The relationships among the Dark Triad (DT) traits—Machiavellianism, narcissism, and psychopathy—are well-established in psychological literature. However, with the inclusion of everyday sadism in the proposed Dark Tetrad, it is important to determine whether sadism adds significant explanatory power beyond psychopathy, especially given its high correlation. In this study, we examined whether sadism contributed unique variance over psychopathy in studies where both traits were assessed. A review of PubMed, Google Scholar, and ScienceDirect yielded 185 studies meeting our inclusion criteria, comprising 104,452 participants. We analyzed sample characteristics, including type, size, gender distribution, age, and key correlates such as narcissism, Machiavellianism, the Big Five, and Honesty-Humility. Our results indicate a substantial overlap between sadism and psychopathy, with both traits being strongly related to the other DT traits and showing no correlation with Openness. These findings highlight the need for future research to account for this overlap when interpreting the relationships between sadism, psychopathy, and related psychological constructs.