Side-by-side evidence
Outcomes where both peptides have published data. Each cell carries two grades: clinical evidence (human-RCT depth for this specific outcome) and community evidence (real-world adoption). How we grade evidence.
| Outcome | Retatrutide | Semaglutide |
|---|---|---|
| Body weight reduction | Clinical:Moderate Community:Strong ~24.2% body weight reduction at 48 weeks (Phase 2 obesity trial, 12 mg arm, Jastreboff 2023). | Clinical:Strong Community:Strong ~14.9% body weight reduction at 68 weeks (Phase 3 STEP 1, 2.4 mg weekly, Wilding 2021). |
| Glycemic control (HbA1c) | Clinical:Moderate Community:Strong Up to ~2.16-point HbA1c reduction in Phase 2 T2D trial (Rosenstock 2023); Phase 3 glycemic data pending. | Clinical:Strong Community:Strong FDA-approved for T2D; HbA1c reductions ~1.4-1.8 points across SUSTAIN program. |
| Cardiovascular outcomes | Clinical:Preliminary Community:Moderate Phase 3 CV outcomes data not yet published; glucagon-receptor arm warrants specific monitoring. | Clinical:Strong Community:Strong SUSTAIN-6 documented MACE reduction in T2D; SELECT documented MACE reduction in obesity without diabetes. |
| Mechanism breadth | Clinical:Moderate Community:Strong Triple agonist (GLP-1 + GIP + glucagon); adds energy-expenditure pathway beyond appetite suppression. | Clinical:Strong Community:Strong Single GLP-1 agonist; weight loss driven primarily by reduced caloric intake. |
| Regulatory status | Clinical:Preliminary Community:Strong Phase 3 ongoing; not FDA-approved for any indication. | Clinical:Strong Community:Strong FDA-approved for type 2 diabetes and chronic weight management. |
What This Comparison Covers
Retatrutide and semaglutide sit on opposite ends of the GLP-1-class evolution.
Research-context information only. Retatrutide is an investigational drug not approved by the FDA. Semaglutide is the active ingredient in FDA-approved products for type 2 diabetes and chronic weight management; research-peptide and compounded forms are not FDA-approved and are sold for research purposes only. Protocols, doses, and reactions reported below come from published clinical trials and self-reported community sources. This article reports what has been documented, not what should be done. Possession or use of investigational drugs outside an authorized clinical trial may be illegal in your jurisdiction. Consult a licensed physician for personal medical decisions. Semaglutide is the first-generation single-receptor agonist whose Phase 3 data drove FDA approvals for type 2 diabetes and chronic weight management. Retatrutide is the third-generation triple-receptor agonist that hit the highest weight-loss numbers reported in any obesity trial to date — and remains investigational.
This article compares what trials have documented across mechanism, weight-loss outcomes, glycemic effects, cardiovascular outcomes, side-effect profile, cost, and regulatory status. Community-reported behavior around upgrading from semaglutide to retatrutide is covered separately and labeled as such.
Quick Verdict
Trial-reported peak weight loss: retatrutide ahead by roughly 9 percentage points on cross-trial data (24.2% vs 14.9%), though trial durations and dose ceilings differ.
Regulatory status: semaglutide is FDA-approved for type 2 diabetes and chronic weight management. Retatrutide is investigational and Phase 3 trials are ongoing as of 2026.
Cardiovascular outcomes: semaglutide has Phase 3 cardiovascular outcomes data from SUSTAIN-6 and SELECT. Retatrutide's Phase 3 cardiovascular outcomes data is not yet published.
Mechanism: retatrutide adds GIP and glucagon receptor activation on top of the GLP-1 receptor that semaglutide targets in isolation.
Mechanism Comparison
Semaglutide — single GLP-1 receptor agonist
Semaglutide activates one pathway:
- GLP-1 receptor — slows gastric emptying, increases satiety, enhances glucose-dependent insulin secretion, and acts on central appetite circuits.
The single-receptor mechanism produces the appetite-suppression and glycemic effects responsible for STEP 1's 14.9% weight loss and the SUSTAIN/SELECT cardiovascular benefit. It does not directly activate fat-burning or energy-expenditure pathways — weight loss is driven primarily by reduced caloric intake.
Retatrutide — triple GLP-1 + GIP + glucagon receptor agonist
Retatrutide activates three pathways simultaneously:
- GLP-1 receptor — same appetite, satiety, and insulin effects as semaglutide.
- GIP receptor — additional insulin secretion enhancement and improvements in fat metabolism documented in GIP-class research.
- Glucagon receptor — increases resting energy expenditure and promotes hepatic lipolysis, a pathway not directly engaged by single or dual agonists.
The glucagon difference. GLP-1 single agonists drive weight loss almost entirely through reduced intake. Glucagon receptor activation contributes a separate energy-out lever, which trial researchers describe as a likely mechanism behind the higher peak weight-loss number in Phase 2 (Jastreboff 2023, NEJM).
Weight Loss Head-to-Head
No head-to-head trial has been published. The numbers below are cross-trial — different populations, different durations, different dose ceilings.
