The effect of e-cigarette minimum legal purchase ages on cigarette use among pregnant teenagers

E-cigarettes were only introduced in the United States in 2007, but already several national data sources are reporting that e-cigarette use has surpassed cigarette use as the most commonly used tobacco product among adolescents. One policy effort to combat this trend is implementing minimum legal purchase ages (usually age 18) for e-cigarettes, similar to laws in place for cigarettes since 1988. New Jersey implemented the first e-cigarette minimum legal purchase age law in 2010, and as of November 2014, 40 states had such laws in place.

Two studies have treated e-cigarette minimum legal purchase ages as indirect price increases that may encourage substitution for cigarettes. These studies have found that these laws are associated with increases in cigarette use. Considering recent evidence that e-cigarettes are only 5% as harmful as regular cigarettes, this is likely a harmful pattern of substitution.

Cigarette use among pregnant women is especially harmful to the fetus. One of four rotating cigarette warning labels used in the United States warns: “Smoking by Pregnant Women May Result in Fetal Injury, Premature Birth, and Low Birth Weight.”

In this study, I explore the effect of e-cigarette minimum legal purchase age implementation on cigarette use among pregnant teenagers. Similar to the studies mentioned above, I hypothesize that e-cigarette minimum legal purchase ages impose an indirect cost on e-cigarette use, which causes substitution for more harmful cigarettes. I explore this hypothesis using national birth record data with geocode information provided by the National Cancer for Health Statistics for the years 2010 to 2014. I identify approximately 700,000 mothers that gave birth under the age of 18 from 31 states that use revised birth records, which provide trimester-specific average daily numbers of cigarettes smoked. I perform both a longitudinal analysis at the level of pregnancy-trimester, and a cross-sectional analysis at the level of pregnancy. In both the longitudinal and cross-sectional analyses, I find evidence that minimum legal purchase ages increase cigarette smoking on both the extensive and intensive margins of smoking. I also explore the effect of e-cigarette minimum legal purchase ages on low birth weight and premature birth using birth outcomes contained in the birth records. As a robustness check, I consider the possibility of non-parallel time trends influencing results. These results suggest a substitution relationship between cigarettes and ENDS, which raise concerns over the public health implications of current e-cigarette minimum legal purchase ages.