Retatrutide (LY3437943): Evidence, Side Effects, and Regulatory Status (2026)
Retatrutide (LY3437943) is Investigational (Phase 3). Evidence grade: preliminary. This page is clinically reviewed.
TL;DR / Quick Facts
Retatrutide (LY3437943) is Retatrutide is an investigational triple agonist at GIP, GLP-1, and glucagon receptors. Phase 2 data showed mean weight loss of ~24% at 48 weeks, exceeding both semaglutide and tirzepatide. Phase 3 trials ongoing in 2026. FDA status: Investigational (Phase 3). Typical use cases: weight loss, longevity. Evidence grade: preliminary. Dosing is not established (no FDA-approved protocol). Common side effects: see below. Medriva editorial stance: this compound has limited human evidence; consult a licensed clinician.
What it is
Retatrutide (LY3437943) is a member of the Triple agonist (GIP/GLP-1/glucagon) class. Triple agonism at GIP, GLP-1, and glucagon receptors. The glucagon component increases energy expenditure and may explain the additional weight loss vs dual agonists.
What the evidence says
Evidence for Retatrutide (LY3437943) is preliminary. The bulk of the evidence is from pre-clinical models and small or uncontrolled human studies. Well-controlled phase 3 trials are limited or absent.
[Detailed evidence breakdown in the corresponding claim or pillar pages is linked at the bottom of this page.]
What it's used for
Commonly discussed uses of Retatrutide (LY3437943):
- Weight Loss — preliminary evidence.
- Additional uses listed in the linked use-case hubs; evidence varies by indication.
For the full list, see the linked use-case hubs below.
Dosing is unestablished
No FDA-approved dosing protocol exists for Retatrutide. Published research and clinic-marketed protocols are not interchangeable with medical guidance. Medriva does not publish dosing instructions for research-use or non-approved compounds. Review quality controls with a licensed clinician and use the vendor evaluation framework and COA explainer before considering any source.
Side effects and risks
- Common: Side effects vary by compound and indication; review the approved label or profile-specific safety data with a clinician.
- Serious: Seek urgent care for severe allergic symptoms, chest pain, severe abdominal pain, persistent vomiting, or other severe reactions.
- Long-term unknowns: For non-approved or research-use compounds, long-term human safety data may be limited.
Regulatory status
- FDA-approved use(s): None. Investigational; not yet FDA-approved. Some telehealth and compounding channels market 'research' retatrutide; this is not for human use.
- Compounded availability: see 503A vs 503B explainer
- Research-use-only (RUO) availability: yes
- Banned in sport: see WADA & sports explainer
Cost and access
Retatrutide (LY3437943) is available primarily via telehealth platforms and 503A compounding pharmacies. For pricing, see our cost pages or the GLP-1 price/supply tracker where applicable.
Who it might be appropriate for
Adults with a relevant diagnosed condition or clinical goal, under the supervision of a licensed clinician, who have no contraindications. Retatrutide (LY3437943) is not for self-experimentation.
Who should not use it
Contraindications vary by compound, indication, pregnancy status, comorbidities, and current medications. For the full list, see the contraindications checklist and discuss with your clinician.
Medriva editorial stance
We describe the literature. We do not promote Retatrutide (LY3437943) as a cure, treatment, or performance enhancer. We do not recommend it for self-experimentation. We do recommend that readers (a) understand the evidence grade (preliminary), (b) understand the regulatory status (Investigational (Phase 3)), and (c) discuss with a licensed clinician before acting.
How to talk to a clinician
See our guide on how to talk to a clinician for a templated conversation.
Frequently Asked Questions
Is Retatrutide (LY3437943) FDA-approved?
Investigational (Phase 3). Compounded and RUO versions are not FDA-approved as finished products.
Does Retatrutide (LY3437943) work for weight loss?
Evidence is preliminary. See the linked use-case hub for the full breakdown.
What are the side effects?
See the side effects section above. Discuss with your clinician.
How much does Retatrutide (LY3437943) cost?
See the cost pages or the GLP-1 price/supply tracker where applicable.
Can I buy Retatrutide (LY3437943) online?
Only via prescription from a 503A compounding pharmacy or a licensed telehealth platform. Medriva does not sell peptides and does not endorse RUO vendors.
Author + Clinical reviewer
Author: Sara Iqbal, MS Clinical reviewer: Jonathan Reeves, MD Last reviewed: 2026-06-05
Next steps
- Review the evidence grade and regulatory status before making decisions about Retatrutide.
- Bring this page to a licensed clinician if you are discussing benefits, risks, or alternatives.
- Subscribe to the Medriva Peptide Brief for evidence and regulatory updates.
Related use-case hubs
Related comparisons
Related guides
Editorial process
This page follows the Medriva Editorial Policy and the Clinical Review Methodology. Page last reviewed: 2026-06-05. Author: Sara Iqbal, MS. Clinical reviewer: Jonathan Reeves, MD.
Current source updates
For new regulator actions, compounding-policy changes, warning letters, shortage updates, and sports-rule changes, review the Peptide Tracker before relying on older summaries.
