Three-Way Comparison
Retatrutide vs Tirzepatide vs Semaglutide: The Complete 2026 Comparison
The retatrutide vs tirzepatide vs semaglutide question comes down to how many hormone receptors each drug hits and whether it is actually available. Semaglutide is a single GLP-1 agonist and lost 14.9% of body weight in its STEP 1 trial. Tirzepatide is a dual GLP-1/GIP agonist and lost 20.9% in SURMOUNT-1. Retatrutide is a triple GLP-1/GIP/glucagon agonist and lost 24.2% in a Phase 2 trial, but it is investigational and not FDA-approved. The table below sets all three side by side so you can compare the figures in seconds.
Key Takeaways
- One, two, three receptors: semaglutide targets GLP-1 only, tirzepatide adds GIP, retatrutide adds glucagon on top of that.
- Trial weight loss rises with each added target: 14.9% (semaglutide, STEP 1), 20.9% (tirzepatide, SURMOUNT-1), 24.2% (retatrutide, Phase 2). Different trials, not a head-to-head ranking.
- Availability is the practical divide: semaglutide and tirzepatide are FDA-approved; retatrutide is investigational with Phase 3 trials still running as of 2026.
- SURMOUNT-5 is the only direct comparison: tirzepatide 15mg reached 20.2% versus semaglutide 2.4mg at 13.7% over 72 weeks in people with obesity and no type 2 diabetes.
- Side effects are GI-dominant for all three. Nausea is the most common: 44 percent on Wegovy 2.4mg and 25 to 29 percent on Zepbound 5mg to 15mg (per their labels), and 28.6 to 42.4 percent on retatrutide 4mg to 12mg in Phase 3 TRIUMPH-1 (Jastreboff et al., NEJM 2026). These come from separate trials, not a head-to-head comparison.
14.9%
Semaglutide, STEP 1, 68 weeks, 2.4mg
20.9%
Tirzepatide, SURMOUNT-1, 72 weeks, 15mg
24.2%
Retatrutide, Phase 2, 48 weeks, 12mg
1
Head-to-head trial among the three (SURMOUNT-5)
Retatrutide vs Tirzepatide vs Semaglutide: Quick Comparison Table
This is the fastest way to see how the three medications line up. Each row covers a dimension people ask about most: mechanism, receptor count, FDA status, the headline trial weight loss figure, half-life, dosing, brand names, and availability.
| Feature | Semaglutide | Tirzepatide | Retatrutide |
|---|---|---|---|
| Mechanism | GLP-1 agonist (single) | GLP-1/GIP agonist (dual) | GLP-1/GIP/glucagon agonist (triple) |
| Receptor Targets | 1 | 2 | 3 |
| FDA Status | Approved | Approved | Investigational (Phase 3) |
| Max Trial Weight Loss | 14.9% | 20.9% | 24.2% |
| Trial Anchor | STEP 1, 2.4mg, 68 wks | SURMOUNT-1, 15mg, 72 wks | Phase 2, 12mg, 48 wks |
| Half-Life | ~7 days | ~5 days | ~6 days |
| Starting Dose | 0.25mg weekly | 2.5mg weekly | 2mg weekly |
| Max Dose | 2.4mg maintenance, 7.2mg max (obesity) | 15mg | 12mg |
| Brand Names | Wegovy, Ozempic, Rybelsus | Mounjaro, Zepbound | None yet |
| Availability | Pharmacy, prescription | Pharmacy, prescription | US: clinical trial or Lilly's narrow expanded access program (NCT07629401) only |
Retatrutide is not FDA-approved
In the US, the routes available today are a clinical trial or Lilly's expanded access program (ClinicalTrials.gov NCT07629401), which a doctor must request, for adults with a BMI of 35 or more whose obesity has not responded to the highest available dose of current weight-loss treatment, who have two or more serious obesity-related complications, and who cannot join a trial. Lilly provides the product at no cost, but the doctor must apply to the FDA as sponsor of a patient-specific investigational new drug (IND) application and obtain IRB approval (Lilly Medical). The figures above are Phase 2 data, and Phase 3 results (reported since December 2025) may differ. It cannot be prescribed or bought through a pharmacy or telehealth provider in 2026.
