Endogenous opioid peptides in trichotillomania: An exploratory analysis of focused and automatic hair-pulling subtypes.

OBJECTIVE

Trichotillomania (TTM) is a body-focused repetitive behavior disorder characterized by recurrent hair pulling and functional impairment. Emerging evidence suggests that reward- and stress-related neurobiological mechanisms may contribute to its pathophysiology. This study investigated peripheral endogenous opioid peptide levels in TTM and examined differences across hair-pulling subtypes.

METHODS

This cross-sectional, case-control study included 45 adults with DSM-5-diagnosed TTM and 45 age- and sex-matched healthy controls. TTM subtypes (focused vs. automatic) were determined through primarily clinical interviews, supported by the Milwaukee Inventory for Subtypes of Trichotillomania-Adult Version (MIST-A; focused n = 27, automatic n = 18). Plasma β-endorphin and met-enkephalin levels were measured by ELISA. Clinical severity was assessed using standardized scales.

RESULTS

β-endorphin and met-enkephalin levels were significantly lower in the TTM group compared to healthy controls even after adjusting for depressive and anxiety symptoms. (both p < 0.001). β-Endorphin levels differed across TTM subtypes, with the lowest levels observed in the focused subtype. Focused hair-pulling severity was negatively correlated with β-endorphin levels, whereas automatic hair-pulling severity showed a positive correlation. Exploratory ROC analyses suggested both peptides may have preliminary discriminative value.

CONCLUSION

These findings provide the first evidence of reduced peripheral endogenous opioid levels in TTM and suggest subtype-specific differences in opioid system functioning. Alterations in endogenous opioids may be associated with reward- and stress-related mechanisms underlying hair-pulling behavior, particularly in the focused subtype. Further longitudinal and multimodal studies are warranted to clarify the role of opioid signaling in TTM.