Retatrutide vs tirzepatide vs semaglutide, in short: semaglutide (Wegovy, Ozempic) and tirzepatide (Zepbound, Mounjaro) are FDA-approved drugs backed by large phase 3 trials, and tirzepatide beat semaglutide for weight loss in a direct head-to-head trial. Retatrutide is investigational and not approved anywhere. It has published phase 2 and phase 3 data and, since 2026-10-28, a first head-to-head result against semaglutide in type 2 diabetes, but no cardiovascular outcome data yet. Outside clinical trials there is no legal source of it, and the FDA says it cannot be compounded under federal law.
| Item | Retatrutide | Tirzepatide | Semaglutide |
|---|---|---|---|
| US FDA status | Investigational, not approved (FDA) | Approved: Mounjaro (2022), Zepbound (2023) | Approved: Ozempic (2017), Wegovy (2021) |
| Compounding | “Cannot be used in compounding under federal law” (FDA) | FDA proposed 503B bulks exclusion, 2026-04-30 (FDA) | Same 503B exclusion proposal (FDA) |
| WADA 2026 | Prohibited at all times under S0 Non-Approved Substances, which covers any drug without regulatory approval; not named individually (USADA) | Not prohibited; WADA is monitoring GLP-1 use (USADA) | Not prohibited; monitored (USADA) |
| Strongest evidence | Human RCT, phase 3 (n=1,152) | Approved label; phase 3 RCTs | Approved label; outcome RCT (n=17,604) |
| Human trials | Phase 3: NCT05929066, NCT05929079, NCT05882045, NCT05931367 | Head-to-head vs semaglutide: NCT05822830 | SURMOUNT-5 comparator; SELECT outcome trial |
| Last checked | 2026-10-11 | 2026-09-30 | 2026-09-30 |
What changed (October 2026): the retatrutide rows now use phase 3 results (TRIUMPH-1 for weight, the two dedicated sleep apnea trials published on 2026-10-21, TRIUMPH-4 for knee pain), the sport rows no longer contradict each other, and the 2027 WADA List is added.
Key points:
- The only published direct randomized comparison among the three is tirzepatide vs semaglutide: −20.2% vs −13.7% body weight at 72 weeks in 751 adults without diabetes (Human RCT, n=751).
- Retatrutide’s first head-to-head trial, against semaglutide (Ozempic 2 mg, Ozempic’s highest approved dose) in 1,298 adults with type 2 diabetes, reported on 2026-10-28: at 80 weeks HbA1c fell 2.2 points on retatrutide 9 mg and 12 mg versus 1.8, and weight fell 19.5% and 20.9% versus 9.4% (Lilly topline, not yet peer reviewed) [Human RCT, open-label, n=1,298]. As of 2026-10-29, no trial has reported results for retatrutide against tirzepatide.
- Semaglutide is the only one of the three with a completed cardiovascular outcome trial that beat placebo (SELECT, n=17,604).
- In a 2026 US health-records study of 271,685 matched pairs of adults with type 2 diabetes, tirzepatide users had fewer heart attacks, strokes and heart-failure events than semaglutide users (4.6% vs 5.5%) and fewer deaths (0.6% vs 0.9%). It is an observational study, so other differences between the groups may explain part of the gap (Al-Nusair 2026) [Human observational, n=543,370].
- Both approved drugs carry a boxed warning for thyroid C-cell tumors (Wegovy label; Zepbound label). In a phase 3 trial, dysesthesia (abnormal skin sensations) and low blood pressure occurred more often with retatrutide than with placebo (TRIUMPH-2, n=1,152).
