Category: receptor_pharmacology
Explains the most user-reported phenomenon of semaglutide/tirzepatide therapy: 'food noise' — the constant intrusive thinking about food — drops away within days to weeks of starting, separate from and earlier than the weight loss itself. GLP-1 receptor agonists (semaglutide, liraglutide, dulaglutide) and the dual GIP/GLP-1 agonist tirzepatide act through GLP-1R, a Gs-coupled GPCR (Drucker 2018 review). The peripheral effects — delayed gastric emptying (a key driver of early satiety + the sulfur-burp side effect from delayed protein digestion) and pancreatic β-cell glucose-dependent insulin secretion — are real, but the appetite-and-reward effects are CNS-mediated. Farr 2016 confirmed GLP-1R expression in the human hypothalamus, parietal cortex, and medulla; van Bloemendaal 2014 showed that GLP-1 receptor activation reduces fMRI signal in appetite- and reward-related brain regions (ventral striatum, insula, OFC, amygdala) in response to food cues. The phenomenology — 'I just don't think about food anymore' — maps cleanly onto this reward-cue dampening. Clinical magnitude: semaglutide 2.4 mg weekly produced a 14.9% body-weight reduction in STEP 1 (Wilding 2021); tirzepatide 15 mg weekly produced 20.9% in SURMOUNT-1 (Jastreboff 2022). GI side effects (nausea, sulfur burps from prolonged gastric retention, constipation, reflux) cluster early and usually attenuate over 8-12 weeks. Mechanism overlap with central reward explains the off-label observations of reduced alcohol craving and possibly other reward-driven behaviors (compulsive shopping, nail-biting) — an active research area.