Tuesday, 26 October, 2021
HomeHarm ReductionBan on flavoured vaping may have led teens to cigarettes — Yale...

Ban on flavoured vaping may have led teens to cigarettes — Yale study

After San Francisco banned flavoured vaping, the odds of high school students smoking cigarettes doubled, according to Yale University. There is a need to weigh the harms of vaping against the greater harms of smoking, or a law could inadvertently increase youth smoking and pose a threat to public health, writes Assistant Professor Abigail Friedman.

The following material, written by Michael Greenwood, was published in Yale News by Yale University on 25 May 2021.

When San Francisco voters overwhelmingly approved a 2018 ballot measure banning the sale of flavoured tobacco products – including menthol cigarettes and flavoured vape liquids – public health advocates celebrated. After all, tobacco use poses a significant threat to public health and health equity, and flavours are particularly attractive to youth.

But according to a new study from the Yale School of Public Health (YSPH), that law may have had the opposite effect.

Analyses found that, after the ban’s implementation, high school students’ odds of smoking conventional cigarettes doubled in San Francisco’s school district relative to trends in districts without the ban, even when adjusting for individual demographics and other tobacco policies.

The study, published in JAMA Pediatrics on 24 May, is believed to be the first to assess how complete flavour bans affect youth smoking habits.

“These findings suggest a need for caution,” said Abigail Friedman, the study’s author and an assistant professor of health policy at YSPH.

“While neither smoking cigarettes nor vaping nicotine are safe per se, the bulk of current evidence indicates substantially greater harms from smoking, which is responsible for nearly one in five adult deaths annually. Even if it is well-intentioned, a law that increases youth smoking could pose a threat to public health.”

Friedman used data on high school students under 18 years of age from the Youth Risk Behavior Surveillance System’s 2011-2019 school district surveys. Prior to the ban’s implementation, past-30-day smoking rates in San Francisco and the comparison school districts were similar and declining.

Yet once the flavour ban was fully implemented in 2019, San Francisco’s smoking rates diverged from trends observed elsewhere, increasing as the comparison districts’ rates continued to fall.

To explain these results, Friedman noted that electronic nicotine delivery systems have been the most popular tobacco product among United States youth since at least 2014, with flavoured options largely preferred.

“Think about youth preferences: some kids who vape choose e-cigarettes over combustible tobacco products because of the flavours,” she said. “For these individuals as well as would-be vapers with similar preferences, banning flavours may remove their primary motivation for choosing vaping over smoking, pushing some of them back toward conventional cigarettes.”

These findings have implications for Connecticut, where the state legislature is currently considering two flavour bills: House Bill 6450 would ban sales of flavoured electronic nicotine delivery systems, while Senate Bill 326 would ban sales of any flavoured tobacco product.

As the US Food and Drug Administration recently announced that it will ban flavours in all combustible tobacco products within the next year, both bills could result in a Connecticut policy that is similar to the complete ban enacted in San Francisco.

The San Francisco study does have limitations. Because there has been only a short time since the ban was implemented, the trend may differ in coming years. San Francisco is also just one of several localities and states that have implemented restrictions on flavoured tobacco sales, with extensive differences between these laws. Thus, effects may differ in other places, Friedman wrote.

Still, as similar restrictions continue to appear across the country, the findings suggest that policymakers should be careful not to indirectly push minors toward cigarettes in their quest to reduce vaping, she said.

What does she suggest as an alternative? “If Connecticut is determined to make a change before the FDA’s flavour ban for combustible products goes into effect, a good candidate might be restricting all tobacco product sales to adult-only – that is 21-plus – retailers,” she said.

“This would substantively reduce children’s incidental exposure to tobacco products at convenience stores and gas stations, and adolescents’ access to them, without increasing incentives to choose more lethal combustible products over non-combustible options like e-cigarettes.”

This work was supported by a grant from the National Institute on Drug Abuse of the National Institutes of Health and FDA Center for Tobacco Products. The content is solely the responsibility of the author and does not necessarily represent the official views of the National Institutes of Health or the Food and Drug Administration.


Research Letter 

A Difference-in-Differences Analysis of Youth Smoking and a Ban on Sales of Flavoured Tobacco Products in San Francisco, California

Abigail S Friedman

Author affiliation: Department of Health Policy and Management, Yale School of Public Health.

Published by JAMA Pediatrics on 24 May 2021



Restrictions on flavoured tobacco product sales are increasingly popular; five US states and hundreds of localities have implemented them in the past few years alone.

Yet only one study, to my knowledge, has considered how complete flavour bans applying to electronic nicotine delivery systems and combustible tobacco products, without retailer exemptions, are associated with tobacco use.

A convenience sample of residents of San Francisco, California, aged 18 to 34 years who had ever used a tobacco product showed significant reductions in any tobacco use following the city’s flavour ban, with a marginally significant increase in combustible cigarette use (smoking) among those aged 18 to 24 years.

Absent a comparison group, however, it is impossible to ascertain if pre-existing trends could have driven these findings.

