An international team of scientists from Canada, Iran, Switzerland and the United Kingdom identified a link between the 2D:4D finger length ratio and symptoms associated with several psychopathological personality traits, including antisocial behavior and substance use. The findings were published in the journal of scientific record Journal of Psychiatric Research (JPR).
Previous studies have shown that the 2D:4D ratio, which compares the length of the index finger (2D) to the ring finger (4D), may reflect early hormonal influences in the womb. A higher prenatal testosterone relative to estrogen typically results in a lower 2D:4D ratio, often producing a relatively longer ring finger compared with the index finger.
The goal of the current work was to deepen understanding of how finger length ratios relate to certain mental health conditions and personality characteristics. The focus was on individuals with amphetamine dependence (AUD), antisocial personality disorder (ASPD), and a combination of both diagnoses (AUD + ASPD).
A total of 80 participants were recruited and divided into two main groups: 44 with a clinical diagnosis (25 with AUD, 10 with ASPD, and nine with AUD+ASPD) and 36 healthy controls. Participants completed a series of assessments designed to measure personality traits and overall mental state.
Results showed that the clinical group tended to have a significantly lower 2D:4D ratio than the healthy control group, indicating a relatively longer ring finger compared with the index finger among those with AUD, ASPD, and particularly AUD+ASPD. Within the sample, men generally exhibited a lower 2D:4D ratio than women.
The researchers noted a clear association between higher levels of psychopathology and lower 2D:4D ratios, suggesting greater prenatal exposure to testosterone and lower exposure to estrogen among individuals with more pronounced psychiatric symptoms. This does not predict future outcomes but signals a tendency toward certain behavioral patterns in line with prenatal hormonal exposure. In examples from other populations, such as Swedish Olympic athletes, a lower 2D:4D ratio has been observed among many women, reflecting higher prenatal testosterone levels in those cases as well. (Source: Journal of Psychiatric Research)
Overall, the findings contribute to a growing body of evidence about how early biological factors may relate to later behavioral and personality profiles. They are a reminder that while finger length ratios can be associated with certain tendencies, they do not determine individual destinies or necessarily coincide with antisocial behavior or drug use in any given person. Further research in diverse groups and settings will help clarify the strength and limitations of these associations and how they fit into broader models of mental health risk and resilience.