text: “endogenous opioid system”—involved in reward and the regu- 
  lation of pain and affect—have been documented (Bresin and 
  Gordon 2013), as low basal plasma levels of β-endorphins (which 
  are peripherally released following tissue damage) in psychiatric 
  patients (van der Venne et al. 2021, Cakin Memik et al. 2023). 
  Lower salivary levels of β-endorphins have also been registered 
  immediately before NSSI, compared to post-NSSI (Störkel et al. 
  2021). Thus, an imbalance in the opioid system might be a rel- 
  evant component in NSSI, where self-injures might be acted 
  to initiate the release of β-endorphins to restore homeostasis 
  (Stanley et al. 2010, Bresin and Gordon 2013). Another line 
  of research examined “nociceptive dysregulation,” with possible 
  hypoalgesia (Kirtley et al. 2016), showing higher pain thresh- 
  olds and lower pain intensity in adolescents with NSSI (Nock 
  et al. 2006, 2009, van der Venne et al. 2021). Recent works failed 
  to replicate these findings but reported specific alterations in 
  descending inhibitory pain control (Leone et al. 2021, Lalouni 
  et al. 2022). Despite some inconsistencies, this is an area that 
  is worth further investigation. It remains to investigate to what 
  extent the perspective on NSSI offered here could be extended to 
  cover the aforementioned body of evidence and whether active 
  inference could help integrate the different perspectives we have 
  discussed. 