What Retatrutide is
Retatrutide is an experimental weekly injection from Eli Lilly. It acts on three hormone receptors: GIP and GLP-1, like tirzepatide, plus glucagon. The glucagon piece is thought to increase energy use.
It is the most-searched experimental weight loss drug of 2026. That popularity has created a large gray market for vials labeled "retatrutide" that have nothing to do with Lilly.
Regulatory status in 2026
Retatrutide is not approved. The only legal way to get it is through a clinical trial. Lilly has announced plans to apply for FDA approval, but has not yet filed.
Phase 2 trial results published, showing large weight loss over 48 weeks.
Multiple Phase 3 trials meet their main weight loss goals.
Lilly says it plans to submit retatrutide to FDA in the first quarter of 2027.
Not approved. If filed on schedule, a decision would likely come in late 2027 or 2028.
Regulatory status can change. Check the sources linked at the bottom of this page before relying on anything here.
Claims vs. what the research shows
Unlike most gray-market peptides, retatrutide has strong human data. That data comes from Lilly's manufactured drug, not from what's sold online.
Causes more weight loss than current drugs.
Large weight loss shown in Phase 2 and Phase 3 trials. Head-to-head comparisons with approved drugs are still limited.
Strong human evidenceResearch retatrutide is the same as Lilly's.
No. Gray-market vials have not been tested by FDA and their contents are unknown.
Insufficient dataSafe because it passed trials.
Trials are ongoing, the full safety review hasn't happened, and FDA has not approved it.
Insufficient dataStorage and stability
Peptides break down with heat, light, moisture, and repeated freezing and thawing. Degraded product is one common reason two vials of the "same" peptide behave differently. These are general peptide handling practices. Your supplier's certificate of analysis or label takes priority.
Sealed powder (lyophilized)
- Refrigerate at 36 to 46°F (2 to 8°C) for routine storage.
- Freezer is generally used for long-term storage.
- Keep in its original sealed vial, away from light.
- Let a cold vial reach room temperature before opening to limit condensation.
After reconstitution
- Keep refrigerated. Do not freeze.
- Protect from light. Clear glass lets it through.
- Opened multi-dose bacteriostatic water is typically discarded 28 days after first puncture.
- Log the mix date so you know the vial's age at a glance.
Light exposure is easy to overlook in a fridge door that opens dozens of times a day. VIALTIGHT is building stackable cases that block light from every side. See vialtight.com for updates.
Reconstitution math
Concentration is just the amount of peptide divided by the volume of water added. On a U-100 insulin syringe, 100 units equals 1 mL, so each unit is 0.01 mL. Enter what is on your vial label and what you added to see the concentration.
This shows concentration only. It is not a dosing recommendation. VialTracker runs this math for every vial you log and keeps it with the vial's history.
Safety flags
It is not approved, so there is no legal source. Vials sold online as research chemicals are unapproved, not legal for human use, and may not contain what the label says.
Side effects seen in trials. Nausea, vomiting, diarrhea, and constipation were common, as with other drugs in this class. Increases in heart rate were also reported.
Strength mix-ups. Gray-market vials come in many strengths. Unit and milliliter confusion has caused dosing errors with similar compounded drugs.
FAQ
When will retatrutide be approved?
Lilly plans to file in early 2027. FDA review usually takes about 10 to 12 months, so late 2027 or 2028 at the earliest, if approved.
Can a compounding pharmacy make retatrutide?
No. It is not an approved drug and not eligible for compounding.
Is retatrutide the same as tirzepatide?
No. Both act on GIP and GLP-1, but retatrutide also acts on the glucagon receptor.
Does VialTracker tell me what to take?
No. VialTracker organizes the information you enter and runs the math. It does not recommend doses, products, or protocols.