Retatrutide Quick Start
Retatrutide is an investigational triple agonist that activates the GLP-1, GIP, and glucagon receptors. It is studied for weight management and metabolic outcomes and has produced large weight-reduction effects in trials. It is dosed weekly with a gradual titration to manage gastrointestinal side effects. It is investigational (Phase 3 as of 2026).
This guide is an educational research reference. It does not diagnose, treat, or prescribe, and is not medical advice. Consult a licensed clinician before considering any compound.
Retatrutide Dosing Protocols
The injectable (subcutaneous) and nasal-spray formats are documented as two separate protocols. Both follow the same weekly titration ladder — roughly four weeks per step — and can be run as a single weekly dose or split into two doses per week at the same weekly total. Splitting often smooths gastrointestinal side effects. These are research-planning references, not personal dosing recommendations.
Injection — Subcutaneous (U-100 units)
| Phase | Weekly | 1×/wk | 2×/wk |
|---|---|---|---|
| 1 | 2 mg | 20 u | 10 u ×2 |
| 2 | 4 mg | 40 u | 20 u ×2 |
| 3 | 8 mg | 80 u | 40 u ×2 |
| 4 (max) | 12 mg | 120 u* | 60 u ×2 |
Nasal Spray (0.6 mg / spray)
| Phase | Weekly | 1×/wk | 2×/wk |
|---|---|---|---|
| 1 | 2 mg | 4 sprays | 2 ×2 |
| 2 | 4 mg | 7 sprays | 4 ×2 |
| 3 | 8 mg | 14 sprays | 7 ×2 |
| 4 (max) | 12 mg | 20 sprays | 10 ×2 |
Retatrutide Reconstitution Guide
Retatrutide ships as a lyophilized powder. The injection uses the vial at its 3 mL maximum fill (10 mg/mL, 10 units per mg); the nasal spray ships pre-mixed and delivers 0.6 mg per spray, so each dose is spread over more sprays.
Injection (vial)
| BAC | Conc. | 12 mg |
|---|---|---|
| 3 mL | 10 mg/mL | 1.2 mL · 2 draws |
| 2 mL | 15 mg/mL | 0.8 mL · 80 u |
Vial holds up to ~3 mL. 2 mL fits 12 mg in one syringe but gives non-round units. U-100.
Reconstitution steps
- Inspect the vial. Confirm label and intact powder.
- Wipe the stoppers. Alcohol swab on both vials.
- Draw BAC water. 3 mL into the vial for injection (10 mg/mL).
- Inject down the wall. Release water slowly down the inside wall, not onto the powder.
- Swirl, do not shake. Roll gently until clear.
- Refrigerate. Store at 2–8 °C; do not freeze.
How to use the nasal spray
- Prime first use. Pump 2–3 sprays into a tissue until a fine, even mist appears.
- Position. Tilt the head slightly forward; insert the tip just inside one nostril, aimed slightly outward toward the ear — not at the septum.
- Spray and breathe. Press once while breathing in gently; do not sniff hard, which sends the solution down the throat instead of onto the mucosa.
- Alternate nostrils. For multi-spray doses, switch nostrils each spray to spread absorption and limit irritation.
- Count per the protocol. Use the sprays-per-dose shown above; if a dose isn't a whole number, round up.
- Between uses. Wipe the tip, recap, and refrigerate.
How Retatrutide Works
Retatrutide simultaneously activates three incretin/metabolic receptors. GLP-1 and GIP agonism reduce appetite and improve glucose handling, while glucagon-receptor agonism is thought to increase energy expenditure and support fat metabolism. This triple action is the basis for the large weight-reduction effects reported in trials, and the glucagon component differentiates it from GLP-1 and dual GLP-1/GIP agonists.
GLP-1
Appetite reduction and improved glucose-dependent insulin response.
GIP
Complementary incretin effect on glucose and appetite.
Glucagon
Thought to raise energy expenditure and support lipolysis.
Open question
Long-term outcomes and approval status are still being established in Phase 3.
Who Should Avoid Retatrutide
MTC / MEN2 history
Like other incretin agents, a personal/family history of medullary thyroid carcinoma or MEN2 is a key caution.
Pancreatitis history
Incretin agonists carry a pancreatitis caution.
Pregnancy & lactation
Not appropriate; no safety data in this context.
Severe GI disease
Gastroparesis or significant GI disease may be worsened.
