Compound Names

What Is Tirzepatide?

Published May 2, 2026 · Updated Sep 12, 2026 · 8 minute read

Tirzepatide is a once-weekly injectable peptide that activates two incretin receptors, GIP and GLP-1. Eli Lilly sells it as Mounjaro for type 2 diabetes and as Zepbound for weight reduction and sleep apnea. This page is about the molecule: what it does, what its trials showed, and what both labels say.

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Key Takeaways

  • Tirzepatide activates two incretin receptors, GIP and GLP-1, from a single 39-amino-acid peptide injected once weekly.
  • In SURMOUNT-1, 15 mg produced 20.9% mean weight loss over 72 weeks against 3.1% on placebo. In SURPASS-2 it beat semaglutide 1 mg on HbA1c and weight.
  • Outcomes evidence: SURPASS-CVOT showed non-inferiority to dulaglutide for major cardiovascular events in type 2 diabetes; SUMMIT cut cardiovascular death or worsening heart failure in HFpEF with obesity; SURMOUNT-OSA cut the apnea-hypopnea index.
  • Half-life is about 5 days, steady state takes about 4 weeks, and a missed dose can be taken within 4 days.
  • Both labels share the thyroid C-cell boxed warning, the same GI, pancreatitis, and gallbladder warnings, and an oral-contraceptive precaution semaglutide does not have.
Tirzepatide
Receptors GIP and GLP-1
Structure 39-amino-acid peptide based on the GIP sequence, with a C20 fatty diacid for albumin binding
Dosing 2.5 to 15 mg subcutaneously once weekly, 2.5 mg steps at least 4 weeks apart
Half-life About 5 days; steady state after about 4 weeks
Missed dose Within 4 days; otherwise skip
Brands Mounjaro (type 2 diabetes, cardiovascular risk reduction); Zepbound (weight reduction, obstructive sleep apnea)
First approved 2022 (Mounjaro); Zepbound 2023
Maker Eli Lilly

1. What the Two Receptors Do

GLP-1 and GIP are the two incretins, gut hormones released after a meal that raise insulin when glucose is high. GLP-1 receptor agonists such as semaglutide also slow gastric emptying and reduce appetite. Tirzepatide adds GIP receptor activity to that. On its own, GIP agonism does little for weight; paired with GLP-1 agonism it appears to add appetite suppression and to blunt nausea at a given level of effect, which is the leading explanation for why tirzepatide reaches a larger effect at tolerable doses. The mechanism is still being worked out; what is GIP covers the open questions.

The peptide is built on the GIP backbone with substitutions that let it bind both receptors, plus a fatty-acid chain that binds albumin and stretches the half-life to about 5 days, long enough for weekly injection.

2. Weight Loss

The pivotal obesity trial was SURMOUNT-1: 2,539 adults with obesity or overweight and no diabetes, randomised to 5, 10, or 15 mg or placebo for 72 weeks.

20.9%mean weight loss on 15 mg at 72 weeks, against 3.1% on placebo. 5 mg produced 15.0% and 10 mg 19.5%.
57%of the 15 mg group lost at least 20% of their body weight, versus 3% on placebo.
20.2% vs 13.7%tirzepatide versus semaglutide 2.4 mg at 72 weeks in SURMOUNT-5, the head-to-head in 751 adults with obesity.

Two follow-on trials matter for interpretation. SURMOUNT-4 withdrew the drug after 36 weeks: participants switched to placebo regained 14.0% from week 36 to week 88, while those who continued lost a further 5.5%, and 89.5% of continuers kept at least 80% of their loss against 16.6% on placebo. The SURMOUNT-1 DXA substudy of 160 participants found that about 75% of weight lost was fat and 25% lean mass, the same split as placebo. The muscle loss page covers what that does and does not mean.

3. Blood Sugar

SURPASS-2 is the head-to-head in type 2 diabetes: 1,879 adults on metformin randomised to tirzepatide 5, 10, or 15 mg or semaglutide 1 mg for 40 weeks. From a baseline HbA1c of 8.28%, tirzepatide lowered it by 2.01, 2.24, and 2.30 percentage points against 1.86 for semaglutide; every dose was non-inferior and then superior. Weight fell 7.6, 9.3, and 11.2 kg against 5.7 kg. Nausea ran 17% to 22% on tirzepatide and 18% on semaglutide; clinically significant hypoglycemia was 0.2% to 1.7% versus 0.4%. The Ozempic vs Mounjaro page has the charts.

4. Outcomes Trials

Weight and HbA1c are surrogates. Three trials have measured harder endpoints.

