In the United States, individual states established a minimum legal sale age (MLSA) for e-cigarettes between 2010 and 2016 when a federal MLSA came into place. These policies provide a natural experiment from which we can better understand the effect that e-cigarettes have on youth combustible tobacco use. This paper uses National Youth Tobacco Survey data to estimate the effect of the gradual roll-out of e-cigarette MLSAs in the United States on youth e-cigarette use, cigarette use, and cigar use (i.e., cigars, cigarillos, or little cigars). Using an estimator designed to correct for dynamic heterogeneity in treatment effects, e-cigarette MLSAs are estimated to reduce lifetime e-cigarette use by approximately 25% and increase daily cigarette use and daily cigar use by approximately 35%. Therefore, these MLSAs operate as intended in reducing e-cigarette use, although at the expense of more dangerous combustible tobacco use. The Food and Drug Administration should consider the impact of e-cigarette availability in reducing youth combustible tobacco use as an important public health benefit of e-cigarettes in their regulatory activity.

在美国，2010 年至 2016 年联邦 MLSA 出台时，各个州都为电子烟设定了最低法定销售年龄 (MLSA)。这些政策提供了一个自然实验，我们可以从中更好地了解电子烟对青少年可燃烟草使用的影响。本文使用全国青年烟草调查数据来估计美国逐步推出电子烟 MLSA 对青年电子烟使用、香烟使用和雪茄使用（即雪茄、小雪茄或小雪茄）的影响). 使用旨在校正治疗效果的动态异质性的估计器，估计电子烟 MLSA 可将终生电子烟使用量减少约 25%，并使每日香烟使用量和每日雪茄使用量增加约 35%。所以，这些 MLSA 的运作旨在减少电子烟的使用，但以使用更危险的可燃烟草为代价。美国食品和药物管理局应在其监管活动中考虑电子烟供应对减少青少年可燃烟草使用的影响，将其作为电子烟的一项重要公共健康益处。