Retatrutide Dosing Protocol: 5 mg Vial — Week-by-Week Titration & Supplies
Quickstart highlights
Retatrutide (LY3437943, Eli Lilly) is a once-weekly GLP-1/GIP/glucagon receptor triagonist with 24.2% mean body weight reduction at 48 weeks in Phase 2 (NCT04881760, 12 mg arm) — the highest weight loss reported for any anti-obesity drug to date.
- Concentration: 5 mg/mL (5 mg vial + 1 mL bacteriostatic water).
- At 5 mg/mL: 1 mg = 20 units, 2 mg = 40 units, 4 mg = 80 units, 5 mg = 100 units.
- Phase 2 trial: 12 mg dose produced 24.2% mean body weight reduction at 48 weeks — highest for any anti-obesity drug studied to date.
- One 5 mg vial provides 5 starting doses at 1 mg, or 1 dose at 4 mg maintenance.
- Doses above 5 mg require two vials per injection; consider higher-mg vials for maintenance.
Dosing table
For educational reference only. Your prescribing provider may adjust doses based on your clinical profile and response.
| Week | Dose (µg) | Units | Frequency | Notes |
|---|---|---|---|---|
| 1-4 | 1000 | 20 | Once weekly | 1 mg starting dose — 20 units on U-100 syringe; one 5 mg vial provides 5 doses |
| 5-8 | 2000 | 40 | Once weekly | 2 mg dose — 40 units; vial provides 2–3 doses at this level |
| 9-12 | 4000 | 80 | Once weekly | 4 mg dose — 80 units; assess tolerability before advancing |
| 13+ | 8000 | 160 | Once weekly | 8 mg maintenance — requires 2 vials (160 units at 5 mg/mL = 1.6 mL; use two separate draws or reconstitute higher concentration) |
Gradual approach
| Week | Dose (µg) | Units | Notes |
|---|---|---|---|
| 1-8 | 1000 | 20 | Slow ramp — hold 1 mg x 8 weeks to minimize GI side effects |
| 9-12 | 2000 | 40 | 2 mg for 4 weeks before advancing |
Your free Retatrutide tracker
- Dose reminders
- Injection logging
- Cycle progress
Reconstitution steps
- Draw 1 mL bacteriostatic water; inject slowly down the vial wall to prevent foaming.
- Swirl gently until lyophilized powder fully dissolves (1–3 minutes); avoid shaking.
- Final concentration: 5 mg/mL. At this concentration, doses above 5 mg require combining two vials.
- Label with date and concentration; refrigerate at 2–8 °C immediately.
Supplies needed
8-week plan
- 2 vials
- 8 syringes
- 2 mL bac water
- 8 alcohol swabs
12-week plan
- 3 vials
- 12 syringes
- 3 mL bac water
- 12 alcohol swabs
16-week plan
- 5 vials
- 16 syringes
- 5 mL bac water
- 16 alcohol swabs
Protocol overview & cycle notes
Initiate the retatrutide triple agonist protocol at 1 mg weekly, titrating to 4–8 mg maintenance over 12 weeks to capture the superior weight loss potential of GLP-1/GIP/glucagon co-agonism while minimizing GI adverse effects.
Cycle length: 16 weeks on.
Off-cycle: 8–12 weeks off; monitor weight, appetite, and metabolic labs during off-cycle.
Storage & handling
Injection & tracking tips
- Rotate injection sites (abdomen, thigh, upper arm) every week to minimize local reactions.
- For the 8 mg dose (160 units at 5 mg/mL = 1.6 mL), draw into a 3 mL syringe combining volume from two fresh vials on injection day.
- Retatrutide's glucagon agonism increases thirst and urination — ensure adequate hydration (2.5+ L/day) at doses ≥4 mg.
Tracking
Logging helps you and your provider spot patterns and adjust dose or timing.
- Log body weight every Monday fasted; expect 1–3% loss per month at therapeutic doses.
- Record nausea and GI symptom severity (0–10) weekly for the first 12 weeks.
- Track fasting glucose weekly; glucagon agonism can transiently affect blood sugar regulation.
How this works & references
Sources
- Triple-Hormone-Receptor Agonist Retatrutide for Obesity - A Phase 2 Trial. Jastreboff AM et al. — N Engl J Med — 2023
- TRIUMPH Phase 3 trials (NCT05668520) — Retatrutide ongoing Phase 3 for obesity
- Retatrutide, a GIP, GLP-1 and glucagon receptor agonist, for people with type 2 diabetes: a randomised, double-blind, placebo and active-controlled, parallel-group, phase 2 trial conducted in the USA. Rosenstock J et al. — Lancet — 2023
- Effects of retatrutide on body composition in people with type 2 diabetes: a substudy of a phase 2, double-blind, parallel-group, placebo-controlled, randomised trial. Coskun T et al. — Lancet Diabetes Endocrinol — 2025
Frequently asked questions
How does retatrutide compare to tirzepatide for weight loss?
What GI side effects should I expect with retatrutide?
Is retatrutide FDA-approved?
Why does my 8 mg dose require two vials?
Does retatrutide affect liver health?
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