Trial Population Comparator Result
SURPASS-CVOT, n=13,299 Type 2 diabetes with cardiovascular disease Dulaglutide Major cardiovascular events 12.2% vs 13.1%, HR 0.92, non-inferior
SUMMIT, n=731 Heart failure with preserved ejection fraction and obesity Placebo Cardiovascular death or worsening heart failure 9.9% vs 15.3%, HR 0.62
SURMOUNT-OSA, two 52-week trials Moderate to severe obstructive sleep apnea and obesity Placebo Apnea-hypopnea index down 25.3 vs 5.3 events per hour without PAP; 29.3 vs 5.5 with PAP

SURPASS-CVOT tested tirzepatide against dulaglutide, itself a drug shown to reduce cardiovascular events, so it establishes that tirzepatide is at least as good, not how much better than nothing it is. It gave Mounjaro a cardiovascular risk-reduction indication in August 2026. SUMMIT is placebo-controlled but measured heart failure events, a different outcome from heart attack and stroke, and is not on any label. SURMOUNT-OSA made Zepbound the first drug approved for obstructive sleep apnea. The placebo-controlled cardiovascular trial in obesity, SURMOUNT-MMO, has not reported.

5. Pharmacokinetics and Dosing

Value, from the labels
Half-life About 5 days
Time to steady state About 4 weeks of weekly dosing
Largely cleared after last dose Roughly 3.5 to 4 weeks (five half-lives)
Starting dose 2.5 mg weekly for 4 weeks, tolerability only
Steps 5, 7.5, 10, 12.5, 15 mg, each held at least 4 weeks
Maximum 15 mg in adults; 10 mg for Mounjaro in children 10 to 17
Missed dose Take within 4 days (96 hours); otherwise skip. Never two doses within 3 days

The milligrams are not comparable with semaglutide’s. A 5 mg tirzepatide dose and a 1 mg semaglutide dose are different molecules at different potencies, and no label offers a conversion. The titration schedule generator builds the dated ladder, and the half-life visualizer plots the curve.

6. Safety Sections Shared by Both Labels

Mounjaro and Zepbound carry the same boxed warning on thyroid C-cell tumors, seen in rats, with a contraindication for a personal or family history of medullary thyroid carcinoma or MEN 2. Both warn on acute pancreatitis, severe gastrointestinal reactions, acute kidney injury from dehydration, acute gallbladder disease, hypoglycemia with insulin or a sulfonylurea, diabetic retinopathy complications in people with type 2 diabetes, hypersensitivity, and pulmonary aspiration under anesthesia. The most common adverse reactions on the Mounjaro label are nausea, diarrhea, decreased appetite, vomiting, constipation, dyspepsia, and abdominal pain, mostly during dose escalation.

One item is specific to tirzepatide within this class: the labels tell people using oral hormonal contraceptives to switch to a non-oral method or add a barrier method for 4 weeks after starting and after each dose increase, because delayed gastric emptying can reduce absorption of the pill. Semaglutide’s labels have no such instruction.

7. Where the Brand Pages Take Over

For the log, the entry is the same whichever box the pen came in: product, date, milligrams, and injection site. Everything that depends on the label lives on the brand pages: Mounjaro for the diabetes and cardiovascular indications, devices, and pediatric ceiling; Zepbound for weight reduction and sleep apnea. For comparisons, see semaglutide vs tirzepatide, Wegovy vs Zepbound, and retatrutide vs tirzepatide for the triple agonist that comes next.

8. Tirzepatide FAQ

  • Is tirzepatide a GLP-1?

    Partly. It is a GIP receptor and GLP-1 receptor agonist: one molecule that activates both incretin receptors. The FDA labels call it a GIP/GLP-1 receptor agonist rather than a GLP-1 receptor agonist, though it is grouped with the GLP-1 class in most discussion.

  • How much weight loss does tirzepatide produce?

    In SURMOUNT-1, adults with obesity and no diabetes lost 15.0%, 19.5%, and 20.9% of body weight on 5, 10, and 15 mg over 72 weeks, against 3.1% on placebo. In SURMOUNT-5, tirzepatide at 10 or 15 mg produced 20.2% versus 13.7% for semaglutide 2.4 mg. In people with type 2 diabetes the numbers are smaller: 7.6 to 11.2 kg over 40 weeks in SURPASS-2.

  • Does tirzepatide reduce heart attacks and strokes?

    In SURPASS-CVOT, adults with type 2 diabetes and cardiovascular disease had major events at 12.2% on tirzepatide versus 13.1% on dulaglutide, hazard ratio 0.92, which met non-inferiority. That earned Mounjaro a cardiovascular indication in August 2026. No placebo-controlled trial of heart attack and stroke has reported; SUMMIT, the one placebo-controlled cardiovascular trial, measured heart failure outcomes.

  • How long does tirzepatide stay in the body?

    The half-life is about 5 days, so levels fall to a few percent of steady state roughly 3.5 to 4 weeks after the last dose. Steady state is reached after about 4 weeks of weekly dosing.

  • What is the difference between Mounjaro and Zepbound?

    The molecule, doses, and devices are the same. Mounjaro's label covers type 2 diabetes and cardiovascular risk reduction in type 2 diabetes; Zepbound's covers weight reduction and obstructive sleep apnea in adults with obesity. The Zepbound vs Mounjaro page sets the two labels side by side.

9. Sources

References used for this article

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