettes, which may be at least as dangerous, and possibly more dangerous [than vape products]," said Lempert. "But that doesn't mean you shouldn't at least address this immediate problem of e-cigarettes, and then if you want to move on from there and ban all tobacco products, then do that."

Banning cigarettes was once unthinkable in decades past, when smoking was legal in planes and restaurants. Now, an increasing number of Americans -- 1 in 4 -- believe that smoking in the United States should be illegal, up from 12% in 2007, according to a Gallup poll last year.

'This has not been tried before'

Cigarette smoking is the leading preventable cause of death in the United States, according to the US Centers for Disease Control and Prevention , and causes 480,000 deaths every year. Anything that can reduce those deaths, vape advocates say, is a win for public health.

study published this year, for example, found that e-cigarettes were almost twice as effective at helping smokers quit cigarettes than traditional nicotine-replacement therapy, such as nicotine patches. But 82% of people who vaped didn't quit smoking after a year. Among those who did quit cigarettes, 80% continued vaping.

That's consistent with other research on "dual users," which suggests that vaping may temporarily lead to lower cigarette consumption without convincing users to quit smoking entirely. One study published in 2017, for example, found that a majority of dual users abandoned e-cigarettes and continued to smoke only tobacco after two years.

And while smoking fewer cigarettes may reduce exposure to cancer-causing chemicals , new research also suggests that vapes can pose significant long-term risks to heart and lung health.

study published this year in the Journal of the American Heart Association, for example, found that vaping and smoking were both linked to a similar increase in the risk of heart attacks. Using both, the study found, was riskier than using either alone.

High school juniors and seniors in the United States who vaped were almost twice as likely to develop symptoms of chronic bronchitis than their peers, another study found. And a similar study in South Korea reported that high schoolers who vaped were more likely to have symptoms of asthma and miss school.

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Perhaps most troubling for tobacco control advocates, though, is evidence that e-cigarettes may serve as a gateway to smoking for young people. A study published this year, for example, found that teens who used e-cigarettes were more than four times as likely to try cigarettes than those who never vaped.

San Francisco's city attorney, Dennis Herrera, echoed those concerns after San Francisco's law passed on Tuesday afternoon. "This is a decisive step to help prevent another generation of San Francisco children from becoming addicted to nicotine," he said.

Whether Herrera is right remains to be seen. But one thing is clear to experts like Prochaska, who have studied tobacco for years: "This has not been tried before."