Annual Research Review: Sex differences in conduct disorder – revisiting existing evidence and exploring future directions

Conduct disorder (CD) is a common psychiatric disorder in youth, characterized by severe and recurrent aggressive and antisocial behaviors and associated with substantial healthcare and societal costs. Rates of CD increase during adolescence in both sexes, with the male-to-female ratio narrowing to approximately 1:1. Although earlier work suggested potentially distinct pathways to CD in girls versus boys, few studies were adequately designed to investigate sex differences, limiting generalizability of existing findings from predominantly male samples to girls. Recent large-scale projects, such as the European multisite FemNAT-CD study, have addressed these limitations by oversampling girls and explicitly examining sex-specific characteristics. However, a systematic integration of these findings is lacking. This review therefore aims to synthesize current evidence on sex differences in CD across four core domains: clinical phenotype, risk factors, neurobiology, and treatment. It integrates key findings from FemNAT-CD alongside other relevant literature, with particular emphasis on implications for theories of (female) CD. Overall, girls and boys with CD appear far more similar than different. Youth with CD of both sexes differ markedly from their typically developing peers in comparable ways, particularly in neurobiological characteristics (e.g. emotion functioning, brain structural changes, neuroendocrine stress responses). Differences between girls and boys with CD are most evident in the clinical phenotype, including age-of-onset, callous-unemotional traits/limited prosocial emotions, aggression subtypes, and cooccurring psychiatric disorders. Overall, sex differences in CD are subtle and difficult to detect. Remaining limitations of the current evidence base and ways to enhance the clinical relevance of research in this field are discussed.