Background and aim: Research examining the effects of oxytocin (OT) on psychiatric, social cognitive, and social behavioral outcomes regularly collect peripheral levels of OT as markers of central bioavailability. Such inferences rest on the assumption that central and peripheral levels of OT are directly associated. However, conflicting evidence from simultaneous sampling of central and peripheral OT questions the validity of this assumption. The aim of this meta-analysis was to evaluate the association between central and peripheral OT, as well as to account for heterogeneity in the literature by examining potential moderators of the association. Methods: Studies that report simultaneous sampling of central and peripheral OT in humans and other mammals were identified through a systematic search in the Embase database and through examination of reference lists and citation lists of retrieved articles. Data on effect sizes, sample sizes, subjects, and methods were extracted from eligible studies, and statistically synthesized in a random-effects meta-analysis. The impact of the moderator variables (experimental paradigm, species, central sampling location, biochemial analysis method, and peptide extraction procedure) on heterogeneity was examined in categorical moderator analyses. Results: 14 eligible studies with a total n=471 were retrieved in the systematic search. Overall, there was a positive association between central and peripheral concentrations of OT [r=0.28, p<0.0010], but a high level of heterogeneity [I2=68.82%, p<0.0001]. This heterogeneity was accounted for by experimental paradigm diversity [Qb=25.26, p<0.0001]. In a baseline condition, there was no evidence for association between central and peripheral OT concentrations [r=0.01, 95% CI (-0.15, 0.18)]. In contrast, there was a positive association after intranasal administration of OT [r=0.67, p<0.0001], and after experimentally induced stress [r=0.53, p<0.0001]. Discussion: The current meta-analysis does not support an association between central and peripheral concentrations of OT in a baseline condition. In research examining the psychiatric and social cognitive effects of the neuropeptide, peripheral OT in baseline conditions has been widely used as a proxy for central concentrations, but this approach may be inherently flawed. Furthermore, this meta-analysis may indicate a coordination of hypothalamic OT release into blood and the central nervous system after intranasal OT and after stress.