Both are weekly injectables that act on gut hormone receptors, but they are not the same molecule. Here is how they differ in mechanism, trial results, side effects and regulatory status.
Semaglutide and tirzepatide are the two most widely prescribed injectable medications for chronic weight management. They are often lumped together as "GLP-1s," and they do share a lot: both are given once a week, both work through gut hormone pathways, and both carry similar warnings. But they are different molecules with different trial records, and a licensed provider may have good reasons to suggest one over the other. This article lays out the differences without recommending either for you.
Semaglutide is a GLP-1 receptor agonist. It activates the receptor for glucagon-like peptide-1, a hormone that increases fullness, slows stomach emptying and improves insulin response after meals.
Tirzepatide activates that same GLP-1 receptor and also the receptor for GIP (glucose-dependent insulinotropic polypeptide), a second gut hormone. Its prescribing information describes it as a dual GIP and GLP-1 receptor agonist. Exactly how GIP contributes to weight reduction is still being studied, but the combination appears to produce larger average effects on body weight than GLP-1 activity alone.
For several years the only way to compare the two was to look at separate placebo-controlled trials, which had different populations and durations. That changed with SURMOUNT-5, a randomized trial published in the New England Journal of Medicine in 2025 that compared the two medications directly.
The trial enrolled 751 adults with obesity and no diabetes across 32 US sites. Participants received the maximum tolerated dose of either tirzepatide (10 or 15 mg weekly) or semaglutide (1.7 or 2.4 mg weekly) for 72 weeks. Average body weight change was -20.2 percent with tirzepatide versus -13.7 percent with semaglutide. Waist circumference fell by an average of 18.4 cm versus 13.0 cm. Participants on tirzepatide were more likely to reach weight reductions of 10, 15, 20 and 25 percent.
Side effects in the trial were mostly mild to moderate gastrointestinal symptoms occurring during dose escalation. Gastrointestinal events leading to discontinuation were somewhat more common with semaglutide (5.6 percent) than with tirzepatide (2.7 percent), although both numbers are low.
Two cautions when reading this. First, the trial was funded by the maker of tirzepatide, which is standard for registration trials but worth knowing. Second, group averages do not describe individuals. Plenty of people respond very well to semaglutide, and some do not tolerate tirzepatide. A head-to-head average is one input, not a verdict.
For context, the pivotal trials for each medication showed similar patterns:
Both trials included lifestyle counseling, and both reported that most adverse events were gastrointestinal and concentrated in the dose-escalation period.
Weight percentage is not the only outcome that matters. Semaglutide has a completed cardiovascular outcomes trial in people without diabetes. SELECT, published in 2023, randomized 17,604 adults aged 45 or older with established cardiovascular disease and a BMI of 27 or higher to semaglutide 2.4 mg or placebo and followed them for major cardiovascular events. On the basis of that trial, Wegovy's label now includes an indication to reduce the risk of major adverse cardiovascular events in adults with established cardiovascular disease and obesity or overweight. Wegovy also holds an accelerated approval for a form of fatty liver disease (noncirrhotic MASH with moderate to advanced fibrosis).
Tirzepatide's additional approval is for moderate to severe obstructive sleep apnea in adults with obesity. Its cardiovascular outcomes trial in people without diabetes was still ongoing at the time of writing, so for someone whose main concern is heart disease history, the evidence bases are not equivalent yet.
The two labels list very similar warnings: a boxed warning about thyroid C-cell tumors observed in rodents, plus cautions about pancreatitis, gallbladder disease, kidney injury from dehydration, severe gastrointestinal reactions, hypersensitivity, diabetic retinopathy complications in people with type 2 diabetes, and aspiration risk during anesthesia. Both are contraindicated with a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2.
The most common adverse reactions are also the same categories. In the Wegovy label, nausea was reported by 44 percent of participants on 2.4 mg (16 percent on placebo), diarrhea by 30 percent, vomiting by 24 percent and constipation by 24 percent. In the Zepbound label, nausea ranged from 25 to 29 percent across doses (8 percent on placebo), diarrhea 19 to 23 percent, vomiting 8 to 13 percent and constipation 11 to 17 percent. Different trial designs make precise cross-trial comparison unreliable, but the overall picture is that gastrointestinal symptoms are common with both and usually ease as the body adjusts.
Both are weekly subcutaneous injections supplied in pens for the brand products. Each follows a stepwise escalation schedule set by the label and managed by the prescriber. We deliberately do not publish escalation schedules here, because adjusting doses without provider oversight is one of the situations the FDA has flagged in adverse event reports. Semaglutide is also now available as an FDA-approved tablet for weight management, which is covered in the Wegovy label.
Wegovy and Zepbound are the FDA-approved brand products for chronic weight management. Ozempic and Mounjaro contain the same molecules but are approved for type 2 diabetes; prescribing them for weight alone is off-label.
Compounded semaglutide and compounded tirzepatide are prepared by pharmacies and are not FDA-approved. The FDA does not review them for safety, effectiveness or quality, and it has published specific concerns about dosing errors and product handling. The compounded medications available through NewDay Wellness fall into this category, and we say so plainly on every product page.
That is the wrong question, or at least an incomplete one. The honest summary is: tirzepatide produced larger average weight reductions in the only direct comparison to date; semaglutide has a longer track record and a completed cardiovascular outcomes trial in people without diabetes; side effect categories overlap heavily; and cost, availability, insurance coverage and your own health history all weigh on the decision.
In the only direct comparison to date, SURMOUNT-5, tirzepatide produced a larger average weight reduction (-20.2% versus -13.7%). Averages do not describe individuals, and some people respond very well to semaglutide or tolerate it better.
The categories are very similar: nausea, diarrhea, vomiting and constipation are most common, and both labels carry the same boxed warning about thyroid C-cell tumors in rodents. Cross-trial comparisons of exact rates are unreliable.
Semaglutide. The SELECT trial led to a Wegovy indication to reduce major cardiovascular events in adults with established cardiovascular disease and obesity or overweight. Tirzepatide's equivalent trial in people without diabetes was ongoing at the time of writing.
Each pair contains the same active ingredient. Wegovy and Zepbound are approved for chronic weight management; Ozempic and Mounjaro are approved for type 2 diabetes, so using them for weight alone is off-label.
A licensed provider can look at your medical history, your other medications and your goals, and explain which option, if any, makes sense. Nothing in this article determines eligibility or replaces that conversation.
Written by the NewDay Wellness editorial team from the sources above and checked against them before publication, and medically reviewed by Dr. Sean Arora and Dr. Shannon Arora of Arora Health & Aesthetics; see our editorial standards. This article is educational and does not diagnose conditions, establish eligibility for any medication, or replace care from a licensed provider. Compounded medications are not FDA-approved.
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