Mounjaro vs Semaglutide

Key differences

This pair sets a brand against an ingredient, and the ingredient is not the one in the brand. Mounjaro contains tirzepatide.¹ Semaglutide is the active ingredient in three Novo Nordisk brands: Ozempic, Wegovy and Rybelsus.⁸⁹¹⁰ So the comparison is between two molecules, and between one product and a family of products.

Built on different hormones

Both drugs are lab-made peptides modeled on natural hormones, but on different ones.¹⁸ Tirzepatide is a 39-amino-acid chain based on the sequence of GIP.³¹ It carries a building block called aminoisobutyric acid (Aib) at positions 2 and 13, an amide at its tail end, and a C20 fatty diacid chain linked to the lysine at position 20.¹ Its formula is C225H348N48O68, and its molecular weight is 4813.53 Da.¹

Semaglutide is built on human GLP-1. Compared with the natural hormone, it has two amino acid swaps: Aib at position 8 and arginine at position 34.⁵ A C18 fatty diacid is attached through a spacer to the lysine at position 26.⁶ Its formula is C187H291N45O59, its molecular weight 4113.58 g/mol, and its peptide backbone is made by yeast fermentation.⁶

In both drugs, the fatty acid chain binds albumin, a blood protein, which extends the half-life.¹⁵⁶ Tirzepatide's half-life is about 5 days and semaglutide's about 1 week, and both are injected once a week.¹⁸

One receptor or two

Semaglutide works through one receptor, the GLP-1 receptor.⁸ Tirzepatide works through two, the GIP and GLP-1 receptors.¹ In laboratory receptor-binding studies, tirzepatide bound the GIP receptor about as strongly as natural GIP, but bound the GLP-1 receptor about 5 times more weakly than natural GLP-1.⁴

Their effects on blood sugar overlap. Each one boosts insulin release and trims glucagon in a glucose-dependent way, and each slows the emptying of the stomach.¹⁸ On the Mounjaro label, that slowing is largest after the first dose.¹

Only semaglutide comes as a tablet

Mounjaro is injection only: single-dose pens, single-dose vials, multi-dose vials and KwikPens.¹ Semaglutide comes as both injections and tablets.⁹¹⁰ On the Wegovy label, 89% of an injected dose is absorbed, against about 1% to 2% of a tablet dose.⁹ Semaglutide tablets go up to 25 mg a day, while its weekly injections stay at 7.2 mg or less.⁹

What each is approved for

Mounjaro's label has two uses, both in type 2 diabetes: blood sugar control in adults and children 10 and older, and lowering the risk of major cardiovascular events in high-risk adults.¹ Weight loss is not one of them.¹ Eli Lilly sells tirzepatide for long-term weight reduction under a second brand, Zepbound.⁷

Semaglutide's uses are spread across its brands. Ozempic injection covers blood sugar control in type 2 diabetes, with heart and kidney risk indications.⁸ Rybelsus and Ozempic tablets cover blood sugar control and heart risk in type 2 diabetes.¹⁰ Wegovy covers weight reduction, heart risk in adults with established cardiovascular disease and obesity or overweight, and the liver disease MASH.⁹

Head-to-head trials

Two large trials compared the molecules directly. In SURPASS-2, as summarized on the Mounjaro label, 1,879 adults with type 2 diabetes on metformin took tirzepatide 5, 10 or 15 mg or semaglutide 1 mg weekly for 40 weeks.¹ HbA1c fell 2.0, 2.2 and 2.3 points on tirzepatide against 1.9 on semaglutide, and the label's table marks all three differences as statistically significant.¹ Weight fell 7.6, 9.3 and 11.2 kg against 5.7 kg.¹

SURMOUNT-5, an open-label trial, tested weight in 751 adults with obesity but without type 2 diabetes. Each person received the maximum tolerated weekly dose, 10 or 15 mg of tirzepatide or 1.7 or 2.4 mg of semaglutide, for 72 weeks.¹³¹² Mean weight change was -20.2% on tirzepatide and -13.7% on semaglutide.¹²

SURPASS-2 matched Mounjaro's diabetes use. SURMOUNT-5 tested tirzepatide for weight, which is Zepbound's use rather than Mounjaro's.¹⁷ Neither trial used semaglutide's highest approved injected dose, now 7.2 mg weekly.⁹

Heart outcome trials

Both molecules carry heart indications, earned in trials of different design. Mounjaro's SURPASS-CVOT followed 13,299 adults with type 2 diabetes and established cardiovascular disease for a median of 210.1 weeks, against dulaglutide, another GLP-1 receptor agonist approved to lower heart risk.¹ A first major heart event occurred in 12.1% on Mounjaro against 13.0% on dulaglutide.¹ The label calls Mounjaro non-inferior to dulaglutide and says superiority was not established.¹ Death from any cause was 8.5% against 10.1%, a result the label says was not controlled for multiple testing.¹

Semaglutide's three heart indications are each backed by a placebo-controlled trial. The hazard ratios for major heart events were 0.74 for Ozempic in SUSTAIN 6, 0.80 for Wegovy in SELECT, and 0.86 for Rybelsus in a trial of 9,650 adults.⁸⁹¹⁴¹⁰ A hazard ratio below 1 means fewer events than on placebo. Because one drug was measured against another active drug and the others against placebo, the results cannot be ranked against each other.

Dosing and side effects

The milligram scales are not comparable. Mounjaro runs from 2.5 mg to 15 mg weekly; injected semaglutide runs from 0.25 mg up to 7.2 mg weekly, depending on the brand.¹⁹ On every one of these labels the dose starts low and climbs in steps to reduce stomach and gut side effects; each step is the prescriber's call.¹⁸⁹¹⁰

Stomach and gut effects are the most common side effects on both sides.¹⁸ On the Mounjaro label, nausea affected 12% to 18% on 5 to 15 mg against 4% on placebo, and most of it occurred while the dose was being raised.¹ About half of adults in seven Mounjaro trials (51%) developed antibodies to tirzepatide.¹ No clinically significant effect on drug levels or effectiveness was found, but allergic and injection site reactions were more common in people with antibodies.¹

Both molecules carry a boxed warning for thyroid C-cell tumors seen in rodents.¹⁸ Labels on both sides rule out use with a personal or family history of medullary thyroid carcinoma or with MEN 2.¹⁸

Which page to read next

Start with the Mounjaro profile and the semaglutide profile. The tirzepatide profile covers Mounjaro's ingredient across both of its brands, and Mounjaro vs tirzepatide explains that brand and ingredient pair. For brand against brand, see Mounjaro vs Ozempic and Mounjaro vs Wegovy. The drug class as a whole is introduced on What is GLP-1?, and the GLP-1 comparisons page lists every pair.