Background How electronic cigarettes and similar products (e-cigarettes) are defined affects how they are regulated, particularly whether existing laws for cigarettes apply, including sales and marketing, youth access, smoke-free and taxation laws.

Methods We examined the text of 46 bills that define e-cigarettes enacted in 40 states and characterised how e-cigarettes and similar products were defined.

Results States enact laws creating new product categories for e-cigarettes separate from the ‘tobacco product’ category (eg, ‘alternative nicotine product,’ ‘vapour product,’ ‘electronic nicotine device’), with four states explicitly excluding e-cigarettes from ‘tobacco products.’ Twenty-eight states do not include e-cigarettes in their definitions of ‘tobacco products’ or ‘smoking,’ eight include e-cigarettes as ‘tobacco products,’ three include e-cigarettes in ‘smoking.’ Sixteen states’ definitions of e-cigarettes require nicotine, and five states pre-empt more stringent local laws. Tobacco and e-cigarette industry representatives tried to shape laws that benefit their interests.

Conclusions Definitions separating e-cigarettes from other tobacco products are common. Similar to past ‘Trojan horse’ policies, e-cigarette policies that initially appear to restrict sales (eg, limit youth access) may actually undermine regulation if they establish local pre-emption or create definitions that divide e-cigarettes from other tobacco products. Comparable issues are raised by the European Union Tobacco Products Directive and e-cigarette regulations in other countries. Policymakers should carefully draft legislation with definitions of e-cigarettes that broadly define the products, do not require nicotine or tobacco, do not pre-empt stronger regulations and explicitly include e-cigarettes in smoke-free and taxation laws.