Retatrutide vs tirzepatide vs semaglutide at a glance
| Feature | Retatrutide | Tirzepatide | Semaglutide |
|---|---|---|---|
| What it is | Investigational weekly peptide (Lilly) | Approved weekly peptide (Lilly) | Approved peptide, weekly or daily pill (Novo Nordisk) |
| Receptors | GIP + GLP-1 + glucagon (triple) | GIP + GLP-1 (dual) | GLP-1 only |
| Main research focus | Obesity, type 2 diabetes, knee osteoarthritis, sleep apnea, liver fat | Obesity, type 2 diabetes, sleep apnea | Obesity, type 2 diabetes, heart risk, MASH |
| Top weight result, no diabetes | −25.0% at 80 wk (phase 3) | −20.9% at 72 wk | −14.9% at 68 wk |
| US approval | None | Zepbound, Mounjaro | Wegovy, Ozempic |
| WADA | Prohibited at all times (S0, unapproved) | Not prohibited | Not prohibited |
| Routes studied | Subcutaneous, weekly | Subcutaneous, weekly | Subcutaneous weekly; oral daily |
| Outcome trial | Running, est. 2029 | Noninferior to dulaglutide | MACE HR 0.80 vs placebo |
| Main safety concerns | GI effects, heart rate rise, dysesthesia, low blood pressure; long-term unknown | GI effects, pancreatitis, gallbladder disease, thyroid boxed warning | GI effects, pancreatitis, gallbladder disease, heart rate rise, thyroid boxed warning |
Sources for the table: retatrutide phase 2, TRIUMPH-1, TRIUMPH-2 and TRIUMPH-Outcomes; tirzepatide SURMOUNT-1 and SURPASS-CVOT; semaglutide STEP 1 and SELECT; the Wegovy and Zepbound labels. Trial populations differ, so the weight rows are not a head-to-head ranking.
What is retatrutide?
Retatrutide (LY3437943) is an experimental once-weekly peptide from Eli Lilly that activates three hormone receptors: GIP, GLP-1 and glucagon (Jastreboff 2023). Its phase 3 program, TRIUMPH, covers obesity, type 2 diabetes, knee osteoarthritis and obstructive sleep apnea (Giblin 2026, design paper). Three phase 3 trials have peer-reviewed results (TRIUMPH-1; TRIUMPH-2; TRANSCEND-T2D-1). Retatrutide is not approved, and the FDA has warned companies selling it labeled “for research purposes” (FDA).
What is tirzepatide?
Tirzepatide is a once-weekly dual GIP and GLP-1 receptor agonist. It is approved as Mounjaro for type 2 diabetes (2022) and as Zepbound (2023) (Drugs@FDA). Zepbound’s label covers chronic weight management and moderate to severe obstructive sleep apnea in adults with obesity (Approved label). In the EU, Mounjaro has been authorized since September 2022 for type 2 diabetes and weight management (EMA).
What is semaglutide?
Semaglutide is a GLP-1 receptor agonist. It is sold as Ozempic for type 2 diabetes (approved 2017) and as Wegovy for weight management (approved 2021) (Drugs@FDA). Wegovy’s current label also covers lowering the risk of major cardiovascular events in adults with heart disease and overweight or obesity, and noncirrhotic MASH with moderate to advanced liver fibrosis. It now comes as a daily tablet as well as a weekly injectable (Approved label).
How do they work differently?
- Semaglutide: activates only the GLP-1 receptor, which reduces appetite and lowers blood sugar (Approved label).
- Tirzepatide: activates GLP-1 receptors and also receptors for GIP, a second gut hormone (Approved label). The FDA links its sleep apnea benefit to weight reduction (FDA).
- Retatrutide: adds glucagon receptor activation to GIP and GLP-1 activation. Cryo-electron microscopy structures show it binding all three receptors (Lab (in vitro)). In a phase 2a substudy it cut liver fat by up to 82.4% at 24 weeks (Human RCT, n=98). Heart rate rose in a dose-dependent way, peaked at 24 weeks and then declined (Human RCT, n=338).
