A preregistered experimental study tested the effects of message framing on breastfeeding and formula-feeding attitudes and intentions. It also examined whether affective reaction and information acceptance mediated these effects, and whether self-efficacy and perceived behavioral control (PBC) moderated them. Participants (282 pregnant women) were randomly assigned to a gain frame condition (benefits of breastfeeding), a loss frame condition (risks of not breastfeeding), or a control condition. Results showed two opposite indirect effects: the loss frame elicited negative affect, which lowered information acceptance; and conversely, the gain frame induced positive affect, thus increasing acceptance. These affective and cognitive responses differentially affected breastfeeding and formula-feeding attitudes and intentions, with the loss frame indirectly worsening the former (95% CI [-.24, -.08]) and improving the latter (95% CI [.03, .11]), while the gain frame worsened formula-feeding attitudes and intentions (95% CI [-.03, -.01]) and improved those related to breastfeeding (95% CI [.01, .08]). Additionally, low levels of breastfeeding self-efficacy and PBC amplified the negative effects of the loss-framed message and suppressed the positive effects of the gain-framed message. These findings highlight the affective and cognitive mechanisms through which risk-based language can have unintended, counterproductive effects. Breastfeeding promotion should emphasize benefits rather than risks and empower women's self-efficacy.