Opioid system regulates endometrial function, influencing **endometriosis**-associated subfertility beyond pain

Endometriosis, a chronic inflammatory disease affecting 10-15% of reproductive-age women, is a leading cause of female subfertility. Current management, primarily surgical excision and hormonal suppression, often fails to address underlying reproductive dysfunction or is incompatible with pregnancy. While the opioid system has traditionally been studied for pain management in endometriosis, this review explores its less-understood roles in endometrial function and reproductive health, highlighting a critical gap in understanding its non-analgesic contributions to disease pathogenesis.

This comprehensive review synthesized existing literature on the opioid system's role in endometrial function and reproductive health, moving beyond its traditional focus on pain management. Researchers systematically discussed the presence and cyclical fluctuations of opioid receptors and peptides within the uterine environment. The methodology involved integrating classical opioid research with modern challenges in endometriosis-associated infertility to identify critical knowledge gaps and potential non-hormonal therapeutic targets.

The review found that opioid receptors and peptides are present and exhibit cyclical fluctuations within the uterine environment, actively influencing key processes often dysregulated in endometriosis. These include tissue remodeling, angiogenesis, and apoptosis.

The synthesis of evidence suggests the opioid system is an active participant in the pathogenesis of endometriosis-associated infertility, rather than merely a bystander in pain signaling. This perspective highlights non-analgesic opioid pathways as crucial for endometrial function and reproductive outcomes, identifying a significant shift from the traditional pain-centric view. The authors emphasize that these pathways may contribute directly to the disease's reproductive dysfunction, offering new avenues for intervention.