Head to head
Tirzepatide vs Ozempic: How the Fat-Loss Trials Compare
Published by Peptara Labs · Updated · How we research and check our pages
Mounjaro / Zepbound (tirzepatide) vs Ozempic / Wegovy (semaglutide). Both FDA-approved as brand pens. Tirzepatide is a dual-agonist (GLP-1 + GIP); semaglutide is single-agonist GLP-1. Different trials, not head-to-head in obesity.
Verdict in 4 lines
- Tirzepatide hit -22.5% body weight in SURMOUNT-1 (Phase 3, 72 weeks).
- Semaglutide hit -14.9% in STEP-1 (Phase 3, 68 weeks).
- Different trials, different cohorts. Treat the gap as a data observation, not a head-to-head finding.
- Peptara sells Tirzepatide as a research vial. Peptara does NOT sell semaglutide. Brand semaglutide pens are prescription-only, and their price depends on insurance and pharmacy.
TL;DR comparison
One table, every row that matters. The dose row shows only what each trial or label used, with its source. The recon row assumes the Peptara standard reconstitution (20mg vial in 2mL bac water, 200 units per vial, 0.1mg per unit), which is vial arithmetic, not a dose; semaglutide pens need no reconstitution. See the reconstitution guide for the tirzepatide math.
Mechanism: dual GLP-1 + GIP vs single GLP-1
Both compounds activate the GLP-1 satiety and insulin axis. Tirzepatide adds a second receptor.
Tirzepatide (dual agonist)
Targets two receptor systems: the standard GLP-1 satiety and insulin axis (slows gastric emptying, reduces appetite) plus GIP (glucose-dependent insulinotropic polypeptide), which appears to add fat-mass-loss benefit on top of GLP-1 alone. Sold as Mounjaro (T2D, FDA 2022) and Zepbound (obesity, FDA 2023) brand pens, and as a research vial by Peptara.
View Tirzepatide product
Semaglutide (single GLP-1 agonist)
Targets one receptor system (GLP-1 only). Mature clinical data spans more than 10 years through Ozempic and Wegovy trials, including SUSTAIN (T2D cardiovascular) and SELECT (obesity cardiovascular outcomes). Sold as Ozempic (T2D, FDA 2017) and Wegovy (obesity, FDA 2021) brand pens. Peptara does not sell semaglutide.
Honest trade-off: more receptor activation drives a stronger fat-loss signal in Phase 3 trials, but semaglutide has the longer real-world safety record. For the GLP-1 + GIP + glucagon triple-agonist (Retatrutide), see Retatrutide vs Tirzepatide.
Clinical trial results
Headline figures, trial citations, and the disclaimer that has to come with them.
Tirzepatide Phase 3 (SURMOUNT-1)
- Reference: Jastreboff et al, NEJM 2022;387(3):205-216
- Phase: 3
- n: 2,539 (no T2D)
- Duration: 72 weeks
- 15mg/wk: -22.5% mean body weight
- 10mg/wk: -19.5% · 5mg/wk: -15.0% · Placebo: -2.4%
Semaglutide Phase 3 (STEP-1)
- Reference: Wilding et al, NEJM 2021;384(11):989-1002
- Phase: 3
- n: 1,961 (no T2D)
- Duration: 68 weeks
- 2.4mg/wk: -14.9% mean body weight
- Placebo: -2.4%. Trial supported the 2021 Wegovy FDA approval.
Read this before quoting either number
Different trials, not head-to-head in obesity. SURMOUNT-1 ran 72 weeks; STEP-1 ran 68 weeks. Different cohorts, different sponsors, different placebo response calibration. The 7.6 percentage-point gap is a data observation across trials, not a controlled head-to-head finding.
Note on SURPASS-2 (Frias et al, NEJM 2021): this was a head-to-head trial between tirzepatide and semaglutide, but in TYPE 2 DIABETES (not obesity) at lower doses (tirzepatide 15mg vs semaglutide 1mg, 40 weeks). At those doses tirzepatide reduced body weight 11.2kg vs semaglutide 5.7kg. Useful directional signal, but the patient population is T2D and the semaglutide dose ceiling was the T2D-label 1mg. SURPASS-2 is not a head-to-head obesity comparison.
