IMPORTANCE Electronic cigarettes (e-cigarettes) are less harmful to users than combustible cigarettes. However, public health and media reporting have often overstated the potential risks of e-cigarettes, and inaccurate perceptions of the harms of vaping relative to smoking are pervasive.

OBJECTIVE To examine time trends in harm perceptions of e-cigarettes compared with combustible cigarettes among adults who smoke.

DESIGN, SETTING, AND PARTICIPANTS This nationally representative monthly cross-sectional survey study was conducted from November 2014 to June 2023 in England. Participants were adults who currently smoke.

MAIN OUTCOMES AND MEASURES Participants were asked whether they thought e-cigarettes were less harmful, equally harmful, or more harmful than cigarettes, or did not know, with the proportion responding less harmful (vs all other responses) as the primary outcome. Logistic regression was used to test associations between survey wave and participants' perceptions of the harms of e-cigarettes.

RESULTS Data were collected from 28 393 adults who smoke (mean [SD] age, 43.5 [17.3] years; 13 253 [46.7%] women). In November 2014, 44.4% (95% CI, 42.0%-46.8%) thought e-cigarettes were less harmful than cigarettes, 30.3% (95% CI, 28.2%-32.6%) thought e-cigarettes were equally harmful, 10.8% (95% CI, 9.4%-12.3%) thought they were more harmful, and 14.5% (95% CI, 12.9%-16.4%) did not know. However, by June 2023, the proportion who thought e-cigarettes were less harmful had decreased by 40% (prevalence ratio, 0.60; 95% CI, 0.55-0.66), and the proportion who thought e-cigarettes were more harmful had more than doubled (prevalence ratio, 2.16; 95% CI, 1.84-2.54). Changes over time were nonlinear: late 2019 saw a sharp decline in the proportion who thought e-cigarettes were less harmful and increases in the proportions who thought they were equally or more harmful. These changes were short-lived, returning to pre-2019 levels by the end of 2020. However, perceptions worsened again from 2021 up to the end of the study period: the proportion who thought e-cigarettes were more harmful increased to a new high, and the proportion who thought e-cigarettes were less harmful decreased to levels comparable to those in late 2019. As a result, in June 2023, the perception that e-cigarettes were equally as harmful as cigarettes was the most commonly held view among adults who smoke (33.7%; 95% CI, 31.4%-36.1%), with roughly similar proportions perceiving e-cigarettes to be less (26.7%; 95% CI, 24.6%-28.9%) and more (23.3%; 95% CI, 21.1%-25.7%) harmful.

CONCLUSIONS AND RELEVANCE This survey study of adults who smoke in England found that harm perceptions of e-cigarettes have worsened substantially over the last decade, such that most adults who smoked in 2023 believed e-cigarettes to be at least as harmful as cigarettes. The timing of the 2 most notable changes in harm perceptions coincided with the e-cigarette, or vaping product, use-associated lung injury outbreak in 2019 and the recent increase in youth vaping in England since 2021.