Relationship Between Second-to-Fourth Digit Ratio (as a Biomarker) and Tramadol Dependence

Abstract

Objectives: Digit ratio (2D:4D ratio), the ratio between the length of the second and fourth fingers, is considered a putative biomarker of prenatal testosterone exposure relative to estrogen exposure, consequently it has been linked to several behaviors within the personality such as academic performance, nicotine and alcohol misuse, and also with other behaviors. Our aim is to investigate any possible association between 2D:4D ratios and tramadol dependence. Participants and Methods: A group of 99 male patients with tramadol dependence [diagnosed by Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV)] were interviewed and their digital ratios were (2D:4D ratios) measured, then the findings were compared with 99 healthy males. Results: Patients with tramadol dependence had lower 2D:4D ratios of their right and left hands when compared with those without tramadol use disorder. There was no significant correlation between 2D:4D ratio and age of patients, age of onset, duration, and amount of tramadol use. Conclusion: These findings suggest that high prenatal exposure to testosterone levels could be associated with tramadol dependence as detected by a lower 2D:4D ratio.