In a study published in the American Journal of Public Health, UCSD researchers found that smokers who used e-cigarettes -- also known as vapor inhalers -- were 49 percent less likely to decrease cigarette use and 59 percent less likely to quit altogether, compared to smokers who never used e-cigarettes.
The population-based study followed 1,000 California smokers over one year, according to UCSD. The results come amid a debate over the effectiveness of the battery-operated devices.
"Based on the idea that smokers use e-cigarettes to quit smoking, we hypothesized that smokers who used these products would be more successful in quitting," said Dr. Wael Al-Delaimy, a professor and chief of the Division of Global Public Health in the Department of Family Medicine and Public Health.
"But the research revealed the contrary," Al-Delaimy said. "We need further studies to answer why they cannot quit. One hypothesis is that smokers are receiving an increase in nicotine dose by using e-cigarettes."
The scientists said that although e-cigarettes do not contain tobacco, users exhale a mixture of volatile organic compounds, heavy metals and ultra-fine particles that usually contain aerosolized nicotine in a cloud of vapor.
The findings show that daily smokers and women were more likely to have tried e-cigarettes.
Al-Delaimy said the study could inform the U.S. Food and Drug Administration and other regulators on the profile of e-cigarette usage among smokers as they create guidelines for the devices.
The county and city of San Diego last year approved restrictions on the sale and use of e-cigarettes last year, placing them in roughly the same category as traditional cigarettes.
The Veterans Affairs San Diego Healthcare System and San Diego State University also took part in the study, which was partially funded by the California Department of Public Health.