Researchers compared teen and young adult smoking patterns before and three years after a 2016 California law that increased the legal age for tobacco sales from 18 to 21.
The University of California, Davis team found that the "T21" law led to a greater decrease in daily smoking among those ages 18-20 than among those ages 21-23.
"The great news is that the prevalence of 'daily' smoking among 18- to 20-year-olds went from 2.2% in 2016 to nearly zero in 2019," said study co-author Susan Stewart, a professor in the division of biostatistics in the Department of Public Health Sciences.
There was no decrease in non-daily smoking.
"A possible reason that we may have seen a decrease in 'daily' smoking, but not 'non-daily' smoking, is that 'daily' smokers are more likely to buy their own cigarettes -- so they are more likely to be impacted by sales restrictions," Stewart said in a university news release.
Also, there was no decline in rates of people who were current smokers or who ever smoked, according to the study, which was published recently in the journal Preventive Medicine.
The researchers said possible reasons why there wasn't a drop in all types of smoking behavior after the law include: previous declines in smoking nationwide; enforcement difficulties at the state level; increased use of other products such as e-cigarettes and marijuana; sales outside of retail stores; and other tobacco control policies.
"Most adult tobacco users start smoking cigarettes before the age of 18, when the brain is still developing and is especially susceptible to nicotine and addiction," said study author Melanie Dove, an assistant professor in the division of health policy and management in the Department of Public Health Sciences.
"The new T21 law has the potential, over time, of dramatically reducing the number of youth who begin smoking regularly and that's why it is important to track the impact," Dove said in the release.
"Future studies should examine the role of e-cigarette use, policy enforcement, as well as online sales," said study co-author Dr. Elisa Tong, an internist and associate professor who directs tobacco cessation initiatives at the UC Davis Comprehensive Cancer Center.
The U.S. Centers for Disease Control and Prevention has more on youth tobacco prevention.
SOURCE: University of California, Davis, news release, April 23, 2021