Background: Health warning labels (HWLs) are evidence-based tobacco control strategies; however, their application to e-cigarettes and related impacts (e.g. on perceived risk), including across countries with different regulations, are understudied. Design and Methods: Using 2021 survey data from 927 US and Israeli adults reporting past-month tobacco use, multivariate analyses examined: (1) sociodemographics in relation to self-reported impact of e-cigarette HWLs (i.e. more concerned about e-cigarette use, reassured, no effect) among those who noticed e-cigarette HWLs (multinomial regressions); and (2) HWL impacts in relation to use intentions and perceived addictiveness and harm (linear regressions). Results: Among those who noticed HWLs ( n = 835, 90.1%), 34.1% reported HWLs resulted in greater concern about e-cigarette use, 45.5% no effect, and 20.4% reassurance. Factors associated with greater concern (vs no effect) included e-cigarette non-use (vs use; aOR = 1.69, 95% CI:1.22, 2.38), US (vs Israel) resident (aOR = 1.65, 95% CI:1.16, 2.34), age 18–25 (vs 36–45; aOR = 1.72, 95% CI:1.11, 2.67), and more education (aOR = 1.85, 95% CI:1.30, 2.63). Factors associated with being reassured (vs no effect) included use of cigarettes (aOR = 1.71, 95% CI:1.06, 2.75), e-cigarettes (aOR = 2.64, 95% CI:1.77, 3.94), and other tobacco (aOR = 2.11, 95% CI:1.39, 3.21), and Israeli resident (aOR = 2.33, 95% CI:1.47, 3.70). Not noticing HWLs (vs no effect) correlated with lower intentions (β = −0.44, 95% CI:−0.87, −0.01), perceived addictiveness (β = −0.61, 95% CI:−1.05, −0.18), and harm (β = −0.56, 95% CI:−0.95, −0.18); reassurance correlated with greater use intentions (β = 0.48, 95% CI:0.12, 0.83); and greater concern was unassociated with use intentions or perceived risk. Conclusion: Effects of differing e-cigarette HWLs in distinct subpopulations warrant research. Despite being noticed, they may have no effect or encourage e-cigarette use.