A new study published in Psychology & Neuroscience suggests that hormone levels in the body may be connected to psychopathic personality traits, particularly during adolescence and early adulthood. The research team conducted a systematic review and meta-analysis of studies examining endocrine system hormones like cortisol, testosterone, and oxytocin, uncovering a number of small but statistically significant associations. The strongest finding was a positive relationship between psychopathy and baseline cortisol levels.
Psychopathy is a personality construct associated with traits like emotional coldness, lack of empathy or guilt, impulsive behavior, and manipulativeness. Psychopathic traits can emerge early in life and, in some individuals, become more pronounced over time. These traits are typically divided into two dimensions. The first dimension relates to interpersonal and emotional features such as charm, callousness, and a lack of remorse. The second includes more behavioral elements like impulsivity and antisocial tendencies.
Researchers have long debated the biological basis of psychopathy. One theory, called the Low-Fear Hypothesis, suggests that people with psychopathic traits are less responsive to fear and stress, which might explain their inability to conform to social rules or respond emotionally to the suffering of others. This has led scientists to look at the body’s stress response systems—including hormone regulation—as a possible source of insight.
The new study aimed to bring clarity to the growing but inconsistent literature on this topic. Led by researchers from Portugal, the team reviewed 26 empirical studies published between 1998 and 2023. These studies explored how psychopathy might be related to specific hormones produced by the endocrine system, including cortisol (a hormone involved in stress), testosterone (related to aggression and dominance), dehydroepiandrosterone or DHEA (another stress-related hormone), estradiol (a form of estrogen), and oxytocin (which affects social bonding and empathy).
The researchers also performed a meta-analysis, which allows scientists to combine statistical results across multiple studies to get a more reliable estimate of an overall effect. They focused this analysis specifically on the relationship between basal (or resting) cortisol levels and psychopathy. Seven studies provided enough data to be included in this part of the research.
The meta-analysis found a statistically significant relationship between overall psychopathy and higher basal cortisol levels. A closer look at the different dimensions of psychopathy showed that this association was driven primarily by the second dimension—the one related to impulsive and antisocial behavior. No significant relationship was found between baseline cortisol and the first dimension of psychopathy, which involves emotional detachment and callousness.
These findings are notable because they partially contradict expectations from previous theories. Under the Low-Fear Hypothesis, one might expect individuals with psychopathic traits to show lower cortisol levels in general, reflecting a weaker stress response. Yet, this review found the opposite in many cases. People with higher psychopathy scores—particularly in the behavioral domain—tended to have higher resting cortisol levels.
Still, the results were far from uniform across studies. Some papers reported lower cortisol levels in individuals with high psychopathy or callous-unemotional traits, especially in young males. Others found no significant associations at all. Some studies observed differences in cortisol reactivity—how cortisol levels change in response to stress—rather than in resting levels. For example, in one study, individuals with psychopathic traits showed smaller changes in cortisol levels when exposed to a stressor.
In addition to cortisol, the researchers examined evidence linking psychopathy to other hormones. Several studies suggested that testosterone may be positively related to psychopathic traits, especially the behavioral dimension. For instance, higher testosterone levels were linked to increased impulsivity, aggression, and a reduced sensitivity to social punishment. However, not all studies supported this connection, and some found no meaningful relationship between testosterone and psychopathy at all.
The review also found mixed evidence regarding DHEA, a hormone that is often produced in response to stress. In some studies, higher DHEA levels were associated with more pronounced psychopathic traits, especially in adolescents. Other studies, however, found no such relationship. Similar inconsistency was seen in studies examining estradiol and oxytocin. Oxytocin, which plays a role in empathy and social bonding, was often lower in people with high levels of callous-unemotional traits, but again, not consistently across all studies.
The authors noted that differences in sample characteristics may have contributed to the variability in findings. Many studies were conducted in forensic settings using male participants, while others used community samples that included women. Psychopathy was measured in a variety of ways, including self-report questionnaires and clinician-administered interviews, which can yield different results. Hormone levels were also assessed using different protocols, and the timing of hormone collection can significantly influence the results—particularly for cortisol, which fluctuates throughout the day.
Given these inconsistencies, the researchers emphasized the importance of considering a range of contextual and biological factors in future work. These include age, sex, pubertal status, and co-occurring behavioral problems like conduct disorder. They also pointed out the need for more research into hormones that were underrepresented in the current review, such as adrenaline and noradrenaline. These hormones play important roles in the body’s acute stress response but were excluded from the analysis due to poor study quality.
Another limitation is that only seven of the 26 studies were suitable for inclusion in the meta-analysis. This small number limited the researchers’ ability to test whether factors like age or sex might change the strength of the relationship between cortisol and psychopathy. It also made it difficult to assess publication bias and study heterogeneity, which can influence the reliability of a meta-analysis.
Despite these limitations, the study offers an important step toward understanding psychopathy through the lens of neuroendocrinology. By identifying hormonal signatures that may be linked to specific dimensions of psychopathy, researchers hope to improve early detection and intervention efforts—particularly for adolescents who may be at risk of developing more severe forms of the disorder later in life.
The findings also raise broader questions about the role of biology in shaping personality and behavior. While hormones alone cannot explain psychopathy, they may interact with social and psychological factors in complex ways. Integrating hormonal data into existing psychological theories of psychopathy could offer a more complete picture of how these traits develop and persist over time.
In the long term, this line of research could inform more personalized treatment approaches. If certain hormonal patterns are found to be consistently associated with specific psychopathic traits, clinicians might one day be able to use hormone testing to support diagnosis, monitor treatment progress, or even develop biologically informed interventions. However, the study’s authors caution that such applications remain speculative for now and must be grounded in rigorous, future research.
The study, “Psychopathy and Hormonal Biomarkers: A Systematic Review and Meta-Analysis,” was authored by Catarina Braz Ferreira, Patrícia Figueiredo, Eduarda Ramião, Sofia Silva, and Ricardo Barroso.