How to Read This Table
These weight loss figures come from three different trials with different participant populations, durations, and trial designs. No single study has tested all three medications head to head. The closest available evidence is SURMOUNT-5, the only direct randomized comparison between two of the three (tirzepatide versus semaglutide in obesity). Read the percentages as separate results, not as a finish-line ranking.
Quick Answer
In published trials, retatrutide produced the most weight loss (24.2% over 48 weeks, Phase 2), followed by tirzepatide (20.9% over 72 weeks, SURMOUNT-1) and semaglutide (14.9% over 68 weeks, STEP 1). Those figures come from three separate trials with different designs and populations, so they are not directly comparable. Semaglutide and tirzepatide are FDA-approved and prescribable now; retatrutide is investigational and in the US available only through a clinical trial or Lilly's narrow expanded access program (NCT07629401). The only direct head-to-head study among the three is SURMOUNT-5, which compared tirzepatide and semaglutide.
Model Any of the Three on One Calculator
Use the free GLP3Planner calculators to map dose schedules and half-life decay for retatrutide, tirzepatide, or semaglutide.
How Each Drug Works: 1 Receptor, 2 Receptors, 3 Receptors
What separates these three medications is how many gut and metabolic hormone receptors each one activates. Each added target has tracked with more weight loss in trials, along with a different side effect picture. For a deeper breakdown of the receptor classes, see the full GLP-3 vs GLP-1 comparison chart.
Semaglutide: the GLP-1 Pioneer (1 Receptor)
Semaglutide is a GLP-1 receptor agonist. Activating GLP-1 suppresses appetite, slows gastric emptying so you feel full longer, and stimulates glucose-dependent insulin secretion. This single mechanism delivered 14.9% mean body weight loss at 68 weeks on 2.4mg in the STEP 1 trial (Wilding et al., NEJM 2021). It is the most studied of the three and has the longest real-world track record.
Tirzepatide: Dual-Agonist Advantage (2 Receptors)
Tirzepatide keeps the GLP-1 action and adds GIP (glucose-dependent insulinotropic polypeptide) agonism. The GIP component contributes to insulin sensitivity and fat metabolism, and the combined effect produced 20.9% mean body weight loss at 72 weeks on 15mg in SURMOUNT-1 (Jastreboff et al., NEJM 2022). Adding the second receptor target tracked with more weight loss than the single-agonist class in trials.
Retatrutide: Triple-Agonist With Glucagon (3 Receptors)
Retatrutide (LY3437943, developed by Eli Lilly) keeps GLP-1 and GIP action and adds a glucagon receptor target. Glucagon agonism increases energy expenditure and accelerates fat metabolism, which is the mechanistic rationale behind its high Phase 2 weight loss of 24.2% at 48 weeks on 12mg (Jastreboff et al., NEJM 2023). The pharmacokinetic and mechanism work behind the molecule was first detailed by Coskun et al. in Cell Metabolism (2022) [7]. Retatrutide remains investigational and is not approved for any use.
Weight Loss Results: What the Trials Showed
Read these as separate trial results, not a head-to-head ranking
STEP 1, SURMOUNT-1, and the retatrutide Phase 2 trial enrolled different populations, ran for different durations, and used different designs. A higher percentage in one trial does not prove one drug outperforms another in the same patient. The one direct randomized comparison among the three is SURMOUNT-5, covered below.
Semaglutide Weight Loss Data (STEP 1)
In the STEP 1 trial, semaglutide 2.4mg produced 14.9% mean body weight loss at 68 weeks (Wilding et al., NEJM 2021). Semaglutide is also the only one of the three with a dedicated cardiovascular outcomes indication: the SELECT trial, published in 2023, showed it reduced the risk of cardiovascular death, heart attack, and stroke in adults with established cardiovascular disease; the FDA granted that cardiovascular risk-reduction indication in 2024, making it the first weight-loss drug to earn one.
