Weight-loss trajectory (Phase 2)
Continued to increase from 24 to 48 weeks at every dose level tested, without an observed plateau at 48 weeks in the highest-dose groups.
Protocol / Research Dosing Guide
Retatrutide Dosage Guide: Phase 3 Titration, Phase 2 Trial Data and Reconstitution
An evidence-organized retatrutide reference that keeps the Phase 3 TRIUMPH titration design separate from the earlier Phase 2 dose arms and from any personal-use claim, since retatrutide remains investigational.
Last reviewed September 16, 202618 minute readResearch information only
Level 5 — Multiple positive Phase 3 topline resultsNot yet FDA approvedInvestigational triple receptor agonist
Retatrutide Quick Start
Retatrutide (LY3437943) is Eli Lilly's investigational triple hormone receptor agonist, activating GIP, GLP-1 and glucagon receptors. The 2023 Phase 2 obesity trial reported the largest average weight loss yet published for a pharmacologic agent in a 48-week trial, and subsequent Phase 3 TRIUMPH and TRANSCEND programs have reported positive topline results in obesity, knee osteoarthritis and type 2 diabetes. It is not FDA approved, and reported dosing described here reflects clinical-trial and company press-release designs, not an approved label or a personal treatment recommendation.
Why researchers care
Obesity, type 2 diabetes, knee osteoarthritis and metabolic dysfunction-associated steatotic liver disease
Class
Investigational once-weekly triple GIP, GLP-1 and glucagon receptor agonist (LY3437943)
Route reported
Subcutaneous injection in all published and reported trials
Cycle length
Once weekly, with dose escalation over 4-week steps in the Phase 3 design
Regulatory status
Not FDA approved as of the review date; Phase 3 programs are complete or ongoing and no approval decision has been finalized
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Retatrutide Dosing Protocol and Schedule
The supplied source separates the Phase 3 TRIUMPH titration, which starts at 2 mg once weekly and increases every four weeks toward an assigned 4 mg, 9 mg or 12 mg target, from the 2023 Phase 2 trial, which used several parallel starting-dose and target-dose arms (including a fixed 1 mg arm) rather than one universal ladder, over a 48-week study.
| Phase or study | Amount | Frequency / evidence |
|---|---|---|
| Phase 3 TRIUMPH, Weeks 1–4 | 2 mg once weekly | Phase 3 trial design |
| Phase 3 TRIUMPH, Weeks 5–8 | 4 mg once weekly | Phase 3 trial design; also a target dose in TRIUMPH-1/2 |
| Phase 3 TRIUMPH, Weeks 9–12 | 6 mg once weekly | Phase 3 trial design, intermediate step |
| Phase 3 TRIUMPH, Weeks 13–16 | 9 mg once weekly | Phase 3 trial design; target dose in the initial program |
| Phase 3 TRIUMPH, Weeks 17+ | 12 mg once weekly | Phase 3 trial design; highest target dose |
| Phase 2 obesity trial (2023) | 1 mg, 4 mg, 8 mg or 12 mg target arms with 1, 2 or 4 mg starting doses | Jastreboff et al., NEJM 2023 |
The Phase 3 TRIUMPH escalation is a single ladder toward a participant's assigned target dose; participants assigned a 4 mg or 9 mg target stop escalating at that dose rather than continuing to 12 mg. The 2023 Phase 2 trial is sometimes summarized online as one continuous 1-to-12 mg schedule; that is not how the trial was designed, and the two programs should not be merged into a single table.
Retatrutide Supplies Needed
Neutral research-material planning only. This does not establish an appropriate amount or route.
Research planning item
Exact labeled research vial
Research planning item
Bacteriostatic water at a measured volume
Research planning item
U-100 insulin syringes
Research planning item
Alcohol prep swabs
Research planning item
Sharps container
Research planning item
Refrigeration for the prepared vial
Research planning item
Written concentration label with the preparation date
Retatrutide Reconstitution Calculator
Vial-format concentration math
Concentration
6 mg/mL
Draw volume
0.333 mL
U-100 units
33.33
Mathematical draws
6
Arithmetic only. The entered amount is not a recommendation and does not establish suitability.
Best Time to Take Retatrutide: Morning or Night?
Which day of the week?
Once weekly, on a consistent day, is the pattern used in all published trials.
With food?
Not specifically addressed as a requirement in the published trial designs.
Missed weekly dose?
No FDA-approved label exists to define a missed-dose window; trial protocols are not a substitute for approved dosing instructions.
