What Dose Was Used in Phase 2 Trials?
The SURMOUNT-like Phase 2 trial for Retatrutide tested three dose levels: 4 mg, 8 mg, and 12 mg, administered once weekly via subcutaneous injection. The 8 mg and 12 mg arms produced the most significant weight reduction — an average of 17.5% and 22.8% body weight loss respectively at 48 weeks.
For research purposes, these trial protocols are the primary reference points. Researchers studying metabolic peptides typically begin with the lowest effective dose and titrate upward based on individual tolerance and response.
Starting Dose Protocol
Research protocols based on Phase 2 data typically start at 2 mg once weekly for weeks 1–4. This initiation dose is well below the therapeutic range used in trials but allows the gastrointestinal system to adapt, dramatically reducing nausea, vomiting, and other GI side effects at the onset.
| Week | Dose | Notes |
|---|---|---|
| 1–4 | 2 mg | Initiation — GI tolerance |
| 5–8 | 4 mg | Phase 2 lower-arm dose |
| 9–12 | 6 mg | Intermediate bridge dose |
| 13–16 | 8 mg | Primary Phase 2 effective dose |
| 17+ | 8–12 mg | Maintenance range |
Injection Frequency
Retatrutide was administered once weekly in all Phase 2 arms. This is consistent with its pharmacokinetic profile — the compound has a half-life of approximately 6 days, making weekly injection ideal for maintaining stable plasma concentrations without accumulation.
Some research protocols explore bi-weekly administration at higher doses (12–16 mg every two weeks), which mirrors the pharmacokinetics approximately. However, weekly administration at lower doses generally produces superior GI tolerability.
Reconstitution for Research
Retatrutide vials from QSC are supplied as lyophilized powder, typically in 2 mg or 10 mg configurations. To reconstitute for research use, add bacteriostatic water (BAC water) slowly to the vial by directing liquid down the inner glass wall — never inject directly onto the peptide cake.
For a 10 mg vial: adding 2 mL BAC water produces a 5 mg/mL (5,000 mcg/mL) solution. Each 0.1 mL (10 units on an insulin syringe) = 500 mcg. Reconstituted vials should be stored at 2–8°C and used within 28 days.
Dose Calculation Table
| Target Dose | From 5 mg/mL solution | Syringe Volume |
|---|---|---|
| 2 mg (2000 mcg) | 0.4 mL | 40 units |
| 4 mg (4000 mcg) | 0.8 mL | 80 units |
| 6 mg (6000 mcg) | 1.2 mL | 120 units |
| 8 mg (8000 mcg) | 1.6 mL | 160 units |
| 12 mg (12000 mcg) | 2.4 mL | 240 units |
Holding and Adjusting Doses
In Phase 2 trials, participants who experienced Grade 2 or higher GI adverse events had their dose escalation paused for 4 weeks. Research protocols commonly adopt the same approach: if significant nausea or vomiting occurs at a given dose, hold at that level for an additional 4–8 weeks before attempting to escalate.
Unlike GLP-1 mono-agonists, Retatrutide's triple mechanism (GLP-1 + GIP + glucagon receptor) means that GI side effects can be more pronounced during initiation but typically diminish significantly by weeks 8–12.
Source Research-Grade Retatrutide
QSC Retatrutide (RT10) — 10 mg vials, ≥99% HPLC purity, Janoshik COA on every batch. Domestic US, EU, UK, AU, CA, and Asia warehouses.
View Retatrutide at QSC →