Tirzepatide Weight Loss Data (SURMOUNT-1 and SURMOUNT-5)
Tirzepatide 15mg produced 20.9% mean body weight loss at 72 weeks in SURMOUNT-1 (Jastreboff et al., NEJM 2022). SURMOUNT-5 went further and ran the only direct head-to-head randomized trial among any two of the three: in adults with obesity and no type 2 diabetes, tirzepatide 15mg reached 20.2% versus semaglutide 2.4mg at 13.7% over 72 weeks. SURMOUNT-5 was funded by Eli Lilly, the maker of tirzepatide, and independent replication is still pending. For the full breakdown of that pairing, see our tirzepatide vs semaglutide in-depth comparison.
Retatrutide Weight Loss Data (Phase 2, NEJM 2023)
Retatrutide 12mg produced 24.2% mean body weight loss at 48 weeks in its Phase 2 trial (Jastreboff et al., NEJM 2023). These are Phase 2 results, and Phase 3 trials reported since December 2025 may show different numbers. A 2025 network meta-analysis of clinical trials (Salhab et al., Journal of the Endocrine Society) supported retatrutide's weight loss advantage over tirzepatide, and estimated a higher adverse-event risk versus placebo for retatrutide (RR 4.10) than for tirzepatide (RR 2.78), without testing the two directly. That meta-analysis used indirect modeled estimates, not a direct trial, so the headline figure to rely on is the 24.2% Phase 2 result. For the two-drug deep dive, see the retatrutide vs tirzepatide comparison.
Side Effects: What to Expect From Each
All three medications share a gastrointestinal-dominant side effect profile: nausea, diarrhea, vomiting, and constipation. The differences are in intensity and reported rates, not the type of effect. None of the figures below are framed as "safer than" another drug, because they come from separate trials.
Shared GI Profile Across All Three
GLP-1 agonism slows gastric emptying, which is why nausea is the most common complaint across the whole class. Symptoms typically peak in the first 4 to 8 weeks and ease as the dose is titrated slowly. Eating smaller meals, avoiding high-fat foods during titration, and staying hydrated are the standard strategies.
Semaglutide Side Effects
Semaglutide's side effect profile is the best characterized of the three given its longer market history. STEP 1 reported the same GI-dominant pattern, mostly mild to moderate and dose-dependent. Patient-community discussion of "Ozempic face" or muscle loss falls outside the scope of the clinical weight loss claims described here.
Tirzepatide Side Effects
In the Zepbound prescribing information (Table 1, pooled SURMOUNT-1 and SURMOUNT-2, adults with obesity or overweight, about a quarter of them with type 2 diabetes), gastrointestinal adverse event rates across the 5mg to 15mg doses were 25 to 29 percent for nausea, 19 to 23 percent for diarrhea, 8 to 13 percent for vomiting, and 11 to 17 percent for constipation, versus 8, 8, 2, and 5 percent on placebo. The 5mg column comes from SURMOUNT-1 only; the 10mg and 15mg columns also include SURMOUNT-2 (adults with type 2 diabetes), so the columns are not a clean dose comparison. Slow titration is still standard to limit GI effects.
Retatrutide Side Effects
Retatrutide has no FDA label, so its rates come from trials. In Phase 3 TRIUMPH-1 (Jastreboff et al., NEJM 2026; adults with obesity or overweight, without diabetes), nausea affected 28.6 to 42.4 percent across 4mg to 12mg versus 14.8 percent on placebo, diarrhea 25.2 to 34.1 percent, constipation 23.8 to 26.1 percent, and vomiting 10.6 to 25.3 percent. Discontinuation due to adverse events was 4.1 to 11.2 percent versus 4.6 percent on placebo. In the earlier Phase 2 trial, nausea reached 45 percent at 12mg. These figures come from separate trials with different populations and durations from the semaglutide and tirzepatide studies, and no head-to-head retatrutide trial has reported yet (TRIUMPH-5, retatrutide vs tirzepatide, is still running). An indirect 2025 network meta-analysis (Salhab et al., conference abstract) estimated adverse-event risk versus placebo at RR 4.10 for retatrutide and 2.78 for tirzepatide; it did not test the two directly.
