Opioid peptides as stress hormones. Stress triggers a release of proenkephalin that gets processed into enkelytin and Met-enkephalin. This step characterizes opioid peptides as stress hormones at the border to stress autoregulation, i.e., endogenous stress reduction, since they have the functions of a 'double-edged sword': in part, the opioid peptides/endorphins enable the stressed organism to stay active beyond the normal or physiological duration of a stress cycle (e.g., ca. 90 minutes max. in humans), by signalling the individual to keep up with the stress activity (because it might be biologically necessary), while reducing pain and other physiological companions of a prolonged stress response. In this case, the activated immune response and defence is upheld, typical signs of stress response activity prevail. However, the opioid peptides already prepare for the relaxing and recovering part of stress, i.e., stress management, since motivation and behavioral adjustments are positively influenced; references: [Fricchione & Stefano, 1994; Stefano & Scharrer, 1994; Stefano & Kream, 2008a; Stefano et al. 1996b; Stefano et al. 1998a; Stefano et al. 2001a; Stefano et al. 2005a; Stefano et al. 2005d].