SAN FRANCISCO — San Francisco became the first city in the United States to ban e-cigarettes Tuesday, a move that seeks to curb what experts have described as an nicotine epidemic among teenagers.

“We’ve worked for decades to decrease tobacco usage and try to end nicotine addiction,” said Shamann Walton, a member of the board of supervisors and a co-author of the bill banning e-cigarettes, which will go into effect 30 days after it is signed by the mayor. “Now you have this device loaded with nicotine and chemicals that’s drawing people to addiction. We need to keep it out of the hands of young people.”

Passage of the bill was praised by anti-tobacco advocates and the American Heart Association, among other health organizations.

But the bill also has many critics, including researchers who say they worry that a blanket ban on e-cigarettes could harm the wider goals of anti-tobacco efforts by eliminating what experts consider a safer alternative to conventional cigarettes.

Although they contain high levels of nicotine, which is highly addictive, e-cigarettes contain a fraction of the toxins that make conventional cigarettes the leading cause of preventable death in the United States.

Merchants will be allowed six months to deplete their stock, and the ban will not affect the sale of conventional cigarettes or cannabis joints.

“On the face of it, it’s ludicrous that we would ban e-cigarettes but permit the sale of tobacco and cannabis,” said Dr. Steven A. Schroeder, a professor of health at the University of California, San Francisco. “It’s really smart politics but dubious public health.”

Schroeder said the ban was likely to please San Francisco parents who were concerned that their children would “succumb to vaping.”

But conventional smokers tend to have lower incomes, and the ban, Schroeder and others argue, could eliminate the less harmful alternative.

“Who are the smokers who could benefit” from e-cigarettes, he said. “They are the downtrodden. The homeless, the HIV positive, substance abusers, prisoners, who have no constituency politically.”

San Francisco has a long history of using ordinances to push progressive causes, imposing bans on plastic straws, the sale of fur products and facial recognition technologies, to name a few. The city has taken a leading role in tobacco control, banning flavored tobacco and cigarette sales at pharmacies.

The leading manufacturer of e-cigarettes, Juul, is based in San Francisco and politicians in the city have been openly hostile to the company.

“I would not lose any sleep at all if Juul left,” Walton said. “I would help them pack up.”

The board of supervisors passed a separate bill Tuesday that would bar any e-cigarette company from renting space on company-owned land, a measure that would not affect Juul, which recently purchased a high-rise building in the city.

Dennis Herrera, the city attorney and a co-author of the bill, said the law would be in place until the federal Food and Drug Administration conducted a full-scale assessment of e-cigarettes.

In 2017, the agency delayed regulations for e-cigarette makers, saying that they had potential as a “lower-risk alternative.”

“It’s incumbent on local and state authorities to step in and make sure their young people are protected in light of the fact that the FDA has totally abdicated its responsibility and let this product come to market without doing the premarket review that they were mandated to do,” Herrera said.

The FDA has so far postponed its review. The agency did not respond to a request for comment.

Researchers agree that more studies are needed to determine the degree of harm that e-cigarettes pose. E-cigarettes contain a small battery and deliver nicotine through an aerosol mist.

Ken Warner, a professor emeritus at the University of Michigan and an expert on tobacco harm, said there was wide consensus among experts that e-cigarettes were less harmful than conventional ones, but the question was by how much.

Warner and others say e-cigarettes appear to be contributing to strong declines in the use of conventional cigarettes.

“We have this very big increase in quitting in the U.S.,” he said. “We need to keep our eye on the prize — which is the reduction in cigarette smoking. That’s what’s killing people.”

Neal L. Benowitz, one of the world’s leading experts on nicotine and a professor of medicine at the University of California, San Francisco, described the decision by the board of supervisors as “terrible.”

“It’s well intentioned, but the people who voted on it really didn’t hear the full story,” he said.

But Christine Chessen, a parent of three in San Francisco who has been an outspoken supporter of the ban, offered an alternative argument.

“There are so many young people, including one of my own, who are being affected by this,” she said of e-cigarettes. “They are having a very hard time quitting.

“These products are so discreet,” she said. “Students are hiding them in their backpacks. Parents and teachers cannot stay on top of it.”

This article originally appeared in The New York Times.