Given the relative health costs of smoking vs vaping nicotine, flavour bans that increase smoking may prove harmful. Thus, this study’s objective was to estimate the association between San Francisco’s ban on flavoured tobacco product sales and smoking among high school students younger than 18 years.


Data came from the 2011-2019 Youth Risk Behavior Surveillance System (YRBSS) biennial school district surveys, with consideration restricted to districts with representative smoking data (with response rates ≥60%) available through the US Centers for Disease Control and Prevention for each wave: New York City, New York; Broward County, Florida; Los Angeles, California; Orange County, Florida; Palm Beach County, Florida; Philadelphia, Pennsylvania; and San Diego, California, as well as San Francisco, California.

This analysis focused on high school students younger than 18 years who had nonmissing data for the outcome of interest: a binary indicator for recent (ie, past 30-day) smoking. This study was deemed exempt from institutional review board review under US federal regulation 45 CFR 46.101(b)(4).

The analysis used publicly available YBRSS data, a survey with collection procedures designed to maintain student anonymity; therefore, informed consent was not required.

A binary exposure variable captured whether a complete ban on flavoured tobacco product sales was in effect in the respondent’s district on January 1 of the survey year. (The YRBSS is fielded during the spring semester and does not report interview dates; further details are in the eMethods in the Supplement).

Recent vaping was not considered because of likely confounding. California legalised recreational marijuana use the same year San Francisco’s flavour ban went into effect; in addition, the YRBSS’s vaping questions did not distinguish vaping nicotine vs marijuana.

Covariates captured age, sex, and race/ethnicity fixed effects and tobacco policies on January 1 of the survey year (specifically, state-plus-district conventional cigarette taxes and indicators for smoke-free restaurant laws). San Francisco did not implement other new tobacco control policies between the 2017 and 2019 surveys.

To compare trends, annual sample-weighted means and 95% CIs were plotted for recent smoking in San Francisco vs other districts. Difference-in-differences analyses used logistic regressions to estimate changes in recent smoking in San Francisco relative to other districts, before vs after the flavour ban’s implementation, adjusting for year and district fixed effects alongside the aforementioned demographic and policy covariates.

Robustness checks further adjusted for district-specific time trends and considered California districts only, to ensure uniform state policy exposure. Two-tailed P values less than .05 were considered significant. Data were analyzed from February 2021 to March 2021 using Stata version 14 (StataCorp).


The data set yielded an analytic sample of 100 695 minors, 95,843 of whom had nonmissing data on recent smoking. Among those with data, 9,225 respondents came from San Francisco vs 86,618 from other districts, with weighted means indicating smoking rates of 6.2% (95% CI, 5.2%-7.1%) and 5.6% (95% CI, 5.3%-5.9%), respectively.

Comparing recent smoking rates by wave revealed similar trends in San Francisco vs other districts prior to 2018 but subsequent divergence (2019: San Francisco, 6.2% [95% CI, 4.2%-8.2%]; other districts, 2.8% [95% CI, 2.4%-3.1%]). Difference-in-differences analyses found that San Francisco’s flavour ban was associated with more than doubled odds of recent smoking among underage high school students relative to concurrent changes in other districts (adjusted odds ratio, 2.24 [95% CI, 1.42-3.53]; P = .001).

This result was robust to adjustment for district-specific time trends (adjusted odds ratio, 2.32 [95% CI, 1.45-3.70]; P < .001) and limiting consideration to California (adjusted odds ratio, 2.01 [95% CI, 1.15-3.51]; P = .01).


San Francisco’s ban on flavoured tobacco product sales was associated with increased smoking among minor high school students relative to other school districts. While the policy applied to all tobacco products, its outcome was likely greater for youths who vaped than those who smoked due to higher rates of flavoured tobacco use among those who vaped.

This raises concerns that reducing access to flavoured electronic nicotine delivery systems may motivate youths who would otherwise vape to substitute smoking. Indeed, analyses of how minimum legal sales ages for electronic nicotine delivery systems are associated with youth smoking also suggest such substitution.

This study’s primary limitation is generalisability. Future research should assess whether estimates hold over time and in other localities and consider how policy heterogeneity (eg, retailer exemptions) modifies such bans’ outcomes.



Yale University material – Ban on flavoured vaping may have led teens to cigarettes, study suggests (Open access)

JAMA Pediatrics article – A Difference-in-Differences Analysis of Youth Smoking and a Ban on Sales of Flavoured Tobacco Products in San Francisco, California




‘Misguided’ push to outlaw vaping in developing nations

San Francisco needs to admit it was wrong about vaping ban

Calls for vaping products to have health messages – and separate regulations

E-cigarette use plummets among American youth – FDA survey

Canadian youth are vaping early and often – Heart and Stroke Foundation

Amid youth vaping ‘epidemic’, adolescent smoking hits record low

Advertising restrictions needed to curb vaping among youth




Subscribe to our Newsletter

Receive Medical Brief's free weekly e-newsletter.

* indicates required