The three biggest weight-loss drugs of the 2020s pull different sets of metabolic levers — one, two, and three respectively. The differences in the trial data are larger than most articles will tell you, and the right one for you depends on more than just the headline weight-loss number. This is the comparison, sourced and current.
Tirzepatide (Zepbound) is currently the most effective FDA-approved drug for weight loss — pivotal trials show roughly 1.5× the average weight reduction of Semaglutide. Semaglutide (Wegovy) is the only one approved for cardiovascular risk reduction in adults with established heart disease and excess weight. Retatrutide is shaping up to surpass both — Phase 3 readouts in late 2025 produced the largest weight loss of any obesity drug ever tested — but it isn't approved yet, with FDA submission expected late 2026 / early 2027.
Which one is right for you depends on three things, in this order: what you're treating (diabetes, obesity, sleep apnea, cardiovascular risk), what your insurance will actually cover, and what side-effect profile you can live with.
Mean placebo-subtracted body-weight reduction in the pivotal trial for each drug, at the highest commercial dose. Trial durations vary (68–72 weeks for Semaglutide and Tirzepatide, 48 weeks for Retatrutide Phase 3), so the bars aren't apples-to-apples on time — but they're the headline numbers you'll see referenced everywhere else.
Sources: STEP-1 (Wilding et al., NEJM 2021), SURMOUNT-1 (Jastreboff et al., NEJM 2022), Phase 2 retatrutide (Jastreboff et al., NEJM 2023), Lilly TRIUMPH-4 readout (December 2025). All highest-dose arms.
Roughly speaking: every additional metabolic lever a drug pulls produces another ~5–7% of mean body-weight reduction in trials. Semaglutide pulls one (GLP-1). Tirzepatide pulls two (GLP-1 + GIP). Retatrutide pulls three (GLP-1 + GIP + glucagon). The pattern in the trial data is remarkably linear so far, though Retatrutide's Phase 3 readout is more recent and the long-term durability picture is less complete.
None of this is what most people experience individually. Trial averages bury substantial variation — some patients lose 30%+ on Semaglutide; some plateau at 8% on Tirzepatide. The means are useful for comparison; they're not promises.
Mechanism, indications, dosing, side effects, cost, access — all in one table. Most-recent FDA labels and trial data, current as of May 2026.
| Semaglutide | Tirzepatide | Retatrutide | |
|---|---|---|---|
| Brand names | Ozempic (T2D), Wegovy (obesity), Rybelsus (oral T2D) | Mounjaro (T2D), Zepbound (obesity, OSA) | None yet (investigational; Eli Lilly) |
| Mechanism | GLP-1 receptor agonist | GLP-1 + GIP dual agonist | GLP-1 + GIP + glucagon triple agonist |
| Approval status (US) | FDA-Approved | FDA-Approved | Investigational |
| Approved indications | Type 2 diabetes; weight loss (BMI 30+, or 27+ with comorbidity); cardiovascular risk reduction; FLOW: kidney disease in T2D | Type 2 diabetes; weight loss (same BMI thresholds); moderate-to-severe OSA in adults with obesity (Dec 2024 — first drug ever approved for OSA) | None yet — Phase 3 ongoing for obesity, T2D, fatty liver disease, knee osteoarthritis |
| Mean weight loss at highest dose, vs. placebo |
−14.9% STEP-1 trial, 68 weeks, 2.4mg |
−22.5% SURMOUNT-1, 72 weeks, 15mg |
−24.2% (Ph2) / −28.7% (Ph3) TRIUMPH-4, 48 weeks, 12mg |
| Half-life | ~165 hours (~7 days) | ~120 hours (~5 days) | ~144 hours (~6 days) |
| Dosing | Weekly subcutaneous injection (Wegovy/Ozempic) or daily oral pill (Rybelsus) | Weekly subcutaneous injection only | Weekly subcutaneous injection (clinical trial protocol) |
| Maximum approved dose | 2.4 mg/week (Wegovy); 2 mg/week (Ozempic); 14 mg/day oral | 15 mg/week | 12 mg/week (trial) |
| Boxed warning | Thyroid C-cell tumors (rodent studies) — contraindicated in personal/family MTC or MEN2 | Thyroid C-cell tumors — same MTC/MEN2 contraindication | Likely the same class warning at approval; not formally labeled yet |
| Most common side effects | Nausea (40%+), diarrhea (~30%), vomiting, constipation, gallbladder events; pancreatitis (rare) | Nausea (~30%), diarrhea, vomiting, constipation, gallbladder events; pancreatitis (rare). Tolerability slightly favored vs Semaglutide in head-to-head (SURPASS-2). | Same GLP-1 class GI profile in trials. Modest dose-dependent heart-rate increase (~6 bpm at 12mg) from glucagon-receptor activation; reversible. |
