Retatrutide — 5mg

Retatrutide 5mg is the smallest-vial presentation of Eli Lilly's triple GLP-1/GIP/glucagon receptor agonist. The compound itself is identical across vial sizes — a 39-amino acid synthetic peptide with a C20 fatty diacid modification enabling albumin-mediated half-life extension and once-weekly subcutaneous dosing. What differs is the dose-finding precision the 5mg format enables.

Fine-grained titration is the core research use case for this vial size. The Phase 2 trial (NCT04881760) and Phase 3 TRIUMPH-4 (NCT05929066) both used 2mg / 4mg / 8mg / 12mg escalation schedules, with some Phase 3 arms adding a 6mg intermediate step to soften the GI side-effect ramp. The 5mg format supports research into even finer intermediate steps — 1mg microdose starts, 3mg transitional doses — which are relevant for subjects who exhibit exaggerated pharmacodynamic response to GLP-1 class drugs. It is also useful for late-phase dose-reduction research where subjects have reached maintenance and are being titrated down toward minimum effective doses.

All mechanistic data and clinical outcomes documented for the 8mg, 10mg, and 20mg formats apply here. Phase 3 TRIUMPH-4 reported 28.7% mean weight loss at 68 weeks, the strongest clinical weight reduction data in any obesity pharmacotherapy to date. The 5mg vial format is the most cost-efficient entry point for new research programs running conservative titration schedules where full 12mg exposure is not part of the protocol.