A key safety consideration for retatrutide
Retatrutide's gastrointestinal adverse event rates matter, particularly because its long-term safety data is still accumulating. You cannot call an investigational drug "safe" before its trial program completes.
FDA Approval Status and Availability
This is what decides whether any of these drugs is actually an option for you right now. Two are approved and prescribable; one is not.
Semaglutide: Fully FDA-Approved
Semaglutide is approved as Wegovy for obesity, Ozempic for type 2 diabetes, and, in oral form, the Ozempic pill for type 2 diabetes (1.5/4/9mg, which reformulated and renamed Rybelsus in 2026) and the Wegovy pill for weight management (25mg, approved December 2025). Wegovy also carries a cardiovascular risk reduction indication (from the SELECT trial, 2024) and a pediatric weight management indication for ages 12 and older (2023). It is available at pharmacies with a prescription.
Tirzepatide: Fully FDA-Approved
Tirzepatide is approved as Mounjaro for type 2 diabetes (2022) and Zepbound for obesity (2023). Zepbound also became the first drug approved for moderate-to-severe obstructive sleep apnea in adults with obesity (2024). It is available at pharmacies, and Eli Lilly's LillyDirect vial program offers a cash-pay pathway. See our tirzepatide hub for the full brand guide.
Retatrutide: Investigational Only
Retatrutide has reported Phase 3 results but, as of 2026, it is not FDA-approved, is not available at pharmacies, and is not offered through telehealth; Lilly plans to file with the FDA in Q1 2027. In the US, the routes available today are a clinical trial or Lilly's narrow expanded access program (NCT07629401). Research-peptide sourcing is a separate channel that carries significant quality and legal risk and should not be confused with an investigational drug trial. See our retatrutide hub for the current status, and the compounded retatrutide article for compounding context.
Which Class Is Right for You? A Decision Framework
No single drug is the best choice for everyone, and nothing here is a personalized recommendation. These five questions are the ones a clinician would weigh with you. Use them to frame a conversation, not to self-prescribe.
1. Do you need an FDA-approved option now?
If yes, only semaglutide or tirzepatide qualify. Retatrutide is not an option outside a clinical trial.
2. Do you have type 2 diabetes?
All three have type 2 diabetes data. Tirzepatide (Mounjaro) has the most extensive type 2 diabetes trial portfolio through the SURPASS program.
3. Do you have a cardiovascular disease history?
Semaglutide (Wegovy) is the only one with a dedicated cardiovascular outcomes indication, based on the SELECT trial.
4. Do you have sleep apnea?
Tirzepatide (Zepbound) is the only one with an FDA-approved indication for moderate-to-severe obstructive sleep apnea in adults with obesity.
5. Are you interested in future options?
Most retatrutide Phase 3 trials are no longer enrolling; check ClinicalTrials.gov for open studies and discuss it with your physician. If you are currently on semaglutide and considering a change, our switching guide covers what that transition involves.
Cost and Access Overview
This is a directional snapshot, not a full cost guide. Prices change and depend heavily on insurance, savings programs, and pharmacy. For full breakdowns, see the retatrutide cost and tirzepatide cost articles.
| Drug | Approximate Cash Price | Insurance Coverage |
|---|---|---|
| Semaglutide (Wegovy) | ~$1,300+/month list; Novo Nordisk savings program available | Covered for obesity by some commercial plans |
| Tirzepatide (Zepbound) | $299 to $499/month via LillyDirect vials; ~$1,086/month pen list | Covered for obesity with prior authorization |
| Retatrutide | Not commercially available | Not applicable; in the US, clinical trial or narrow expanded access only |
The Bottom Line
Semaglutide is the proven, most-studied option and the only one with a cardiovascular outcomes indication. Tirzepatide showed greater weight loss than semaglutide in the only direct head-to-head trial among the three (SURMOUNT-5), and it adds a sleep apnea indication. Retatrutide produced the highest weight loss in its Phase 2 trial but is not FDA-approved and carried a higher adverse event rate.
