What Is Reta? The Reta (Retatrutide) Peptide Explained
Reta is the shorthand people use for retatrutide (LY-3437943) — a triple GLP-1 / GIP / glucagon receptor agonist peptide developed by Eli Lilly and currently in Phase 3 trials. If you have seen "reta" mentioned alongside tirzepatide and semaglutide, it is the same compound as retatrutide, just abbreviated.
This page answers the questions people actually ask about reta — what it is, how it works, how it compares to Mounjaro and other GLP compounds, how it is stored and reconstituted, and what it costs in the UK. For In Vitro Use Only — Not for Human Use.
Reta vs retatrutide — is there a difference?
No. Reta and retatrutide are the same peptide. "Reta" is community shorthand, the same way tirzepatide is shortened to "tirz" and semaglutide to "sema". The research code is LY-3437943.
Anything you read about retatrutide dosing, purity, reconstitution or storage applies exactly to reta. Full background is on our retatrutide UK hub.
How reta works — the triple agonist mechanism
| Compound | Receptors targeted | Class |
|---|---|---|
| Semaglutide (sema) | GLP-1 | Single agonist |
| Tirzepatide (tirz) | GLP-1 + GIP | Dual agonist |
| Retatrutide (reta) | GLP-1 + GIP + glucagon | Triple agonist |
The glucagon-receptor arm is what sets reta apart — it is associated in published literature with increased energy expenditure, on top of the two incretin pathways. Read the direct comparisons: reta vs tirzepatide and reta vs semaglutide.
Reta vials, strengths and UK price
| Reta vial | Price | Cost per mg |
|---|---|---|
| Reta 20mg | £89.00 | £4.45/mg |
| Reta 30mg | £119.00 | £3.97/mg |
| Reta 40mg | £154.00 | £3.85/mg |
Vials are the cheapest format — a pre-filled pen adds £34.99 for the hardware and preparation. Full figures on the retatrutide price page, or buy direct from the retatrutide vials page.
Storing and reconstituting reta
- Add bacteriostatic water slowly down the vial wall — never shake.
- Most protocols use 1–3mL of bacteriostatic water per vial depending on concentration.
- Store reconstituted vials at 2–8°C and use within 28 days. Do not freeze.
- Keep unopened lyophilised vials cool, dark and dry.
- Dose with a U-100 insulin syringe and work out units with the calculator.
Use the free reconstitution calculator for exact volumes, or read the full reconstitution guide.
Buying reta in the UK
- UK stock — no customs, no overseas reshippers, no seizure risk.
- Same-day dispatch before 2pm Monday to Friday, Royal Mail Tracked 24.
- Independently HPLC tested with a batch-matched Certificate of Analysis.
- Discreet plain packaging on every order.
Verify any batch on our COA page before you order.
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View full shopFrequently asked questions
What is reta?
"Reta" is the everyday shorthand for retatrutide (LY-3437943), an investigational triple receptor agonist peptide developed by Eli Lilly. It activates the GLP-1, GIP and glucagon receptors in a single molecule. Reta and retatrutide are the same compound — reta is simply the abbreviation used in research and peptide communities. For In Vitro Use Only — Not for Human Use.
What is reta peptide?
Reta peptide is retatrutide supplied as a lyophilised (freeze-dried) powder in a sealed glass vial, reconstituted with bacteriostatic water before laboratory use. It is a research peptide, not a licensed medicine, and is sold in the UK for in vitro research only.
How does reta work?
Retatrutide engages three receptor pathways at once. GLP-1 activation influences satiety and insulin signalling, GIP adds a second incretin pathway, and glucagon-receptor activation is associated in published literature with increased energy expenditure. Semaglutide targets one receptor and tirzepatide two, which is why reta is described as a triple agonist.
Is reta better than Mounjaro?
Mounjaro is a licensed tirzepatide medicine (dual GLP-1/GIP). Retatrutide is an unlicensed triple agonist still in Phase 3 trials, so no regulator has compared them head to head for clinical use. Eli Lilly's published Phase 2 data reported the largest weight-related endpoints of any GLP-family compound at that stage, but reta is a research compound only and is not an alternative to a prescribed medicine.
Is reta a steroid?
No. Reta is a peptide — a short chain of amino acids that binds incretin and glucagon receptors. It is not an anabolic steroid and shares no mechanism with steroid hormones.
Is reta legal in the UK?
Retatrutide is legal to buy and possess in the UK for laboratory research purposes. It is not a licensed medicine and cannot be prescribed on the NHS or privately. It is supplied strictly For In Vitro Use Only — Not for Human Use.
How much reta is in each vial?
Peptides UK 4U supplies reta in 20mg, 30mg and 40mg vials — £89.00, £119.00 and £154.00 respectively, which is £4.45, £3.97 and £3.85 per mg. Every batch is independently HPLC tested with a batch-matched Certificate of Analysis.
How much does reta cost?
Reta costs from £3.85 per mg in the UK. A 20mg vial is £89.00, 30mg is £119.00 and 40mg is £154.00. The full breakdown, including cost per month at different weekly amounts, is on our retatrutide price page.
How do you reconstitute reta?
Add bacteriostatic water slowly down the inside wall of the vial and let it dissolve — never shake. Typical research protocols use 1–3mL per vial depending on the concentration needed. Our free reconstitution calculator works out the exact units on a U-100 syringe for any vial size and water volume.
Does reta need to be refrigerated?
Unopened lyophilised vials are stable at room temperature for short periods and are best kept cool, dark and dry. Once reconstituted, store at 2–8°C and use within 28 days. Do not freeze a reconstituted vial.
How long does reta take to work?
In published Phase 2 trial data, measurable endpoints appeared over a course of weeks rather than days, with effects increasing across the titration period. This describes published research findings only — reta is not for human use.
Where can I buy reta in the UK?
Peptides UK 4U holds reta (retatrutide) vials in UK stock with same-day dispatch before 2pm Monday to Friday by Royal Mail Tracked 24. No customs, no overseas reshippers, and a batch-matched COA with every order.
Disclaimer: All products sold by Peptides UK 4U are for laboratory and research purposes only. They are not intended for human or animal consumption, diagnosis, treatment or prevention of any disease.