Message fatigue is a state in which people believe they have received too many similar messages conveying redundant information and feel a sense of exhaustion and boredom with those messages. A growing body of work suggests message fatigue inhibits persuasion, and a meta-analytic review can help to evaluate the strength and direction of the relationship between message fatigue and persuasive outcomes, explore potential moderators of that relationship, and shed light on productive paths forward. Our results indicated that, on average, increased message fatigue is associated with unintended outcomes such as increased endorsement of message-inconsistent beliefs and reduced intention to enact healthy behaviors ( r = −.25, k = 18, N = 24,236). Substantial heterogeneity was observed and, in general, left unexplained by our coded moderators. We speculate about the drivers of the observed heterogeneity and reflect on paths forward in this area of research.