We explore how conspiracy beliefs change the effectiveness of gain- vs. loss-framed messages in promoting health-protective behavior. We focused on various recommended COVID-19 protective measures, not only vaccinations but also other preventive (like wearing masks) and detection behaviors (like testing). Our results indicate that conspiracy beliefs moderate the effectiveness of gain vs. loss framing. When participants endorse conspiracy worldviews above the average level, the gain frame may be more effective than the loss frame. In other words, in the loss frame condition, conspiracy beliefs negatively and significantly predicted attitudes toward the behavior recommended. However, in the case of the gain frame, the relationship between conspiracist views and attitudes toward promoted behavior was weaker or even nonsignificant. We also found, although only in the case of one behavior, that when participants' eagerness to look for conspiracies almost does not exist, the loss frame may be a better option than the gain frame. Finally, neither of these effects was mediated by emotional reactance or anxiety.