SignificanceCigars are sometimes marketed with cannabis references because they are often used for smoking blunts (a cigar with cannabis). However, little research exists on the impact of cannabis co-marketing on cigar perceptions. MethodsParticipants included 506 US youth (ages 15–20) recruited April-June 2023 through Qualtrics who reported ever using little cigars or cigarillos (LCCs), past 30-day use of LCCs, or susceptibility to using LCCs. We then conducted a between-subjects experiment, randomizing youth to view one of two cigarillo packages: 1) a package with cannabis co-marketing (i.e., the package included a cannabis-related flavor descriptor and the word “blunt” appeared in the brand name and product label) or 2) a package with no cannabis co-marketing. We assessed the effects of the packaging on perceptions of product ingredients, addictiveness and harm perceptions, product appeal, susceptibility to using the product shown, and purchase intentions. ResultsPackages with cannabis co-marketing were perceived as more likely to contain cannabis (OR: 5.56, 95 % CI: 3.73, 8.27) and less likely to contain tobacco (OR: 0.42, 95 % CI: 0.25, 0.70) or nicotine (OR: 0.57, 95 % CI: 0.40, 0.82). Cannabis co-marketing also led to higher susceptibility to using the product shown (B: 0.21, p = 0.02). We did not find evidence that cannabis co-marketing changed harm perceptions or purchase intentions. ConclusionsAmong a sample of US youth, cannabis co-marketing on cigar packages may change perceptions of product ingredients and increase susceptibility to using such products, which could lead to the initiation of cigars and cannabis.