The right choice depends on your medical history, goals, insurance coverage, and access. Two of the three can be prescribed today; one cannot be obtained outside a clinical trial. Take the comparison table and these trial figures into a conversation with a clinician who knows your full history, rather than treating any single percentage as the answer.
Video: A Pharmacist Compares the Big Three
A pharmacist-credentialed channel walks through the same three-way comparison using Phase 2 trial data, including mechanism, speed of weight loss, and side effects.
Frequently Asked Questions
Which is stronger for weight loss: retatrutide, tirzepatide, or semaglutide?
In Phase 2 trials, retatrutide showed the highest weight loss at 24.2% over 48 weeks. Tirzepatide showed 20.9% at 72 weeks in SURMOUNT-1. Semaglutide showed 14.9% at 68 weeks in STEP 1. These come from separate trials with different designs; no three-way head-to-head trial has been conducted.
Is retatrutide available to buy or prescribe in 2026?
No. Retatrutide remains investigational in 2026: Phase 3 results have been reported, and Lilly plans to file with the FDA in Q1 2027. It is not FDA-approved, cannot be prescribed, and is not commercially available. In the US, lawful access is limited to a clinical trial or Lilly's narrow expanded access program (NCT07629401). Most retatrutide Phase 3 trials are no longer enrolling; check ClinicalTrials.gov for open studies.
What is the difference between a single, dual, and triple agonist?
Semaglutide targets one receptor (GLP-1), suppressing appetite and slowing digestion. Tirzepatide targets two (GLP-1 and GIP), adding insulin-sensitivity benefits. Retatrutide targets three (GLP-1, GIP, and glucagon), also increasing energy expenditure. More targets tracked with greater weight loss in trials, but also with more adverse events.
Should I switch from tirzepatide to retatrutide?
In the US, retatrutide is available only through a clinical trial or Lilly's narrow expanded access program, so switching is not a practical option in 2026. If tirzepatide is working well, there is no approved alternative to move to. Discuss trial participation with your physician if you are interested in retatrutide.
Which weight loss drug has the fewest side effects?
All three cause primarily GI side effects. Semaglutide has the most long-term real-world data; the Wegovy label reports nausea in 44 percent on 2.4mg versus 16 percent on placebo. The Zepbound label reports nausea in 25 to 29 percent across 5mg to 15mg tirzepatide versus 8 percent on placebo. Retatrutide has no label: in its Phase 3 TRIUMPH-1 trial (Jastreboff et al., NEJM 2026; adults without diabetes), nausea affected 28.6 to 42.4 percent across 4mg to 12mg versus 14.8 percent on placebo. These come from separate trials with different populations and durations, so they cannot rank the three drugs. Effects are dose-dependent for all three.
Does tirzepatide work better than semaglutide?
In the SURMOUNT-5 head-to-head trial (obesity, no type 2 diabetes), tirzepatide 15mg produced 20.2% weight loss versus semaglutide 2.4mg at 13.7% over 72 weeks. This is the only direct randomized comparison of the two. The trial was Lilly-funded, and independent replication is pending.
What is the half-life of each drug and why does it matter?
Semaglutide has the longest half-life at approximately 7 days, tirzepatide approximately 5 days, and retatrutide approximately 6 days. A longer half-life means more stable blood levels between weekly injections. All three are dosed once weekly, and the half-life differences have limited practical impact at standard schedules.
Is retatrutide the same as a GLP-3?
