Objectives Many parents recall hearing of human papillomavirus (HPV) vaccine through drug company advertisements. This study sought to examine whether parents accurately recall the source (ie, sponsor) of advertisements promoting HPV vaccine and the impact of drug company advertisements.

Methods A US national sample of 544 parents of adolescent boys aged 11–17 participated in an online between-subjects experiment. Parents viewed an advertisement encouraging HPV vaccination for boys with a logo from a randomly assigned source. Parents rated trust, likability and motivation for vaccination while viewing the advertisement and later indicated who they believed sponsored it.

Results Nearly half (43%) of parents who viewed a hypothetical advertisement containing a logo incorrectly identified the advertisement source. More parents correctly identified the source of drug company advertisements than advertisement from other sources (62% vs 25%, OR 4.93, 95% CI 3.26 to 7.46). The majority of parents who saw a logo-free advertisement believed a drug company created it (60%). Among parents who correctly identified the advertisement source, drug company advertisements decreased motivation to vaccinate their sons, an association mediated by reduced liking of and trust in the advertisements.

Conclusions Parents were more accurate in identifying drug company advertisements, primarily because they tended to assume any advertisement was from a drug company. Public health organisations may need to take special measures to ensure their messages are not perceived as sponsored by drug companies.