The escalation schedule
The retatrutide dosage chart documents the Phase 2/3 weekly escalation schedule that Eli Lilly carried into the TRIUMPH registrational program: 2 mg for weeks 1–4, 4 mg for weeks 5–8, 8 mg for weeks 9–12, and 12 mg from week 13 onward as the maintenance / Phase 3 primary dose. The calculator takes a target week as input and returns the corresponding weekly milligram dose plus the purpose of that step (initiation, escalation, mid-range therapeutic, maintenance). It does not return a personalized recommendation; it surfaces the trial schedule.
Retatrutide is investigational. As of April 2026 it has no FDA approval, no marketing authorization in any jurisdiction, and no branded pen presentations. Lilly's NDA filing is expected Q4 2026–Q1 2027, with a PDUFA target window in mid-to-late 2027. The chart therefore omits pen concentrations entirely; it documents the escalation pattern that has been studied, not a product you can fill at a pharmacy.
The 4-week step cadence matches the typical incretin titration rhythm: long enough for receptor adaptation and GI tolerance to accommodate the next step, short enough to reach maintenance inside a quarter.
Why those specific doses
Retatrutide (LY3437943) co-activates three receptors: glucose-dependent insulinotropic polypeptide (GIP), GLP-1, and glucagon. The first two are now familiar from semaglutide and tirzepatide. The third, glucagon agonism, is what makes retatrutide structurally different: glucagon receptor activation drives hepatic fat oxidation and increases resting energy expenditure, layering an energy-output effect on top of the appetite-and-emptying pathway that GLP-1 supplies.
The 12 mg weekly dose was selected from the Phase 2 dose-finding program. In the Phase 2 type 2 diabetes trial (Rosenstock et al., 2023, Lancet, PMID 37385280), 12 mg (with 2 mg start, escalating in 4-week steps) produced an HbA1c reduction of −2.02% at 24 weeks and −16.94% body weight at 36 weeks, both the largest effects in the trial. The TRIUMPH Phase 3 design paper (Giblin et al., 2026, Diabetes Obes Metab, PMID 41090431) carried 12 mg forward as the primary maintenance dose across the four-trial obesity / OSA / OA / CV basket. TRIUMPH-4 (knee osteoarthritis, N=445, 68 weeks) reported the now-quoted 28.7% mean weight loss at the 12 mg maintenance dose.
The 2 mg start, rather than 4 mg, materially reduces GI adverse-event frequency during titration without sacrificing the eventual maintenance effect.
Assumptions and limits
The calculator assumes weekly subcutaneous administration. Retatrutide's fatty-diacid conjugation gives it an approximately 6-day plasma half-life, which is what supports once-weekly dosing. That is the only schedule the trial program has tested.
Investigational status is the largest single caveat. Phase 3 results to date (TRIUMPH-4 knee OA, TRANSCEND-T2D-1) have confirmed Phase 2 efficacy directionally, but the broader TRIUMPH obesity, OSA, and cardiovascular outcomes trials are still running. Final labeling (including approved dose range, indications, and contraindications) does not yet exist.
A specific safety signal worth flagging: TRIUMPH-4 reported dysesthesia (abnormal skin sensations) in 20.9% of patients at the 12 mg dose. TRANSCEND-T2D-1 reported it at 2.3–4.5%. The gap between trials may reflect population differences or ascertainment, but at face value roughly one in five patients at maintenance dose in TRIUMPH-4 reported it. Class-typical GI adverse events (nausea, vomiting, diarrhea, constipation) and a modest heart-rate elevation are also documented and concentrate during escalation.
The gray-market reality is the second large caveat. Pre-approval, retatrutide circulates through research-chemical vendors with research-only labeling and no quality assurance; no batch certificates of analysis, no HPLC purity reporting, no endotoxin testing, no Lilly chain of custody. This calculator does not endorse that channel. The schedule it shows is a trial schedule.
Unit conventions
All doses are expressed in milligrams of retatrutide per weekly subcutaneous injection; the same unit Lilly uses in the TRIUMPH protocols. Steps are 2 → 4 → 8 → 12 mg, in 4-week blocks.
This is roughly an order of magnitude higher than semaglutide's milligram doses (0.25 → 2.4 mg weekly) and similar in absolute terms to tirzepatide (2.5 → 15 mg weekly), reflecting differences in receptor binding affinity and the triple-target pharmacology rather than potency comparisons. Cross-class milligram numbers should not be read as equivalences; a milligram of retatrutide is not biologically interchangeable with a milligram of semaglutide.
The chart does not produce a volume-in-units conversion. Without an FDA-approved pen concentration, there is no canonical mg-to-units mapping to publish. If retatrutide reaches market with branded pens, that conversion will become a follow-up addition.
Why this is documentary, not prescriptive
The retatrutide dosage chart is a research artifact, not a prescription. It exists because the Phase 2 and Phase 3 escalation schedule is published, well-characterized, and asked about constantly; but the compound itself is not yet a medication anyone can be prescribed in the United States, and the dose-finding work that defines a real label is still ongoing.
Apotheon's editorial position: documenting how a trial protocol is structured is in scope; recommending that any individual reader take a research-grade peptide outside an approved indication is not. The chart shows what has been studied. It does not tell anyone to do it. When retatrutide is approved and a label exists, the page will update to reflect the labeled dose range, contraindications, and any black-box warnings the FDA assigns. Until then, the conservative read is the right one: a promising triple agonist with the largest weight-loss numbers seen in the incretin class so far, a real and not-fully-explained dysesthesia signal, and no FDA approval.
PMIDs on this page were verified live against PubMed before publication by the same INT-01 citation guardrail that gates the calculators on this site.