A meta-analysis of 89 effect sizes based on the responses of 19,930 participants was conducted to estimate the magnitude of the relationship between substance-related implicit cognitions and the use of legal and illegal substances. The analysis produced a weighted average effect size of r=.31. Moderation analyses revealed significant heterogeneity in effect sizes related to facet of implicit cognition, measurement strategy, sample composition, and substance type. The largest effect sizes were found in studies that assessed implicit semantic associations, employed word association measures, and focused on marijuana use. The findings suggest that implicit cognition is a reliable predictor of substance use, although effect sizes vary as a function of several methodological factors.