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

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.

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.

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.

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.