FDA and regulatory status
Both compounds are FDA-approved as brand pens. This is the symmetric case in the /vs/* cluster. The asymmetry is format: brand pens vs research vial.
Tirzepatide brand pens (Eli Lilly)
- Mounjaro: FDA-approved May 13, 2022. Indication: type 2 diabetes. Max dose 15mg/wk.
- Zepbound: FDA-approved Nov 8, 2023. Indication: chronic weight management. Max dose 15mg/wk.
Semaglutide brand pens (Novo Nordisk)
- Ozempic: FDA-approved Dec 5, 2017. Indication: type 2 diabetes. Max dose 2mg/wk.
- Wegovy: FDA-approved Jun 4, 2021. Indication: chronic weight management. Max dose 2.4mg/wk.
Peptara format and scope
Peptara stocks Tirzepatide as a RESEARCH compound (vial format) for international research customers. Single vials are currently sold out and available in the Lumen research stack. The brand pens (Mounjaro, Zepbound, Ozempic, Wegovy) are FDA-approved finished pharmaceuticals available only via prescription in their approved markets. Peptara does not sell brand pens and does not sell semaglutide in any form.
Side effects
Both share the GI-dominant GLP-1 class profile. Notes below are not exhaustive.
Shared (GLP-1 class)
- Nausea, most pronounced during titration
- Diarrhea
- Constipation
- Vomiting at higher doses
- Typically resolve over 4 to 8 weeks at a given dose
Semaglutide-specific
- Years of clinical safety data (SUSTAIN, SELECT)
- FDA black-box warning: thyroid C-cell tumors (rodent data)
- Gastroparesis case reports at high cumulative exposure
- Rare pancreatitis and gallbladder events
Tirzepatide-specific
- SURMOUNT-1: nausea about 30% at 15mg vs about 10% placebo
- Lower hypoglycemia risk than insulin combinations (T2D context)
- Same GLP-1 class thyroid C-cell black-box warning
- Dual agonism may amplify early-week GI in some users
Both trials raised the dose in steps under medical supervision, which the trial reports describe as part of how gastrointestinal effects were kept mostly mild to moderate (Jastreboff et al., 2022; Wilding et al., 2021). That describes how the trials ran, not a plan for anyone to follow. Stop and consult a licensed physician for severe or persistent GI symptoms, signs of pancreatitis, or any unusual side effect.
Doses as studied in each trial
SURMOUNT-1 assigned 2,539 adults to tirzepatide 5, 10 or 15 mg once weekly, or to placebo, for 72 weeks (Jastreboff et al., 2022; doi:10.1056/NEJMoa2206038). STEP-1 assigned 1,961 adults to semaglutide 2.4 mg once weekly or placebo for 68 weeks (Wilding et al., 2021). These are the amounts the trials tested, reported for education. They are not a schedule, and no amount here is a dose for anyone to take.
| Compound | Weekly dose arm (trial) | Route | Mean body-weight change | Source |
|---|---|---|---|---|
| Tirzepatide | 5 mg | Subcutaneous, once weekly | -15.0% at 72 weeks | Jastreboff et al., 2022 (SURMOUNT-1, phase 3) |
| Tirzepatide | 10 mg | Subcutaneous, once weekly | -19.5% at 72 weeks | Jastreboff et al., 2022 (SURMOUNT-1, phase 3) |
| Tirzepatide | 15 mg | Subcutaneous, once weekly | -22.5% at 72 weeks | Jastreboff et al., 2022 (SURMOUNT-1, phase 3) |
| Placebo (tirzepatide trial) | None | Subcutaneous, once weekly | -2.4% at 72 weeks | Jastreboff et al., 2022 (SURMOUNT-1, phase 3) |
| Semaglutide | 2.4 mg | Subcutaneous, once weekly | -14.9% at 68 weeks (placebo -2.4%) | Wilding et al., 2021 (STEP-1, phase 3) |
Both trials reached the higher amounts in steps under medical supervision. The brand labels set their own escalation for prescribed use, with label maximums of 15 mg once weekly for Mounjaro and Zepbound, 2.4 mg once weekly for Wegovy, and 2 mg once weekly for Ozempic. The tirzepatide dosage page covers the trial arms in more detail.