Escalation pace?
Phase 3 TRIUMPH escalated every 4 weeks; this pace was set by trial design, not by an individualized tolerability rule.
Retatrutide Route Comparison
| Format | What is reported | Evidence limit |
|---|---|---|
| Subcutaneous injection | Once weekly in Phase 2 and Phase 3 trials | The only route studied in any published or announced trial |
| Oral | No published oral retatrutide human trial was identified | Not established |
| Route conversion | Not applicable | Only one route has been studied |
Routes and amounts are not interchangeable unless a verified study explicitly establishes a conversion.
Retatrutide Half-Life and Dosing Frequency
| Measure | Finding | Evidence limit |
|---|---|---|
| Human half-life | Consistent with a once-weekly dosing interval as used in trials | A specific published half-life figure was not identified in the sources reviewed; frequency is inferred from trial design, not cited independently here |
| Steady-state timing | Reached after the trial's stepwise escalation reaches the target dose (around 16 weeks or later for the highest target) | Trial-design based |
| Cross-trial consistency | Once-weekly frequency has been consistent from the earliest published mechanism paper (Coskun 2022) through Phase 3 | Preclinical and clinical program consistency |
| Renal/hepatic adjustment | Not established in the sources reviewed | No published dose-adjustment guidance exists because there is no approved label |
Retatrutide Dosage Chart
| Route | Amount | Frequency | Source | Human validation |
|---|---|---|---|---|
| Subcutaneous | 1 mg | Once weekly | Phase 2 fixed arm | No |
| Subcutaneous | 4 mg | Once weekly | Phase 2 and Phase 3 target/step dose | No |
| Subcutaneous | 8 mg | Once weekly | Phase 2 target dose | No |
| Subcutaneous | 9 mg | Once weekly | Phase 3 target dose | No |
| Subcutaneous | 12 mg | Once weekly | Phase 2 and Phase 3 highest target dose | No |
Published study values describe those studies. Community-reported values are not validated dosing recommendations.
Retatrutide Reconstitution Guide
Concentration: 6 mg/mL
| Entered amount | Volume | U-100 units |
|---|---|---|
| 2 mg | 0.333 mL | 33.33 units |
| 4 mg | 0.667 mL | 66.67 units |
| 6 mg | 1 mL | 100 units |
- 1.Confirm the exact quantity printed on the vial.
- 2.Choose and record the bacteriostatic water volume, and calculate concentration precisely.
- 3.Clean the stopper with an alcohol swab.
- 4.Add the liquid slowly down the vial wall.
- 5.Swirl gently until clear; never shake.
- 6.Inspect for cloudiness, color or particles and discard anything that is not clear.
- 7.Label the vial with the concentration and the preparation date.
- 8.Refrigerate the prepared vial and use only the calculated concentration for arithmetic; no FDA-approved stability window exists for a research-labeled vial.
Reconstitution does not establish identity, purity, sterility, stability, or an appropriate amount.
How Retatrutide Works
Receptor profile
Retatrutide is a single peptide agonist at three receptors: GIP, GLP-1 and glucagon.
Retatrutide Human Trials and FDA Status
Current status · verified September 16, 2026
Not FDA approved as of the review date; Phase 3 programs are complete or ongoing and no approval decision has been finalized
- Jastreboff et al., NEJM 2023: a 48-week, randomized, placebo-controlled Phase 2 trial in 338 adults with obesity or overweight reported mean weight loss up to 24.2% at the highest 12 mg dose at 48 weeks, versus 2.1% with placebo.
- Sanyal et al., Nature Medicine 2024: a Phase 2a trial in metabolic dysfunction-associated steatotic liver disease reported reductions in liver fat with retatrutide.
- TRIUMPH-4 (Eli Lilly topline, 2025): a Phase 3 trial in participants with obesity and knee osteoarthritis reported average weight loss of up to 71.2 lbs and relief from osteoarthritis pain.
- TRIUMPH-1 and additional TRIUMPH Phase 3 obesity trials (Eli Lilly topline, 2026): reported significant improvements in weight and glycemic measures.
- TRANSCEND-T2D-1 (Eli Lilly topline, 2026): the first Phase 3 trial in adults with type 2 diabetes reported significant reductions in A1C and body weight.
- As of the review date, retatrutide has not received FDA approval; company press releases and topline announcements are not equivalent to a peer-reviewed publication or a regulatory decision.
Who Should Avoid Retatrutide?
