Tirzepatide vs Semaglutide: Trial Evidence

How does tirzepatide compare with semaglutide? A direct obesity trial now provides a more useful answer than comparing headlines from unrelated studies. Its results still concern defined prescription formulations, participants and endpoints—not individual predictions or approval of online research vials.

This original FirstLabs editorial review was updated November 3, 2026. It is educational information, not medical advice, a dosing guide or a recommendation for personal use. FirstLabs catalogue materials are for laboratory research only, not human or veterinary use.

Dual GIP/GLP-1 versus GLP-1 receptor activity

Tirzepatide is a single molecule that activates GIP and GLP-1 receptors. Semaglutide is a GLP-1 receptor agonist. These incretin pathways relate to glucose regulation, appetite signalling and gastric emptying, but receptor count alone cannot prove which medicine is best.

Clinical comparisons need a defined population, duration, comparator and outcome. Diabetes trials and obesity trials without diabetes answer different questions; body-weight change and HbA1c are also different endpoints.

SURMOUNT-5: a direct 72-week obesity comparison

The 2025 randomized, open-label SURMOUNT-5 trial enrolled 751 adults with obesity, or overweight with a weight-related condition, without diabetes. Participants received the trial's maximum-tolerated prescription formulations plus diet and physical-activity counselling.

At week 72, mean body-weight reduction was 20.2% with tirzepatide versus 13.7% with semaglutide under the treatment-regimen estimand. The difference is 6.5 percentage points—not “6.5% more fat loss.” This was body-weight change, not a direct measure of fat mass.

Tirzepatide was superior for the study's body-weight and waist-circumference endpoints. That supports a specific comparative conclusion, not universal superiority for every health outcome or every person. The study was open-label, sponsor-funded and did not establish that one treatment was safer overall.

SURMOUNT-1 and SURPASS-2: read results in context

SURMOUNT-1: obesity or overweight without diabetes

The 2022 placebo-controlled trial enrolled 2,539 adults and followed the primary weight endpoint to 72 weeks. The publication's treatment-regimen analysis reported mean reductions of 15.0%, 19.5% and 20.9% across three tirzepatide study groups, versus 3.1% with placebo. These are different groups, not a pooled average or an individual forecast.

You may also see 16.0%, 21.4% and 22.5% quoted from its efficacy estimand, with 2.4% for placebo. That analysis addresses a different statistical question. Mixing one analysis's active result with another analysis's placebo result is misleading.

SURPASS-2: type 2 diabetes, 40 weeks

This active-comparator trial studied adults with type 2 diabetes treated with metformin and found greater mean HbA1c and body-weight reductions with tirzepatide than with the semaglutide comparator studied. Its semaglutide comparator was the diabetes formulation regimen—not the higher weight-management regimens later compared in SURMOUNT-5.

Neither trial supplies evidence that a FirstLabs catalogue vial is equivalent to trial material. Comparing these results with retatrutide percentages from separate studies is not a head-to-head comparison.

Adverse events and the limits of a safety comparison

Gastrointestinal events including nausea, diarrhoea and vomiting were common in the cited trials, generally mild to moderate. In SURMOUNT-1, adverse-event discontinuations were 4.3%, 7.1% and 6.2% in the tirzepatide groups versus 2.6% with placebo. Benefits and treatment discontinuations belong in the same evidence review.

SURMOUNT-5 reported adverse-event discontinuations of 6.1% with tirzepatide and 8.0% with semaglutide, but it was not powered to establish comparative safety or tolerability. A lower discontinuation percentage is not proof of being safer.

Prescription-product information includes important warnings and contraindications beyond these common trial events. The current official product information—not a blog—is the source for medical risk assessment. This article does not provide side-effect management or personal-use protocols.

Canadian prescription authorization does not extend to research vials

Health Canada's Drug Product Database contains authorized prescription tirzepatide products under the Mounjaro and Zepbound names; the Zepbound record reviewed is marketed. These are specific products with their own drug information and authorized indications. Do not transfer one brand's indication to every preparation containing tirzepatide.

FirstLabs research vials are not Mounjaro or Zepbound and are not interchangeable with them. They do not inherit a brand's authorization, manufacturing controls or clinical-trial evidence. Research-use-only labels and COAs do not authorize personal use.

Tirzepatide research: frequently asked questions

Was tirzepatide better than semaglutide in a direct trial?

Yes, for average body-weight and waist-circumference reduction at 72 weeks in SURMOUNT-5's defined population without diabetes. That is not a universal ranking for all outcomes or people.

Will everyone lose 20.2%?

No. It is a study-group average with a specified statistical analysis, not an individual prediction.

Does Canadian approval of Zepbound approve research tirzepatide?

No. Authorization applies to the specific prescription product, not unrelated research vials.

Laboratory documentation is a separate question

Evidence about tirzepatide in a clinical study does not establish that a FirstLabs vial is equivalent to the studied formulation. A certificate of analysis describes the submitted sample, not medical suitability or regulatory authorization. HPLC purity does not by itself establish quantity, sterility, endotoxin control or a match to current stock.

For laboratory records, verify exact identity and labelled size, analytical methods, measured quantity, sample identifiers and any available lot-to-stock documentation. A laboratory task ID is not automatically a manufacturing lot. Keep missing reports and adverse results visible rather than borrowing evidence from another size.

The Tirzepatide Canada documentation page connects the separate 10mg, 20mg and 30mg laboratory catalogue sizes with available sample reports and documentation gaps. These are material quantities, not dose recommendations. See our Retatrutide clinical evidence review for a separate discussion of triple-receptor research and comparison limits.

Read our COA verification checklist, published laboratory reports and Canadian regulation overview for these distinctions. To compare catalogue sizes, CAD prices and report status in one place, see Peptides Canada.

Primary sources and editorial scope

FirstLabs is a research-material supplier with a commercial interest in the compounds discussed, not a licensed pharmacy or an independent medical authority. Results belong to their original study populations, formulations and endpoints. No personal outcome, treatment protocol or authorization of catalogue products is implied.

Tirzepatide vs Semaglutide in Canada: What the Clinical Trials Show