# Retatrutide Dosage in Clinical Research

> Retatrutide dosage in clinical research: Phase 1 (0.5–12 mg), Phase 2 (1–12 mg once weekly), Phase 3 TRIUMPH (4, 9, 12 mg). Dose-escalation schedules, pharmacokinetics, and administration route.

**Note:** Retatrutide has no approved indication as of mid-2026. All dosage figures describe clinical research protocols, not prescribing guidance.

## Dose Levels Studied Across the Trial Program

Retatrutide dosage in clinical research has ranged from 0.5 mg to 12 mg administered once weekly by subcutaneous injection [5, 1, 2, 9].

| Trial phase | Doses studied | Duration | Key dosage outcome |
|-------------|--------------|----------|-------------------|
| Phase 1b (T2D) | 0.5, 1, 3, 6, 9, 12 mg once weekly | 12 weeks | Dose-proportional PK; −8.96 kg at 9 mg [5] |
| Phase 2 obesity | 1, 4, 8, 12 mg once weekly | 48 weeks | −7.2% (1 mg) to −24.2% (12 mg) [1] |
| Phase 2 T2D | Up to 12 mg once weekly | 36 weeks | −16.9% weight; HbA1c −2.02% [4] |
| Phase 3 TRIUMPH-1 | 4, 9, 12 mg once weekly | 80 weeks | 4 mg: −19.0%; 9 mg: −25.9%; 12 mg: −28.3% [9] |
| Phase 3 TRIUMPH-4 | 9, 12 mg once weekly | 68 weeks | 12 mg: −28.7% [10] |

## Dose-Escalation Schedule

The standard approach used in the TRIUMPH Phase 3 program initiates treatment at 2 mg once weekly, then escalates every 4 weeks until the assigned maintenance dose (4 mg, 9 mg, or 12 mg) is reached [9]. GI adverse events — most prominent in early treatment weeks — are managed to acceptable rates through this escalation approach.

The dose-dependent efficacy signal is strong and monotonic: each step up in maintenance dose produced a larger mean weight reduction in both Phase 2 and Phase 3 data [1, 9, 11].

## How Is Retatrutide Administered?

Subcutaneous injection, once weekly — the only route of administration studied in all published Phase 1–3 clinical data [5, 1, 4, 9]. No oral formulation has been reported.

## Retatrutide Half-Life and Pharmacokinetics

The terminal plasma half-life of Retatrutide is approximately **6 days** in human Phase 1b pharmacokinetic data (Urva et al., Lancet 2022) [5]. Pharmacokinetics are dose-proportional across 0.5 mg to 12 mg.

The C20 fatty diacid conjugation attached via a lysine-17 linker enables non-covalent albumin binding, dramatically slowing renal clearance and proteolytic degradation [14]. Peak plasma concentration is achieved 12–72 hours post-subcutaneous injection. Hepatic metabolism proceeds without CYP450 enzyme involvement [14].

## How Long Does Retatrutide Take to Work?

In Phase 2 obesity trial data:
- Meaningful appetite suppression: within the first 4 weeks
- Statistically significant weight reduction: detectable by approximately week 8
- Maximum weight loss: accrued progressively over 48 weeks; no plateau observed at 48 weeks in the 12 mg group [22]

In Phase 3 TRIUMPH-1 (80 weeks), weight trajectory continued to accrue through the observation window; approximately 30.3% mean reduction in participants with BMI ≥35 reached at 104 weeks [9].

## References

[1] Jastreboff AM, et al. Triple–Hormone-Receptor Agonist Retatrutide for Obesity. N Engl J Med. 2023;389:514-526.
[2] Same source, dose-response at 24 weeks.
[4] Rosenstock J, et al. Retatrutide for T2D. Lancet. 2023.
[5] Urva S, et al. LY3437943 Phase 1b. Lancet. 2022;400:1869-1881.
[9] Eli Lilly. TRIUMPH-1 Phase 3 press release. 2026.
[10] Eli Lilly. TRIUMPH-4 Phase 3 press release. 2025.
[11] Abouelmagd AA, et al. Systematic review and meta-analysis. Proc (Bayl Univ Med Cent). 2025.
[14] Katsi V, et al. Retatrutide—A Game Changer in Obesity Pharmacotherapy. Biomolecules. 2025.
[22] Jastreboff AM, et al. Same as [1], onset and time-course data.

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Plain-language summaries of the Phase 2 and Phase 3 Retatrutide trial record — independent, cited, and not a clinical service.