This is because they are allergic to something
You may notice the effects of short-acting peptides within a few weeks, or in some cases within the first few days
If you want the appetite and cravings side of this story, how stress drives sugar cravings and reward eating, we cover that separately in Cortisol, Cravings, and GLP-1
BPC-157, by contrast, modulates growth factor pathways (VEGF, FGF, NO system) involved in tissue repair without directly activating hormone receptors (Sikiric et al., J Physiol Pharmacol 2018)
Ideally, quantification of secreted GLP-1 must be based on its concentration immediately at the site of its release in the intestine where it exerts a local effect to activate vagal sensory neurons within the intestinal wall so that vasovagal reflexes important to global metabolic homeostasis can be initiated 26,27