Retatrutide targets three receptors (GLP-1, GIP, and glucagon) and is sometimes informally called a "GLP-3" or triple agonist. That is colloquial shorthand, not an official drug class. Its formal designation is a triple hormone receptor agonist, molecule ID LY3437943, developed by Eli Lilly.
Which is better, Mounjaro or retatrutide?
Mounjaro (tirzepatide) is FDA-approved for type 2 diabetes and can be prescribed now. Retatrutide is investigational and, in the US, available only through a clinical trial or Lilly's narrow expanded access program. In Phase 2 data, retatrutide produced higher weight loss but with more adverse events. A practical comparison is premature until retatrutide is approved.
Which drug is best for someone with type 2 diabetes?
All three have type 2 diabetes efficacy data. Tirzepatide (Mounjaro) has the most extensive type 2 diabetes trial portfolio across the SURPASS series. Semaglutide (Ozempic) is also well-established. Retatrutide's diabetes data now includes the Phase 3 TRIUMPH-2 trial in adults with obesity or overweight and type 2 diabetes (The Lancet, 2026), but it is not approved for any use. Prescribers weigh HbA1c, weight goals, cardiovascular history, and coverage.
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References
- Jastreboff AM, Kaplan LM, Frias JP, et al. Triple-Hormone-Receptor Agonist Retatrutide for Obesity: A Phase 2 Trial. N Engl J Med. 2023;389(6):514-526. DOI: 10.1056/NEJMoa2301972.
- Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). N Engl J Med. 2022;387(3):205-216. DOI: 10.1056/NEJMoa2206038.
- Wilding JPH, Batterham RL, Calanna S, et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1). N Engl J Med. 2021;384(11):989-1002. DOI: 10.1056/NEJMoa2032183.
- Aronne LJ, Horn DB, le Roux CW, et al. Tirzepatide as Compared with Semaglutide for the Treatment of Obesity (SURMOUNT-5). N Engl J Med. 2025;393:26-36. DOI: 10.1056/NEJMoa2416394.
- Salhab A, Maraqah H, Habes Y, Abusabha M, Ayesh H. Comparative Efficacy and Safety of Tirzepatide vs Retatrutide in Weight Loss: A Network Meta-Analysis of Clinical Trials. J Endocr Soc. 2025;9(Suppl 1):bvaf149.169. DOI: 10.1210/jendso/bvaf149.169.
- Lincoff AM, Brown-Frandsen K, Colhoun HM, et al. Semaglutide and Cardiovascular Outcomes in Obesity without Diabetes (SELECT). N Engl J Med. 2023;389:2221-2232. DOI: 10.1056/NEJMoa2307563.
- Coskun T, Sloop KW, Loghin C, et al. LY3437943, a novel triple glucagon, GIP, and GLP-1 receptor agonist for glycemic control and weight loss: From discovery to clinical proof of concept. Cell Metab. 2022;34(9):1234-1247.e9. DOI: 10.1016/j.cmet.2022.07.013.
- Jastreboff AM, Kaplan LM, Davies MJ, et al. Retatrutide, a Triple Hormone Receptor Agonist, for Treatment of Obesity (TRIUMPH-1). N Engl J Med. Published online September 29, 2026. DOI: 10.1056/NEJMoa2604169.
- Eli Lilly Medical Information. What are the results of retatrutide from TRIUMPH-1 in participants with obesity or overweight without type 2 diabetes? (TRIUMPH-1 adverse-event table, citing the NEJM paper).
- ClinicalTrials.gov. A Study of LY3437943 in Participants Who Have Obesity or Overweight (NCT04881760). Posted results, adverse events.
- ZEPBOUND (tirzepatide) prescribing information, Section 6.1, Table 1. Eli Lilly and Company; DailyMed.
- WEGOVY (semaglutide) prescribing information, Section 6.1, Table 3. Novo Nordisk; DailyMed.
Medical Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare provider before starting, changing, or stopping any medication. Individual results vary, and what works for one person may not be appropriate for another. Retatrutide is investigational and is not FDA-approved; the data described here are from clinical trials only and should not be used for self-treatment.
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