Many people remove the tobacco leaf from cigars and replace it with cannabis (ie, blunts), but few studies have examined whether messages about the risks of cigars, like warnings on cigar packages, can affect blunt use. Participants were 438 U.S. adults who reported past 30-day cigar use and ever blunt use, recruited from a probability-based national panel to take an online survey. In a 2 × 2 experiment with a between-subjects design, we manipulated two cigar warning characteristics: (1) warning type: text-only versus pictorial (ie, text + image) and (2) warning size: 30% (smaller) versus 50% (larger) of the product package. Participants then viewed six different warnings on a fictious cigarillo package, within their randomly assigned condition. After evaluating all stimuli, participants were asked the extent to which the warnings discouraged them from wanting to use cigars to smoke cannabis (ie, blunt perceived warning effectiveness). Response options ranged from "not at all" (1) to "a great deal" (5). We observed no main effects of warning type or size on blunt perceived warning effectiveness. However, a significant interaction existed between the two experimental manipulations (p = .009). Whereas adding images made no difference to blunt perceived warning effectiveness when warnings were smaller (simple effect: -0.22, p = .28), images mattered for larger warnings. Specifically, adding images increased blunt perceived warning effectiveness when warnings were 50% of the product package (simple effect: 0.52, p = .008). This experiment provides preliminary evidence that larger pictorial cigar warnings may discourage blunt use relative to larger but text-only warnings. Blunts, which are hollowed out cigars with tobacco leaf wrappers that are filled with cannabis leaf, are one of the most common ways in which tobacco and cannabis are used simultaneously, yet few studies have examined whether messages about the risks of cigars can affect blunt use. We conducted an online experiment concerning the perceived effectiveness of cigar warnings among people who use blunts recruited from a probability-based panel. Results provide novel, preliminary evidence that larger pictorial cigar warnings may discourage blunt use, relative to larger but text-only warnings. More research evaluating cigar warnings on blunt use is needed.