Introduction Modified risk tobacco product (MRTP) claims for heated tobacco products (HTPs) that convey reduced exposure compared with conventional cigarettes may promote product initiation and transition among young people. We assessed the effects of a hypothetical MRTP claim for HTPs on young adults’ intention and perceptions of using HTPs and whether these effects differed by their current cigarette and e-cigarette use.

Methods We embedded a randomised between-subjects experiment into a web-based survey administered among a cohort of 2354 Southern California young adults (aged 20–23) in 2020. Participants viewed depictions of HTPs with an MRTP claim (n=1190) or no claim (n=1164). HTP use intention and HTP-related harm and use perceptions relative to cigarettes and e-cigarettes were assessed.

Results Overall, participants who viewed versus did not view the claim did not differ in HTP use intention (28.5% vs 28.7%) but were more likely to perceive HTPs as less harmful than cigarettes (11.4% vs 7.0%; p<0.001). The experimental effect on HTP use intention did not differ among past 30-day cigarette smokers versus non-smokers (interaction adjusted OR (AOR)=0.78, 95% CI 0.36 to 1.76) but differed among past 30-day e-cigarette users versus non-users (interaction AOR=1.67, 95% CI 1.02 to 2.68).

Discussion The hypothetical MRTP claim may lower young adults’ HTP harm perceptions compared with cigarettes but may not change HTP use intention overall or differentially for cigarette smokers. The larger effect on HTP use intention among e-cigarette users than non-users raises the question of whether MRTP claims may promote HTP use or HTP and e-cigarette dual use among young e-cigarette users.