People with pronounced primary psychopathic traits have lower morning levels of cortisol — a key stress hormone — compared to others. This conclusion was reached by researchers who studied university students in the United States. In the afternoon, however, this relationship disappears and does not depend on the participants’ sex. The study was published in the journal Social Neuroscience (SN).

Psychopathic traits include emotional coldness, lack of empathy, absence of guilt, and a tendency toward manipulation. In psychology, these traits are commonly divided into primary and secondary psychopathy. Primary psychopathy is associated with low anxiety, superficial charm, and a weak response to threats and is believed to be largely influenced by innate factors. Secondary psychopathy, by contrast, is characterized by impulsivity, emotional instability, and heightened stress reactivity and is more often linked to adverse life experiences.

The research team, led by Todd Armstrong, examined the relationship between psychopathic traits and the hormones cortisol and testosterone. The study involved 552 undergraduate students (average age 20), who completed psychological questionnaires and then provided saliva samples for hormone analysis.

Samples were collected from morning to evening, allowing the researchers to compare hormone levels at different times of day. In addition, participants completed a brief stress task — a two-minute speech about their strengths and weaknesses — after which hormone measurements were repeated.

The results showed that lower baseline cortisol levels before the stress task were characteristic of individuals with pronounced primary psychopathy, but only in the morning hours. This association disappeared later in the day. The participants’ sex had no effect on the findings, and no relationship was found between cortisol levels and secondary psychopathy.

According to the authors, the data point to an important role of cortisol in the biological mechanisms underlying primary psychopathic traits.

“Although recent research has focused on the interaction between testosterone and cortisol, our results suggest that a direct link between cortisol and psychopathic traits may be key,” the researchers noted.