Vial math, not a dose: a 20mg tirzepatide vial mixed with 2mL of bacteriostatic water gives 200 units on a U-100 syringe, so each unit holds 0.1mg. Reading a decimal place wrong on a small syringe barrel is the most common source of a tenfold misread, which is why the arithmetic is shown in units rather than mL. Semaglutide pens are pre-filled and need no reconstitution. See /reconstitution for the U-100 math (1 unit equals 0.01mL). Peptara does not sell semaglutide.
Price: tirzepatide per vial and per mg
A 20mg tirzepatide vial is $78 with email signup and $92 retail, which is $3.90 and $4.60 per mg. Tirzepatide is kit-only: single vials currently sold out, available in the Lumen research stack. Semaglutide is not sold by Peptara, so its price is not quoted here.
Tirzepatide via Peptara
$78 with email signup per 20mg vial ($92 retail); single vials currently sold out, available in the Lumen research stack
Price of each SURMOUNT-1 trial arm's weekly amount at the per-mg rate (Jastreboff et al., 2022). This is price arithmetic on the trial's arms, not a dose recommendation, and it does not divide a vial into weeks.
- 5 mg trial arm: $19.50 of material a week with email signup, $23 retail
- 10 mg trial arm: $39 of material a week with email signup, $46 retail
- 15 mg trial arm: $58.50 of material a week with email signup, $69 retail
Semaglutide (NOT sold by Peptara)
Prescription brand pens
- Ozempic and Wegovy are prescription pens. What a patient pays depends on insurance, the pharmacy, and the manufacturer's current programs, so this page does not quote a figure.
- Peptara does not sell semaglutide in any form and does not source or recommend gray-market semaglutide.
Why there is no single cost ratio
Tirzepatide is priced per milligram of research material; brand semaglutide is priced per prescription pen, with insurance and pharmacy terms on top. The regulatory status also differs: both semaglutide brands and both tirzepatide brands are FDA-approved, while Peptara sells research-grade tirzepatide, not a finished pharmaceutical. A single cost ratio between the two would mislead, so this page gives the tirzepatide figures and the arithmetic instead. For the full tirzepatide breakdown, see the tirzepatide price per vial.
Who picks which
Three short profiles. No single right answer, just trade-offs that map to user context.
Pick Wegovy / Ozempic if
- You want an FDA-approved obesity drug via prescription
- You have prescription access, with insurance or cash coverage for a brand pen
- You want the longest-duration safety record (SELECT cardiovascular)
- You prefer a pre-filled pen with no reconstitution
Pick Tirzepatide via Peptara if
- You accept a research-vial format (units on a U-100 syringe)
- You want the larger Phase 3 trial effect (-22.5% vs -14.9%)
- You want the lower-cost path (a 20mg research vial at $78 with email signup, $92 retail; single vials currently sold out, available in the Lumen research stack)
- You are outside the US Rx market for brand pens
Pick Retatrutide if
- You want the LARGEST trial effect (-24.2% Phase 2 at 12mg/wk)
- You accept Phase 3 data is still being collected
- You are already comfortable with the research-vial format
- See Retatrutide vs Tirzepatide and Retatrutide vs Ozempic for the reta comparisons
Frequently asked questions
Is tirzepatide really better than Ozempic for weight loss?
Phase 3 SURMOUNT-1 peak was -22.5% body weight at 15mg/wk over 72 weeks for tirzepatide (Jastreboff et al, NEJM 2022). Phase 3 STEP-1 peak was -14.9% at 2.4mg/wk over 68 weeks for semaglutide / Wegovy (Wilding et al, NEJM 2021). The 7.6 percentage-point gap is a data observation across separate trials with different cohorts, different sponsors, different durations. The SURPASS-2 trial was head-to-head between tirzepatide and semaglutide, but in TYPE 2 DIABETES at lower doses (tirz 15mg vs sema 1mg, 40 weeks), useful as a directional signal but not an obesity head-to-head.