| List price (US, May 2026) | ~$1,300/mo (Wegovy); ~$1,000/mo (Ozempic) before insurance/savings | ~$1,060/mo (Zepbound); ~$1,070/mo (Mounjaro). Vials via Lilly Direct: ~$500/mo for some doses. | Not commercial yet. Trial-only access. |
| Insurance coverage | Often covered for T2D, variable for obesity, increasingly covered for CV indication post-March 2024 | Often covered for T2D and OSA; increasingly covered for obesity | N/A until approval |
| Compounded versions | Permitted only during FDA shortage. Resolved February 21, 2025; enforcement deadlines ran through May 2025. | Same. Resolved October 2, 2024; enforcement deadlines ran through early 2025. | Anything sold as "compounded retatrutide" is research-grade synthesis, not the manufacturer's clinical material |
Throughout the FDA shortage period, licensed compounding pharmacies were permitted to produce versions of Semaglutide and Tirzepatide under the Section 506C exception. Tirzepatide was officially removed from the shortage list on October 2, 2024; semaglutide on February 21, 2025. Phased enforcement deadlines for compounders ran through May 2025, and the compounding exception expired then. If you encounter a clinic still offering "compounded GLP-1" at a steep discount in 2026, it is no longer operating under the FDA shortage exception. (See: our full analysis of what compounded GLP-1 actually means in 2026.) The brand-name medications and Lilly Direct's Zepbound vial program are the legitimate access paths.
All three are gut-hormone analogues. They mimic signals your body already makes after a meal. The difference is how many hormones each one mimics — and the more, the more weight loss in trials so far.
Semaglutide is an engineered version of GLP-1 (glucagon-like peptide-1), a hormone your gut releases after eating. GLP-1's job is to tell your pancreas to release insulin, slow your stomach emptying, and signal your brain that you're full. Natural GLP-1 lasts a few minutes; Semaglutide is engineered to last about a week.
Tirzepatide hits GLP-1 plus GIP (glucose-dependent insulinotropic polypeptide), a second gut hormone that helps regulate insulin and how the body stores fat. The combination produces a stronger appetite-suppressing and blood-sugar-lowering effect than GLP-1 alone — that's the mechanistic reason for the bigger weight-loss number in SURMOUNT-1.
Retatrutide adds glucagon to the mix. Counterintuitively, glucagon (which normally raises blood sugar) increases resting energy expenditure — your body burns more energy at baseline. So retatrutide combines the appetite suppression of GLP-1, the metabolic effects of GIP, and the energy expenditure boost of glucagon. That's the mechanism behind the largest weight-loss numbers in any obesity trial to date.
Type 2 diabetes (Ozempic, original 2017 indication). Long-term weight management (Wegovy, 2021) for adults with BMI 30+ or BMI 27+ with at least one weight-related comorbidity. Cardiovascular risk reduction (Wegovy, March 2024) for adults with established cardiovascular disease and BMI 27+ — based on the SELECT trial, which showed a 20% reduction in major adverse cardiovascular events. Kidney disease in T2D (FLOW trial readout, 2024) — newest addition.
Type 2 diabetes (Mounjaro, 2022). Long-term weight management (Zepbound, 2023) — same BMI thresholds as Wegovy. Moderate-to-severe obstructive sleep apnea (Zepbound, December 2024) for adults with obesity — the first FDA-approved drug for OSA, ever. The OSA trial (SURMOUNT-OSA) showed roughly 50% remission of apnea events at the 15mg dose.
Not yet approved. Phase 3 program (TRIUMPH) covers obesity, T2D, knee osteoarthritis, and metabolic-associated fatty liver disease (MAFLD). TRIUMPH-4 (osteoarthritis + obesity) read out positive in December 2025. Lilly's expected NDA filing is late 2026 / early 2027. Realistic earliest approval: mid-to-late 2027.
Type 2 diabetes: All three; Tirzepatide produces the largest A1C reductions in head-to-head trials (SURPASS-2 vs Semaglutide).
Pure weight loss: Tirzepatide currently leads approved options.
Cardiovascular risk + overweight: Semaglutide is the only one with this approved indication.
Sleep apnea: Tirzepatide is the only one approved.
Kidney disease in diabetes: Semaglutide (FLOW indication) is the most relevant approved option.