Retatrutide Side Effects & Safety
Gastrointestinal
Nausea, vomiting, diarrhea, and constipation are the most common, dose-dependent, and the reason for slow titration.
Heart rate
Modest increases in heart rate have been observed with incretin agents.
Glucose / appetite
Reduced appetite and improved glucose handling; watch for hypoglycemia if combined with other agents.
Titration matters
Escalating too fast worsens GI effects; splitting to twice weekly can smooth them.
Timeline & What to Monitor
| Timeframe | Commonly tracked | Notes |
|---|---|---|
| Weeks 1–4 | GI tolerability at the starting step | Hold or slow escalation if GI effects are strong. |
| Each step (~4 wks) | Tolerability before escalating | Only advance the ladder when the current step is tolerated. |
| Ongoing | Weight, glucose, heart rate | Track the metabolic endpoints and vitals. |
Clinical Evidence Context
Phase 2
A Phase 2 obesity trial reported large dose-dependent weight reductions (Jastreboff et al., NEJM, 2023).
Phase 3 (TRIUMPH)
The Phase 3 program is evaluating efficacy and safety at scale.
Mechanistic novelty
The glucagon component distinguishes it from GLP-1 and GLP-1/GIP agents.
Boundary
Not yet approved; research/investigational context only.
Storage & Handling
| State | Storage | Notes |
|---|---|---|
| Lyophilized (powder) | −20 °C long-term; fridge short-term | More stable than reconstituted solution. |
| Reconstituted (liquid) | 2–8 °C | Use within ~3–4 weeks; do not freeze. |
| Appearance | Clear, colorless | Discard cloudy or particulate solutions. |
Mistakes & Troubleshooting
- Strong nausea. Hold the current step or split to twice weekly; don't escalate until tolerated.
- Escalating too fast. Stay ~4 weeks per step; GI effects track the speed of titration.
- Exact dosing. Spray increments are 0.6 mg and round up, so a spray dose can slightly exceed the target; use the injection for precise amounts.
- Left out overnight. Treat reconstituted solution as compromised and discard.
Retatrutide vs Other Incretin Agents
| Feature | Retatrutide | Semaglutide / Tirzepatide |
|---|---|---|
| Targets | GLP-1 + GIP + glucagon (triple) | GLP-1 (semaglutide) / GLP-1+GIP (tirzepatide) |
| Cadence | Weekly, titrated | Weekly, titrated |
Blood Tests & Monitoring
| Marker | Why | Timing |
|---|---|---|
| Fasting glucose / HbA1c | Metabolic effect and hypoglycemia risk with other agents | Baseline + periodic |
| CMP / lipase | General safety; pancreatitis caution | Baseline / as advised |
| Heart rate / BP | Incretin agents can modestly raise heart rate | Periodic |
Frequently Asked Questions
What is Retatrutide?
An investigational triple agonist (GLP-1/GIP/glucagon) studied for weight and metabolic outcomes. It is dosed weekly with titration and is investigational.
Once-weekly or twice-weekly?
Both, at the same weekly total. The ladder is 2 → 4 → 8 → 12 mg/week (~4 weeks per step). Once-weekly gives the full dose in one injection; twice-weekly splits it in half, which can smooth GI side effects.
How is the injection dosed vs the nasal spray?
Separate protocols. At 10 mg/mL, injection is 10 units per mg (12 mg = 120 u — split into two draws, or run twice-weekly at 6 mg = 60 u). The spray uses a 5 mL fill → 0.6 mg per spray, so the weekly dose is 4–20 sprays (2–10 if split twice-weekly), rounded up to whole sprays.
How is Retatrutide reconstituted?
Injection uses 30 mg in 3 mL BAC water (the vial's max fill) → 10 mg/mL, 10 units per mg. The nasal spray ships pre-mixed and delivers 0.6 mg per spray.
Is this page medical advice?
No. It is an educational research reference and does not diagnose, treat, or prescribe. Consult a licensed clinician before considering any compound.
References
- Jastreboff AM, et al. Triple-hormone-receptor agonist retatrutide for obesity (Phase 2). N Engl J Med (2023).
- Rosenstock J, et al. Retatrutide in type 2 diabetes (Phase 2). Lancet (2023).
- Eli Lilly. TRIUMPH Phase 3 retatrutide program (clinical trial registrations).
- Coskun T, et al. Pharmacology of the triple agonist retatrutide. Cell Metab / Mol Metab (2022).