This is the highest-volume comparison query in the metabolic peptide space - thousands of monthly US searches asking which molecule does what, which is "better", and how the two stack up on cost. It also happens to be the comparison most often answered with marketing fluff rather than data. This piece walks through what the actual published trials say.
RUO framing throughout. Mounjaro / Zepbound (tirzepatide) and Ozempic / Wegovy (semaglutide) are FDA-approved prescription medicines. New-U supplies research-grade equivalents - GLP-1 RC-T (tirzepatide) and GLP-1 RC-S (semaglutide) - strictly as laboratory reagents, not as substitutes for the licensed products.
Semaglutide is a single-receptor GLP-1 agonist. Tirzepatide is a dual GLP-1 + GIP agonist. In the only published head-to-head trial (SURPASS-2), tirzepatide outperformed semaglutide on both HbA1c reduction and weight loss in T2D patients - and cross-trial comparison of obesity endpoints points the same direction at population level.
| Attribute | Semaglutide | Tirzepatide |
|---|---|---|
| Development code | NN9535 | LY3298176 |
| Manufacturer | Novo Nordisk | Eli Lilly |
| Brand names | Ozempic (T2D), Wegovy (obesity), Rybelsus (oral T2D) | Mounjaro (T2D), Zepbound (obesity, OSA-with-obesity) |
| Receptor targets | GLP-1 only | GLP-1 + GIP (dual) |
| FDA approval (T2D) | 2017 | May 2022 |
| FDA approval (obesity) | June 2021 | November 2023 |
| Top weekly dose | 2.4mg (Wegovy) | 15mg (Zepbound) |
| Pivotal obesity trial | STEP-1 (NEJM 2021) | SURMOUNT-1 (NEJM 2022) |
| Trial weight loss (top dose) | ~14.9% at 68 weeks | ~22.5% at 72 weeks |
| Head-to-head T2D outcome | SURPASS-2: HbA1c -1.86% at 1mg | SURPASS-2: HbA1c -2.30% at 15mg (superior) |
| CV outcomes evidence | SELECT (positive, 2023) | SURPASS-CVOT, SUMMIT (pending / partial) |
| US list price (monthly) | ~$900-1,300 | ~$1,000-1,300 |
| Research-grade equivalent | GLP-1 RC-S | GLP-1 RC-T |
Both peptides hit the GLP-1 receptor - which is what produces the appetite-suppression, slowed-gastric-emptying, glucose-dependent insulin-secretion effect that's been driving the entire weight-loss conversation since semaglutide launched.
Tirzepatide adds a second receptor target: GIP (glucose-dependent insulinotropic polypeptide). The biology was historically counter-intuitive - GIP receptor activation alone was associated with weight gain in earlier research. But when combined with GLP-1 activation, GIP appears to produce additional metabolic benefit: enhanced insulin secretion, improved adipose lipid handling, and additional weight loss on top of what GLP-1 alone delivers.
The mechanistic punchline: tirzepatide gives you GLP-1's appetite-and-glucose effects plus a second metabolic lever that semaglutide can't pull. For the longer mechanistic discussion, see our tirzepatide research guide.
SURPASS-2 (Frias JP et al., NEJM, 2021) was the only large randomised head-to-head trial between tirzepatide and semaglutide. The setup:
| Arm | HbA1c change | Mean weight loss |
|---|---|---|
| Semaglutide 1mg | -1.86% | ~5.7 kg |
| Tirzepatide 5mg | -2.01% | ~7.6 kg |
| Tirzepatide 10mg | -2.24% | ~9.3 kg |
| Tirzepatide 15mg | -2.30% | ~11.2 kg |
All three tirzepatide doses beat semaglutide 1mg on both endpoints. The 15mg arm produced roughly double the weight loss of the semaglutide arm and a ~0.44% larger HbA1c reduction.
Important caveat. SURPASS-2 used semaglutide at 1mg - the T2D dose. The obesity dose of semaglutide is 2.4mg (Wegovy). There has not yet been a head-to-head trial of tirzepatide 15mg vs semaglutide 2.4mg in an obesity population. The cross-trial comparison (SURMOUNT-1 ~22.5% vs STEP-1 ~14.9%) is suggestive but is not a randomised head-to-head endpoint.
| Trial | Drug | Top dose | Duration | Mean weight loss | Achieving ≥20% |
|---|---|---|---|---|---|
| STEP-1 (2021) | Semaglutide | 2.4mg weekly | 68 weeks | ~14.9% | ~32% |
| SURMOUNT-1 (2022) | Tirzepatide | 15mg weekly | 72 weeks | ~22.5% | ~57% |
Different populations, different durations, different sponsors, different sites. The numbers are real but the comparison is approximate. A head-to-head SURMOUNT-vs-STEP-style trial in an obesity population has not yet been published - which is one reason the comparison-intent search query stays so high.
| Channel | Semaglutide | Tirzepatide |
|---|---|---|
| US prescription list price | ~$900-1,300/mo | ~$1,000-1,300/mo |
| Insurance coverage | Patchy for obesity; better for T2D | Patchy for obesity; OSA-with-obesity coverage expanding |
| Compounded versions | Off-shortage; 503A pathway closed | Off-shortage; 503A pathway closed |
| Research-grade reagent | GLP-1 RC-S | GLP-1 RC-T |
| EU / UK availability | Wegovy widely available; NHS specialist-only | Mounjaro / Zepbound widely available; NHS access limited |
Both have come off the FDA shortage list, which means US compounding pharmacies operating under 503A and 503B can no longer compound them as a routine workaround. Patients without insurance coverage of the licensed brands face the full list price - which is the structural reason the research-grade reagent market has scaled in this space.
Status check. Mounjaro, Zepbound, Ozempic and Wegovy are FDA-approved prescription medicines and the decision between them is a licensed-prescriber decision, not research-blog content. New-U supplies research-grade tirzepatide (GLP-1 RC-T) and semaglutide (GLP-1 RC-S) as laboratory reagents only - not substitutes for the licensed drugs. Both molecules are also on the WADA Prohibited List (S2) and banned in any sanctioned competition.
Sealed vials of research-grade tirzepatide and semaglutide, >99% HPLC purity by Janoshik / Freedom Diagnostics. Research use only - not for human consumption. Not a substitute for licensed prescriptions. WADA-prohibited in sanctioned competition.
Browse the GLP-1 catalog