For those of you wondering about night or morning, especially with reta, here is the conclusion of my research.
1. IGF-1 output tracks GH pulse amplitude, and meal-induced insulin blunts that pulse at the pituitary — so protecting the fasted state outranks protecting circadian timing.
2. IGF-1 is timing-insensitive anyway (long half-life, integrates GH exposure across the day, builds to steady state over ~2 weeks), so the “lost nocturnal synergy” of a morning shot carries essentially no cost. That’s what makes the trade clearly favor morning fasted rather than being a close call.
3. The one boundary condition: if you could get a clean fasted window at night, night might edge ahead via synergy — so “morning wins” is conditional on the night option being under-fasted, not an absolute.
4. Retatrutide doesn’t flip this. Slowed gastric emptying mildly reinforces morning-fasted as the cleanest window, and improved insulin sensitivity helps the pulse. The variable it introduces — deficit-driven hepatic GH resistance lowering IGF-1 — is independent of injection timing, so it doesn’t change the timing conclusion.
The caveat - Important one IMO
1. GHRH-receptor signaling directly promotes slow-wave sleep via the preoptic/anterior hypothalamus, independent of GH release.
2. That effect is time-locked — it needs the agonist centrally active around sleep, which a short-half-life peptide only achieves with an evening dose.
3. It’s GHRH-receptor-specific, not a GH/IGF-1 effect (the GHRP-2 dissociation), so the mechanism is consistent rather than just “more GH → better sleep.”