What to Expect the First Week of Microdosing Retatrutide

Retatrutide is an investigational multi-agonist peptide, so information comes from early clinical trial data rather than real-world long-term use. In phase 2 studies such as those reported in the New England Journal of Medicine (2023) participants began with very low “microdose-style” doses (1–2 mg weekly) before gradually increasing. Even at these small starting doses, several early patterns showed up.

During the first week, most people noticed mild appetite changes. Instead of dramatic hunger suppression, participants typically reported feeling full sooner or thinking about food less often. Many described it as having a “quieter appetite.”

The most common early side effects were mild nausea, slower digestion, or early fullness, which is similar to what’s often seen with GLP-1 medications. A smaller number of participants also experienced fatigue, especially in the first few days when the body adjusts to new hormone signaling. These findings are reflected across early industry reports, including Eli Lilly’s Phase 2 trial data (2023).

The big effects that retatrutide is known for include major appetite suppression and significant weight reduction. These effects do not show up in the first week. They do build steadily over several weeks as the dose is increased,

Friendly reminder: This article is written in December 2025. Retatrutide is not yet FDA-approved. I am not a doctor or peptide expert. Anyone considering microdosing should do so only with medical supervision, especially given that long-term safety data are still limited.