Retatrutide Phase 2 Results
The Phase 2 retatrutide obesity trial enrolled 338 adults with obesity (BMI ≥30) without diabetes (Jastreboff 2023, NEJM):
- 1 mg weekly: 8.7% body weight reduction at 48 weeks
- 4 mg weekly: 17.1% body weight reduction at 48 weeks
- 8 mg weekly: 22.8% body weight reduction at 48 weeks
- 12 mg weekly: 24.2% body weight reduction at 48 weeks
- Responder rate at 12 mg: approximately 83% of subjects achieved ≥15% body weight reduction
A Phase 2 diabetes trial reported HbA1c reductions of up to 2.16 percentage points at 36 weeks (Rosenstock 2023, Lancet).
Semaglutide Phase 3 Results (STEP 1)
The Phase 3 STEP 1 trial enrolled 1,961 adults with overweight or obesity (BMI ≥27 with comorbidities or BMI ≥30) without diabetes (Wilding 2021, NEJM):
- 2.4 mg weekly: 14.9% body weight reduction at 68 weeks
- Placebo arm: 2.4% body weight reduction at 68 weeks
- Responder rates: 86% of subjects on semaglutide achieved ≥5% weight reduction; 50.5% achieved ≥15%
Cross-Trial Snapshot
| Metric | Retatrutide (Phase 2, 12 mg) | Semaglutide (STEP 1, 2.4 mg) |
|---|---|---|
| Peak body weight reduction reported | 24.2% | 14.9% |
| Trial duration | 48 weeks | 68 weeks |
| ≥15% responder rate reported | ~83% | ~50.5% |
| Trial phase | Phase 2 | Phase 3 (pivotal) |
| FDA status | Investigational | Approved for chronic weight management |
Important caveat: retatrutide's Phase 3 trial data is not yet fully published. The 24.2% number is a Phase 2 result from a smaller, shorter trial than STEP 1. The percentage-point gap may narrow once Phase 3 retatrutide data is in.
Glycemic and Cardiovascular Outcomes
Glycemic control
Semaglutide is FDA-approved for type 2 diabetes; HbA1c reductions of approximately 1.4 to 1.8 percentage points were documented across the SUSTAIN program. Retatrutide's Phase 2 diabetes trial reported HbA1c reductions of up to 2.16 percentage points at 36 weeks (Rosenstock 2023, Lancet) — directionally larger, but on Phase 2 data without the multi-year safety record SUSTAIN provides.
Cardiovascular outcomes
This is the largest evidence gap between the two compounds.
- Semaglutide: SUSTAIN-6 reported a 26% relative reduction in major adverse cardiovascular events in adults with type 2 diabetes (Marso 2016, NEJM). SELECT reported a 20% relative reduction in MACE in adults with overweight or obesity and preexisting cardiovascular disease, without diabetes (Lincoff 2023, NEJM).
- Retatrutide: Phase 3 cardiovascular outcomes data is not yet published. The TRIUMPH program is ongoing.
The cardiovascular evidence gap matters in two directions: it is a hard advantage for semaglutide on documented benefit, and an unknown for retatrutide that the glucagon-receptor arm makes worth watching specifically (glucagon-agonist effects on heart rate and metabolic rate are documented but the long-term MACE signal is open).
Side Effect Profile
Both compounds share a GLP-1-class GI profile. Retatrutide adds glucagon-receptor-specific effects.
| Reported effect | Retatrutide (Phase 2) | Semaglutide (STEP 1) |
|---|---|---|
| Nausea | ~25-35% (dose-dependent) | ~44% |
| Diarrhea | ~20-25% | ~30% |
| Vomiting | ~15-20% | ~24% |
| Constipation | ~15-20% | ~24% |
| Discontinuation due to adverse events | Higher on top doses | ~7.0% (semaglutide) vs 3.1% (placebo) |
| Heart rate elevation | Mild, dose-dependent (glucagon arm) | Modest, GLP-1-class effect |
Glucagon-receptor-specific effects (retatrutide only). Phase 2 trial data documented mild dose-dependent heart rate elevation and a thermogenesis-related signal that may translate to mild sweating in higher-dose subjects. These are not documented at meaningful rates in semaglutide trials.
For full side-effect breakdowns see Retatrutide Side Effects and Semaglutide Side Effects.
Dosing Differences
Trial doses for the two compounds operate on different scales.
- Semaglutide (chronic weight management trial protocol): titrated from 0.25 mg to 2.4 mg subcutaneously once weekly over approximately 16 weeks.
- Retatrutide (Phase 2 obesity trial protocol): titrated from 2 mg to 12 mg subcutaneously once weekly over approximately 16 weeks. Self-reported community protocols cluster well below the 12 mg trial ceiling, commonly at 1.5-4 mg weekly split across two or three injections per week.
The trial-protocol weekly mg load for retatrutide is roughly 5x semaglutide at the respective ceilings. Reconstitution math, vial sizing, and injection-volume math differ substantially as a result — covered in the Retatrutide Reconstitution Guide and Semaglutide Reconstitution Guide.
Cost Comparison
For current research-vendor pricing across both compounds, see Retatrutide Cost & Vial Math and Semaglutide Cost & Vial Math.
Trial subjects in the FDA-approved-product arms of STEP and SUSTAIN received semaglutide as a finished pharmaceutical product; the commercial branded product is sold at a substantially higher list price than research-grade compounded or peptide-vendor semaglutide. Retatrutide has no FDA-approved finished-product equivalent — all retatrutide available outside authorized clinical trials is research-grade.
For live vendor pricing across both, see the Live Prices page.