Evidence head-to-head
| Outcome | Retatrutide | Tirzepatide | Semaglutide |
|---|---|---|---|
| Weight loss, no diabetes | Human RCT, phase 3 (n=2,339): −25.0% at 12 mg vs −3.9% placebo, 80 wk (link) | Human RCT (n=2,539): −20.9% at 15 mg vs −3.1%, 72 wk (link) | Human RCT (n=1,961): −14.9% vs −2.4%, 68 wk (link) |
| Direct comparison | Human RCT, open-label (n=1,298), type 2 diabetes: −19.5% to −20.9% vs −9.4% weight and −2.2 vs −1.8 HbA1c points with Ozempic 2 mg, 80 wk (Lilly topline, link) | Human RCT (n=751): −20.2% vs −13.7% for semaglutide (link) | Comparator in both trials |
| Weight loss, obesity + type 2 diabetes | Human RCT, phase 3 (n=1,152): −18.8% at 12 mg vs −5.1%, 80 wk (link) | Human RCT (n=1,879): 1.9–5.5 kg more than semaglutide 1 mg, 40 wk (link) | Comparator in the same trial |
| HbA1c (blood sugar) | Human RCT, phase 3 (n=537): −1.94 points at 12 mg vs −0.81, 40 wk (link) | Human RCT (n=1,879): −2.01 to −2.30 points (link) | Same trial: −1.86 points at 1 mg |
| Heart attack, stroke, CV death | No data; outcome trial running (NCT06383390) | Human RCT (n=13,299): noninferior to dulaglutide, HR 0.92 (link) | Human RCT (n=17,604): HR 0.80 vs placebo (link) |
| Sleep apnea | Human RCT, 2 phase 3 trials (n=243 and n=448), 80 wk: apnea events −36.1 vs −11.1 per hour on 9 mg without diabetes, −28.4 vs −10.6 on 12 mg with type 2 diabetes (NEJM 2026) | Approved label: 2 RCTs, 469 adults (FDA) | Not an approved indication |
| Liver (MASLD/MASH) | Human RCT, phase 2a (n=98): liver fat −82.4% at 12 mg (link) | Not an approved indication | Approved label (accelerated approval) (FDA) |
| Knee osteoarthritis | Human RCT, phase 3 topline (n=445), 68 wk: WOMAC pain −4.5 / −4.4 vs −2.4 points on 9 / 12 mg (TRIUMPH-4) | Not reviewed here | Not reviewed here |
Two points matter when reading this table. First, cross-trial comparisons are weak evidence: the retatrutide obesity figure comes from an 80-week trial, longer than the 72-week tirzepatide and 68-week semaglutide trials, and the people enrolled differ. The sleep apnea figures use Lilly’s efficacy estimand, which assumes people stayed on treatment, and the TRIUMPH-4 knee result is a company topline, not yet peer reviewed. Second, the SURMOUNT-5 head-to-head trial was open-label and funded by Eli Lilly, which makes tirzepatide (Aronne 2025). In the phase 3 TRIUMPH-1 trial (n=2,339, 80 weeks), adults with obesity and without diabetes lost 25.0% of body weight on 12 mg versus 3.9% on placebo (Human RCT, PubMed 42814954); in TRIUMPH-2, people with type 2 diabetes lost 18.8% versus 5.1% (Human RCT, n=1,152, PubMed 42810372).
Which fits which goal?
These are statements about evidence, not recommendations:
- Semaglutide has more evidence for lowering cardiovascular events (SELECT) and has an approved MASH indication (label). It is the only one of the three approved as a pill for weight management (label).
- Tirzepatide has more evidence for greater weight loss than semaglutide in a direct randomized comparison (SURMOUNT-5), and it is the one approved for obstructive sleep apnea (FDA).
- Retatrutide has the largest average weight losses reported in its own trials (phase 2; TRIUMPH-1; TRIUMPH-2), but no direct comparison with tirzepatide, only a topline head-to-head result against semaglutide in type 2 diabetes, and no outcome data. It is only available inside clinical trials.
Which drug, if any, suits a particular person depends on their health history, other medicines and coverage. A clinician is the person to decide.
Can they be combined?
All three activate the GLP-1 receptor (Jastreboff 2023; approved labels), so taking two of them together would double up on the same pathway. As of 2026-10-29, no controlled human study has tested any combination of retatrutide, tirzepatide and semaglutide. Reports of combined use online are anecdotal and are not evidence.
Safety and regulatory status
Side effects in trials
- Semaglutide: nausea and diarrhea were the most common side effects in STEP 1, and 4.5% stopped for gastrointestinal events vs 0.8% on placebo (Human RCT, n=1,961). In SELECT, 16.6% stopped the drug for adverse events vs 8.2% on placebo (Human RCT, n=17,604). Label warnings include pancreatitis, gallbladder disease, acute kidney injury from dehydration, heart rate increase and aspiration during anesthesia (Approved label).