This is an evidence-gap and precaution list, not an approved prescribing label.
Personal history or family history of medullary thyroid carcinoma or MEN2
This is a standard precaution for the incretin-based drug class; retatrutide-specific labeling does not exist because it is not approved
Pregnancy or breastfeeding
No human safety data exists for this investigational compound
Active pancreatitis
Raised as a class-level concern for GLP-1/GIP/glucagon agonists; retatrutide-specific incidence is not established outside trial safety reporting
Use outside a clinical trial or licensed prescriber oversight
Retatrutide sold as a research chemical is not the same regulated product studied in Lilly's trials, and its identity, purity and dosing cannot be verified the way an approved drug can
Children or adolescents
Not studied in this population in the sources reviewed
Reliance on a self-administered escalation without medical supervision
The published Phase 3 escalation was managed within a monitored clinical trial, not a self-directed program
Retatrutide Side Effects, Risks and Safety
Gastrointestinal effects (nausea, vomiting, diarrhea, constipation)Common in Phase 2 and Phase 3 trials
Important limitation: Consistent with the GLP-1/GIP mechanism class and dose-dependent, similar to other incretin-based agents.
Increased heart rateReported in the Phase 2 trial
Important limitation: Monitored as part of trial safety assessments.
Injection-site reactionsReported
Important limitation: Consistent with subcutaneous peptide administration.
Gallbladder-related eventsA class-level concern with significant weight loss from incretin therapies
Important limitation: Retatrutide-specific incidence has not been fully characterized in a completed regulatory review.
Long-term safety beyond the published 48-week Phase 2 windowNot established through peer-reviewed publication as of the review date
Important limitation: Longer Phase 3 data exists in company announcements but full peer-reviewed long-term safety publications were not identified in the sources reviewed.
Unregulated research-chemical supplyPurity, dose accuracy and sterility cannot be verified outside the clinical trial supply chain
Important limitation: Distinct from the compound studied in Lilly's trials.
Retatrutide Timeline and Monitoring
Dose-escalation timeline (Phase 3)
Four-week steps from 2 mg toward the assigned target dose of 4, 9 or 12 mg.
Approval timeline
Not established; multiple Phase 3 programs have reported positive topline results but a completed FDA review and approval had not occurred as of the review date.
Monitoring
Trial protocols included monitoring for gastrointestinal tolerability, heart rate and standard laboratory safety parameters; no FDA-approved label monitoring schedule exists yet.
Retatrutide Benefits and Results: What the Evidence Shows
| Claim | Evidence level | What research shows | Important limitation |
|---|---|---|---|
| Weight loss in adults with obesity or overweight | Phase 2 and multiple Phase 3 topline reports | NEJM 2023 and Lilly TRIUMPH program announcements | Not yet an FDA-approved indication |
| Glycemic improvement in type 2 diabetes | Phase 3 topline report | TRANSCEND-T2D-1 topline announcement | Not yet peer-reviewed in full or FDA approved |
| Reduction in liver fat (MASLD) | Phase 2a human trial | Sanyal et al., Nature Medicine 2024 | Small trial; not an approved indication |
| Osteoarthritis pain relief tied to weight loss | Phase 3 topline report | TRIUMPH-4 topline announcement | Topline press release, not yet a full peer-reviewed publication at the time of this review |
Retatrutide Storage and Handling
Lyophilized research vial
No FDA-approved storage guidance exists; any research-labeled vial should follow its own product label, which cannot be independently verified.
Reconstituted vial
No FDA-approved reconstituted-stability data exists for a research vial; refrigeration and short use windows are typical peptide-handling precautions, not verified retatrutide-specific data.
Clinical trial drug product
Storage conditions used in Lilly's trials are not publicly detailed at the vial level in the sources reviewed.
Appearance
A clear, colorless solution is the general expectation for reconstituted peptides; cloudiness or particles mean discard.
Retatrutide Troubleshooting
Confusing Phase 2 and Phase 3 schedules
Keep the two programs separate: Phase 2 used several parallel dose arms; Phase 3 TRIUMPH uses one escalation ladder toward an assigned target.
Solution appears cloudy
Discard and do not inject; appearance cannot confirm sterility or identity in an unregulated research vial.
Calculated units look wrong
Recheck vial quantity, diluent volume, target amount and U-100 conversion.
Assuming press-release results are equivalent to an approved label
Company topline announcements are not the same as a peer-reviewed publication or an FDA-approved label; treat them as preliminary.
