Background IQOS was the first heated tobacco product to receive Food and Drug Administration (FDA) authorisation for ‘reduced exposure’ marketing claims, which has been exploited globally.

Methods In November–December 2021, we conducted a survey-based 3×3 factorial experiment among US (n=1128) and Israeli adults (n=1094). We presented: (1) reduced exposure, reduced risk and control messaging and (2) 2 variations of FDA endorsement and control messaging. Each participant was randomly assigned to evaluate 2 ads (displayed on different ad imagery), then completed assessments of perceived relative harm, exposure and disease risk and likelihood of personally trying or suggesting IQOS to smokers. Ordinal logistic regression examined messaging conditions and their interactions, on the 5 outcomes, respectively, adjusting for covariates.

Results Control (vs reduced exposure) messaging resulted in higher perceived relative harm (adjusted OR (aOR)=1.29, 95% CI=1.12 to 1.48), exposure (aOR=1.34, 95% CI=1.17 to 1.54) and disease risk (aOR=1.23; 95% CI=1.08 to 1.40), and lower likelihood of suggesting IQOS to smokers (aOR=0.85; 95% CI=0.74 to 0.97). Reduced risk (vs exposure) messaging resulted in lower perceived relative harm (aOR=0.86; 95% CI=0.75 to 0.99). One FDA endorsement message (‘IQOS (completed) the US FDA examination of tobacco products. FDA concluded that IQOS is a better choice for adult smokers’) was associated with greater likelihood of suggesting IQOS to smokers, relative to control (aOR=1.19; 95% CI=1.04 to 1.37). No interactions between risk/exposure messaging and FDA endorsement messaging were found. Additionally, Israeli participants, cigarette users and men perceived lower relative harm and exposure and greater likelihood of trying or suggesting IQOS to smokers.

Conclusions Regulators must monitor direct and indirect advertising content of modified risk tobacco product-authorised products and prevent potentially harmful misinterpretations.