- Tirzepatide: side effects were mainly gastrointestinal. Between 4.3% and 7.1% of participants stopped for adverse events, depending on dose, vs 2.6% on placebo (Human RCT, n=2,539). Its label warnings are similar to semaglutide’s, including pancreatitis and gallbladder disease (Approved label).
- Retatrutide: in TRIUMPH-2, diarrhea affected 27–34% of participants vs 13% on placebo, and nausea 14–28% vs 8%. Hypotension and dysesthesia were more frequent than with placebo (Human RCT, n=1,152). In TRANSCEND-T2D-1, 2–5% stopped for adverse events vs 0% on placebo (Human RCT, n=537). In the head-to-head TRANSCEND-T2D-2 trial, 4.8% (9 mg) and 7.9% (12 mg) stopped for adverse events vs 2.7% on Ozempic 2 mg, and dysesthesia occurred in 4.8–6.5% vs 2.7% (Lilly topline, n=1,298). No long-term or outcome safety data exist yet.
By jurisdiction
- United States: semaglutide and tirzepatide are prescription drugs. The FDA has reported adverse events, some needing hospitalization, linked to dosing errors with compounded semaglutide. It has also received reports tied to compounded semaglutide or tirzepatide prescribed above label doses (FDA). The FDA has warned sellers of retatrutide labeled “not for human consumption” and telehealth companies that marketed it (FDA).
- European Union: Wegovy (authorized January 2022) and Mounjaro (September 2022) have EU marketing authorizations (EMA Wegovy; EMA Mounjaro).
- United Kingdom: in May 2026 the MHRA seized about 12,000 doses of unlicensed weight-loss medicines, including retatrutide and tirzepatide, from an illicit manufacturing operation (MHRA).
- Sport: GLP-1 drugs are not prohibited, though WADA is monitoring their use (USADA). WADA’s S0 class prohibits at all times any substance without approval from a government health authority, including drugs still in clinical development (USADA). Retatrutide has no approval anywhere, so S0 covers it, although the List names no S0 substances individually. The 2027 List, in force from 2027-01-01, names “peptides” in general under S0 and keeps semaglutide and tirzepatide on the Monitoring Program, tested for but not prohibited (USADA athlete advisory).
How long do effects take in studies?
| Drug (trial) | Reported timeline |
|---|---|
| Retatrutide (phase 2) | −17.5% at 24 wk, −24.2% at 48 wk (12 mg) (link) |
| Retatrutide (TRIUMPH-1) | −25.0% at 80 wk on 12 mg vs −3.9% placebo (link) |
| Retatrutide (TRIUMPH-2) | −11.9% to −18.8% at 80 wk (link) |
| Tirzepatide (SURMOUNT-1) | −15.0% to −20.9% at 72 wk (link) |
| Semaglutide (STEP 1) | −14.9% at 68 wk (link) |
No established human dose exists outside approved labels. For semaglutide and tirzepatide, dosing is set by the FDA label and the prescriber. Retatrutide has no approved dose.
What users report
Everything below reflects unverified self-reports from forums and social media, mostly from people who say they bought these peptides from unregulated online sellers rather than through a prescription — none of it is clinical evidence. Across Reddit, X, YouTube and bodybuilding or biohacking boards, people who post about semaglutide and tirzepatide commonly report reduced appetite and steady weight loss within the first few weeks, alongside nausea, fatigue, constipation, or diarrhea as the most frequent complaints. People who post about retatrutide tend to describe faster or larger weight changes and higher energy, but also mention unusual skin burning or sensitivity, insomnia, and a racing heartbeat more often than users of the other two.
A recurring complaint across all three is injection-site pain, redness, or lumps, which many attribute to product quality rather than the peptide itself. Threads frequently argue about counterfeit or underdosed vials, describing “no effect” stretches that others blame on fake or poorly stored product rather than the compound failing to work. Cost is another constant flashpoint, with posters comparing prices and accusing each other of being scammed by unreliable sources.