Unexpected symptoms occur
No FDA-approved retatrutide safety protocol exists yet; seek licensed clinical review.
Retatrutide Comparisons
| Compound | Class or mechanism | Evidence | FDA status |
|---|---|---|---|
| Retatrutide | Triple GIP/GLP-1/glucagon agonist | Phase 2 published; multiple positive Phase 3 toplines | Investigational; not FDA approved |
| Tirzepatide | Dual GIP/GLP-1 agonist | Extensive Phase 3 program | FDA approved (Zepbound/Mounjaro) |
| Semaglutide | GLP-1 agonist | Extensive Phase 3 program | FDA approved (Wegovy/Ozempic) |
| Cagrilintide | Amylin analogue, often studied in combination | Phase 2/3 combination trials ongoing | Investigational; not FDA approved as monotherapy |
Retatrutide Frequently Asked Questions
What is retatrutide?
An investigational once-weekly injectable peptide that activates GIP, GLP-1 and glucagon receptors, developed by Eli Lilly under the code LY3437943.
Is retatrutide FDA approved?
No. As of the review date it remains investigational, even though multiple Phase 3 trials have reported positive topline results.
What was the Phase 2 starting dose?
The 2023 Phase 2 trial used several parallel arms with 1, 2 or 4 mg starting doses depending on the assigned target dose, not one universal starting dose.
What is the Phase 3 TRIUMPH starting dose?
2 mg once weekly, with escalation every four weeks toward an assigned 4 mg, 9 mg or 12 mg target.
How much weight loss was reported in Phase 2?
Up to a mean of 24.2% of body weight at 48 weeks in the highest 12 mg dose group, compared with 2.1% for placebo.
Has it been studied for diabetes?
Yes; the TRANSCEND-T2D-1 Phase 3 trial reported topline reductions in A1C and weight, but full peer-reviewed results and FDA review status should be confirmed independently of a press release.
What is its half-life?
A specific human half-life figure was not identified in the sources reviewed; once-weekly dosing has been consistent from early preclinical work through Phase 3.
What are the most common side effects?
Gastrointestinal effects such as nausea, vomiting, diarrhea and constipation, consistent with the incretin drug class, plus increased heart rate reported in trials.
Is retatrutide sold as a research chemical the same as the trial drug?
No. Research-chemical products are not part of Lilly's regulated clinical trial supply chain, and their identity, purity and dosing accuracy cannot be independently verified the way an approved drug can.
Is there a validated maintenance dose?
No FDA-approved maintenance dose exists; Phase 3 target doses of 4, 9 and 12 mg were assigned by trial design, not by an individualized dosing rule.
What does the calculator do?
For a non-approved research vial, it converts entered vial and liquid values into concentration and volume math only; it does not establish a personal dose or substitute for a completed regulatory review.
Sources and Research
Coverage source
1. Retatrutide protocol coverage source
Phase 2/Phase 3 titration tables, reconstitution math and quick-start categories; not primary regulatory or trial evidence.
Open direct sourceHuman research
2. Triple-Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial
Jastreboff et al., NEJM 2023; 48-week randomized, placebo-controlled Phase 2 trial establishing dose-dependent weight loss.
Open direct sourceLaboratory and translational research
3. LY3437943, a novel triple glucagon, GIP, and GLP-1 receptor agonist for glycemic control and weight loss: From discovery to clinical proof of concept
Coskun et al. 2022; preclinical discovery and mechanism paper supporting the triple-agonist rationale.
Open direct sourceHuman research
4. Triple hormone receptor agonist retatrutide for metabolic dysfunction-associated steatotic liver disease: a randomized phase 2a trial
Sanyal et al., Nature Medicine 2024; Phase 2a trial reporting liver-fat reduction.
Open direct sourceTrial registry
5. TRANSCEND-T2D-1: A Study of Retatrutide (LY3437943) in Adult Participants With Type 2 Diabetes (NCT06354660)
ClinicalTrials.gov registration for the Phase 3 type 2 diabetes trial referenced in company topline announcements.
Open direct sourceMissing information flagged for review
- FDA approval and an approved label: Not established
- Full peer-reviewed publication of most Phase 3 TRIUMPH and TRANSCEND results: Not established
- Long-term safety data beyond the published 48-week Phase 2 window: Not established
- Verified identity, purity and dosing accuracy for research-chemical retatrutide products: Not established
- Pediatric and pregnancy safety data: Not established
- A single, harmonized dosing schedule across indications: Not established