The three drugs share a class safety profile. There are real risks that aren't always headlined in patient-facing marketing — these are the ones a careful prescriber will discuss with you.
All three carry (or are expected to carry) a boxed warning for thyroid C-cell tumors based on rodent studies. This means they are contraindicated in anyone with a personal or family history of medullary thyroid carcinoma (MTC) or Multiple Endocrine Neoplasia syndrome type 2 (MEN2). The translation to human risk is uncertain, but the contraindication is clear.
Acute pancreatitis is rare but documented across the GLP-1 class. Anyone with a history of pancreatitis should discuss this risk with their prescriber before starting any of these drugs.
Increased rates of cholelithiasis (gallstones) and cholecystitis (gallbladder inflammation) are reported across the class, particularly with rapid weight loss.
Nausea, vomiting, diarrhea, and constipation are the most common adverse events, dose-dependent, and usually subside as patients titrate up to maintenance doses. Severe gastroparesis and rare cases of small bowel obstruction (ileus) have been reported — these are the "GLP-1 ileus" cases that occasionally surface in news coverage.
Not for use during pregnancy. Because of Semaglutide's long half-life, a two-month wash-out before attempting conception is generally recommended. Same logic applies to Tirzepatide and Retatrutide.
The triple-agonist mechanism activates glucagon receptors in addition to GLP-1 and GIP. This produces a modest dose-dependent increase in resting heart rate (~6 bpm at the 12mg dose in trials), which is reversible on discontinuation. No major novel safety signals have emerged from Phase 2 or the available Phase 3 readouts, but the long-term safety database is necessarily smaller than for the approved drugs.
List prices in the United States as of May 2026. Real-world cost depends heavily on insurance, manufacturer savings programs, and which formulation you're prescribed. The numbers below are cash-pay before any of those.
List price approximately $1,300/month for Wegovy and ~$1,000/month for Ozempic. Novo Nordisk runs a savings program that can reduce out-of-pocket cost meaningfully for patients with commercial insurance. Insurance coverage varies: Type 2 diabetes is generally covered; weight-loss-only indication is uneven across employer plans (often requires prior authorization, BMI documentation, and step therapy). The new cardiovascular indication has expanded coverage somewhat — Medicare now covers Wegovy for the CV indication in patients with established cardiovascular disease.
List price approximately $1,060/month for Zepbound and similar for Mounjaro. Eli Lilly runs Lilly Direct — a direct-to-patient program offering Zepbound vials (rather than auto-injector pens) at substantially lower cost (around $500/month for some doses) for cash-pay customers. Insurance picture is similar to Semaglutide; the OSA indication has opened up coverage paths that didn't exist before.
Not commercially available. The only legitimate access path today is enrollment in an active TRIUMPH trial — search ClinicalTrials.gov for retatrutide. Anything sold online claiming to be retatrutide is research-grade synthesis with no manufacturing oversight or known purity profile, not the clinical-grade molecule.
No drug comparison can substitute for a conversation with a prescriber who knows your full medical history. But here's the framework most thoughtful clinicians actually use, in plain English:
Either Semaglutide (Ozempic) or Tirzepatide (Mounjaro) is appropriate. Tirzepatide produces larger A1C reductions in head-to-head trials.
Lean: TirzepatideTirzepatide (Zepbound) delivers more weight loss in trials. Semaglutide (Wegovy) has a longer real-world track record and broader patient experience reports.
Lean: TirzepatideSemaglutide (Wegovy) is the only drug with a specific FDA approval for cardiovascular risk reduction in this population, based on the SELECT trial.
Lean: SemaglutideTirzepatide (Zepbound) is the first and only FDA-approved drug for moderate-to-severe OSA in adults with obesity, based on SURMOUNT-OSA.
Lean: TirzepatideSemaglutide has the FLOW trial data and a kidney indication in T2D. Newest data among the three.
Lean: SemaglutideRetatrutide is on track to surpass both. If approval timeline (mid–late 2027) works for you and you're willing to switch later, current Tirzepatide use is a reasonable bridge.
Lean: Wait, then Retatrutide1. Given my medical history (specifically: any thyroid history, pancreatitis, gallbladder issues, pregnancy plans), which of these is safest for me to start?
2. What does my insurance actually cover, and what's the prior authorization path?
3. If I tolerate this poorly, what's the plan — switch, dose-reduce, or stop?
Every number on this page traces back to a primary source — FDA approval letters, peer-reviewed pivotal trials, manufacturer financial disclosures. Read further:
Each of these three peptides has its own full entry in the catalogue — mechanism, half-life, dosing, regulatory status, sources.
Open the catalogue