Debates also center on which option gives the best results for the least discomfort, with some users claiming retatrutide is dramatically stronger while others say the side effects aren’t worth it compared to tirzepatide or semaglutide. Long-term safety, especially from unregulated sourcing, remains the most contested and least resolved topic in these communities.
Frequently asked questions
Is retatrutide stronger than tirzepatide?
Nobody knows yet. As of 2026-10-29 no trial has reported results against tirzepatide; a phase 3 trial in obesity is still running (TRIUMPH-5). Retatrutide’s own trials report larger average losses, −25.0% at 80 weeks on 12 mg in phase 3 (Human RCT, n=2,339), but they enrolled different people over different lengths of time. Its only head-to-head result so far is against semaglutide in type 2 diabetes (Lilly, 2026-10-28).
Is retatrutide FDA approved?
No. Retatrutide is an investigational drug and is available only inside clinical trials. Lilly plans to submit it to the FDA in the first quarter of 2027 (Lilly, 2026-08-05); its third-quarter report on 2026-10-29 gave no new date (Lilly). The FDA states that it “cannot be used in compounding under federal law”. The agency has also warned companies selling it with labels such as “for research purposes” (FDA). Products sold that way have not been reviewed for purity, identity or dose.
Which causes more weight loss, tirzepatide or semaglutide?
Tirzepatide did in the one direct trial. In SURMOUNT-5, adults with obesity but without diabetes lost 20.2% of body weight on tirzepatide vs 13.7% on semaglutide at 72 weeks (Human RCT, n=751). The trial was open-label and funded by the maker of tirzepatide.
What are the side effects of retatrutide compared with tirzepatide and semaglutide?
All three mainly cause gastrointestinal effects such as nausea and diarrhea. Retatrutide also showed more hypotension and dysesthesia than placebo in phase 3 (Human RCT, n=1,152), as well as dose-dependent heart rate increases in phase 2. Unlike the approved drugs, it has no long-term safety record.
Are semaglutide, tirzepatide or retatrutide banned in sport?
Semaglutide and tirzepatide are not prohibited, but WADA is monitoring GLP-1 use (USADA). Retatrutide is different: WADA’s S0 class prohibits at all times any substance with no government health approval, including drugs in clinical development, so retatrutide is prohibited even though the list names no S0 substances individually (USADA). From 2027-01-01 the 2027 List names “peptides” in general under S0.
References
- Jastreboff AM, et al. (2023). Triple-Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial. N Engl J Med. PubMed 37366315
- Bellido V, le Roux CW, et al. (2026). Retatrutide in adults with obesity and type 2 diabetes (TRIUMPH-2): a phase 3 trial. Lancet. PubMed 42810372
- Bajaj HS, et al. (2026). Efficacy and safety of retatrutide in type 2 diabetes (TRANSCEND-T2D-1): a phase 3 trial. Lancet. PubMed 42250575
- Sanyal AJ, et al. (2024). Triple hormone receptor agonist retatrutide for metabolic dysfunction-associated steatotic liver disease. Nat Med. PubMed 38858523
- Giblin K, et al. (2026). Retatrutide for obesity, obstructive sleep apnea and knee osteoarthritis: design of the TRIUMPH trials. Diabetes Obes Metab. PubMed 41090431
- Structural insights into the triple agonism at GLP-1R, GIPR and GCGR manifested by retatrutide (2024). PMC11255275
- Jastreboff AM, et al. (2022). Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). N Engl J Med. PubMed 35658024
- Aronne LJ, et al. (2025). Tirzepatide as Compared with Semaglutide for the Treatment of Obesity (SURMOUNT-5). N Engl J Med. PubMed 40353578
- Frías JP, et al. (2021). Tirzepatide versus Semaglutide Once Weekly in Patients with Type 2 Diabetes (SURPASS-2). N Engl J Med. PubMed 34170647
- Nicholls SJ, et al. (2025). Cardiovascular Outcomes with Tirzepatide versus Dulaglutide (SURPASS-CVOT). N Engl J Med. PubMed 41406444
- Wilding JPH, et al. (2021). Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1). N Engl J Med. PubMed 33567185
- Lincoff AM, et al. (2023). Semaglutide and Cardiovascular Outcomes in Obesity without Diabetes (SELECT). N Engl J Med. PubMed 37952131
- US FDA. Wegovy (semaglutide) prescribing information, revised 2026. accessdata.fda.gov
- US FDA. Zepbound (tirzepatide) prescribing information, 2026. accessdata.fda.gov
- US FDA. Drugs@FDA entries: Ozempic, Wegovy, Mounjaro, Zepbound.
