cigarettes (e-cigarettes) while tobacco companies reintroduced heated tobacco products (HTPs). The most notable brand of the latter being Philip Morris International's IQOS. While many countries do not allow alternative nicotine products to be marketed as less harmful than cigarettes, there are often subtle ABSTRACT INTRODUCTION Tobacco companies have introduced heated tobacco products (HTPs), such as IQOS, which may compete with e-cigarettes among smokers interested in switching to potentially reduced-risk products. Non-smokers may also start using IQOS if they believe this product is less harmful than other nicotine products. Smokers' and non-smokers' decisions may be driven by relative harm perceptions of emerging nicotine products. We aimed to examine relative harm perceptions between IQOS, e-cigarettes, and cigarettes, among nicotine product users and non-users. METHODS We conducted a web survey with Canadian respondents (aged ≥20 years; n=268) in September-October 2018. Perceptions about relative harm between IQOS (available for sale since 2017 and subject to the same comprehensive marketing restrictions as cigarettes in Canada), e-cigarettes, and cigarettes, were assessed among non-users (n=79), exclusive smokers (n=78), exclusive e-cigarette users (n=32), and dual users (n=79). Multiple logistic regression explored the association between relative harm perceptions and nicotine-use status, adjusting for sociodemographic variables. RESULTS Over half of respondents perceived IQOS as equally or more harmful than e-cigarettes (53.7%), while almost a quarter either reported IQOS as less harmful than e-cigarettes or were uncertain (22.7% and 23.5%, respectively). Two-thirds of respondents (65.7%) perceived e-cigarettes as less harmful than cigarettes, yet only half (48.1%) perceived IQOS as less harmful than cigarettes. Both exclusive and dual e-cigarette users, but not exclusive smokers, had higher odds of perceiving IQOS as more harmful than e-cigarettes and less harmful than cigarettes compared to non-users. CONCLUSIONS Most nicotine users and non-users perceive differential health risk across IQOS, e-cigarettes, and cigarettes. Although e-cigarettes are generally viewed as less harmful than cigarettes, the perceived harm of IQOS was unclear.