Are Mounjaro and Zepbound the same as tirzepatide?
Yes. Both are brand-name tirzepatide manufactured by Eli Lilly. Mounjaro was FDA-approved May 2022 for type 2 diabetes with a maximum dose of 15mg/wk. Zepbound was FDA-approved November 2023 specifically for chronic weight management in adults with BMI of 30 or higher (or 27 with a comorbidity), same 15mg/wk maximum. Same molecule, different on-label indications.
Are Ozempic and Wegovy the same as semaglutide?
Yes. Both are brand-name semaglutide from Novo Nordisk. Ozempic was FDA-approved December 2017 for type 2 diabetes (max 2mg/wk). Wegovy was FDA-approved June 2021 for chronic weight management (max 2.4mg/wk). Same molecule, different titration ceiling, different on-label indications.
Why is Peptara tirzepatide so much cheaper than the brand pens?
Two reasons, and neither depends on a dose. First, format: Peptara ships a freeze-dried research vial that the user reconstitutes with bacteriostatic water, while brand pens are pre-filled finished pharmaceuticals carrying cold-chain logistics, FDA-approval-grade quality assurance, pharmacy distribution, and Novo Nordisk or Eli Lilly margin. Second, market: Peptara serves international research customers, not the US prescription market. The molecule is the same; the regulatory pathway and supply chain are not. Brand pen prices depend on insurance and pharmacy, so a single ratio between the two would mislead.
Does Peptara sell Ozempic or Wegovy?
No. Peptara does NOT sell semaglutide in any form. Peptara is a research-peptide supplier; brand pens are finished pharmaceuticals available only via prescription. Anyone selling "Wegovy from Vietnam" online is selling gray-market product with no chain-of-custody guarantee. Peptara stocks Tirzepatide as a research vial (the same molecule as Mounjaro / Zepbound), not as a brand pen. Single vials are currently sold out and available in the Lumen research stack.
What are the side effects of tirzepatide vs semaglutide?
Both share the GLP-1 class side-effect profile: nausea, diarrhea, constipation, vomiting. Most pronounced during titration and at higher doses; usually resolve over 4 to 8 weeks at a given dose. SURMOUNT-1 reported nausea in roughly 30% at peak 15mg/wk tirzepatide vs roughly 10% placebo. Semaglutide has the longer safety record (SUSTAIN cardiovascular outcomes trial in T2D, SELECT cardiovascular trial in obesity). Both carry the GLP-1 class thyroid C-cell black-box warning (rodent signal; no confirmed human cases).
Can I switch from Ozempic to tirzepatide?
That is a medical decision for the prescribing physician. Do not stop or change FDA-approved therapy without the prescribing doctor. This site gives no switching, washout or starting-dose instructions, and Peptara does not provide medical advice.
How does this compare to retatrutide?
Retatrutide is a triple-agonist (GLP-1 + GIP + glucagon) currently in Phase 3 (TRIUMPH program, Eli Lilly). Phase 2 peak was -24.2% body weight at 12mg/wk over 48 weeks (Jastreboff et al, NEJM 2023). Larger trial effect than both tirzepatide and semaglutide, but Phase 3 data is still being collected and retatrutide is not yet FDA-approved. See the Retatrutide vs Tirzepatide and Retatrutide vs Ozempic comparison pages for the full breakdowns.
Next steps
Buy Tirzepatide via Peptara
20mg vial, $78 with email signup / $92 retail. Same molecule as Mounjaro / Zepbound, research-vial format. Ships from HCMC with COA on request.
View product
How to reconstitute your vial
4-step method, units-not-mL math, calculator for the catalog vials. Required reading before your first tirzepatide injection.
Open guide
Retatrutide vs Tirzepatide
Triple vs dual agonist, Phase 2 -24.2% vs Phase 3 -22.5% trial peaks. The next-generation comparison side by side.
Open comparison
Questions on tirzepatide vs Ozempic
Questions about tirzepatide vs Ozempic? Message the Peptara team on WhatsApp. We answer protocol questions, not medical questions.
Every Tirzepatide order ships with bac water sized to the vial, a written reference in units (never mL), and ongoing order support.