- US FDA (2026). FDA’s Concerns with Unapproved GLP-1 Drugs Used for Weight Loss (content current as of 2026-09-01). fda.gov
- US FDA (2026-04-30). FDA proposes to exclude semaglutide, tirzepatide and liraglutide from 503B bulks list. fda.gov
- US FDA (2024). FDA Approves First Medication for Obstructive Sleep Apnea. fda.gov
- US FDA (2025). FDA Approves Treatment for Serious Liver Disease Known as “MASH”. fda.gov
- ClinicalTrials.gov: NCT05929066 (TRIUMPH-1), NCT05929079 (TRIUMPH-2), NCT05882045 (TRIUMPH-3), NCT05931367 (TRIUMPH-4), NCT06383390 (TRIUMPH-Outcomes), NCT06260722 (TRANSCEND-T2D-2), NCT05822830 (SURMOUNT-5).
- European Medicines Agency. EPARs: Wegovy; Mounjaro.
- MHRA (2026-05-29). Two arrested during the MHRA’s largest-ever seizure of unlicensed weight-loss medicines. gov.uk
- USADA. Weight Loss Drugs: What athletes need to know about GLP-1s. usada.org
- USADA. What’s New on the 2025 WADA Prohibited List (S0 definition). usada.org
- USADA. Athlete advisory: 2027 Prohibited List (2026-10-06). usada.org
- Grunstein RR, Somers VK, Azarbarzin A, et al. (2026). Retatrutide once weekly for treatment of obstructive sleep apnea (TRIUMPH-1-OSA and TRIUMPH-2-OSA). N Engl J Med, published online 2026-10-21. doi:10.1056/NEJMoa2611477
- Eli Lilly and Company (2025-12-11). TRIUMPH-4 topline results in knee osteoarthritis. investor.lilly.com
- Eli Lilly and Company (2026-08-05). Lilly reports second-quarter 2026 financial results. investor.lilly.com
- Eli Lilly and Company (2026-10-28). Lilly’s retatrutide delivered greater A1C reduction and more than double the weight loss of Ozempic’s highest approved dose in head-to-head trial (TRANSCEND-T2D-2). investor.lilly.com
- Eli Lilly and Company (2026-10-29). Lilly reports third-quarter 2026 financial results. prnewswire.com
Change log
2026-11-02: retatrutide rows updated to phase 3 results (TRIUMPH-1 weight, the two sleep apnea trials published 2026-10-21, TRIUMPH-4 knee topline); sport rows made consistent (S0 covers retatrutide); 2027 WADA List added; reviewed by the editorial team.
2026-10-29: Lilly’s 2026-10-28 head-to-head TRANSCEND-T2D-2 result against Ozempic 2 mg added (summary, key points, evidence table, safety, FAQs); Lilly’s Q1 2027 filing plan and its 2026-10-29 third-quarter report (no new date) added to the FDA question; reviewed by the editorial team.
2026-10-12: links to related entries added; no change to the facts.
2026-10-11: A 2026 observational study comparing heart outcomes on tirzepatide and semaglutide added; reviewed by the editorial team.
2026-10-05: dose column removed from the timeline table (PeptidesView names a dose only to identify a trial result); evidence figure redrawn to match the status box; reviewed by the editorial team.
2026-10-04: retatrutide’s TRIUMPH-1 results added from the peer-reviewed NEJM paper (n=2,339; 25.0% vs 3.9% on placebo); TRIUMPH-2 restated; reviewed by the editorial team.
2026-09-30: added “What users report” (summarised public anecdote, labelled as such).
2026-09-30: first published after review by the editorial team.