One molecule, two medicinesEvery FDA-approved tirzepatide product is made by Eli Lilly and sold as Mounjaro or Zepbound.[4][3] Products sold as “tirzepatide peptide” for research, or made by compounders, are not those medicines; see the last section.
What is tirzepatide?
Tirzepatide is a once-weekly injectable medicine that the FDA label defines as “a GIP receptor and GLP-1 receptor agonist.”[1] GIP and GLP-1 are two gut hormones released after eating; tirzepatide switches on the receptors for both. It was first approved on May 13, 2022 as Mounjaro for type 2 diabetes, and on November 8, 2023 as Zepbound for weight management.[4][3]
Tirzepatide peptide structure
Chemically, tirzepatide is a modified peptide based on the GIP sequence, with a long fatty-acid chain attached so it lasts a week in the body.[1]
| Feature | What the label says |
|---|---|
| Backbone | Based on the GIP (glucose-dependent insulinotropic polypeptide) sequence |
| Modified amino acids | Aminoisobutyric acid (Aib) at positions 2 and 13 |
| End of the chain | C-terminal amide |
| Side chain | Lysine at position 20 linked to a C20 fatty diacid (1,20-eicosanedioic acid) |
| Molecular weight | 4,813.53 Da |
| Formula | C225H348N48O68 |
The label says the C20 fatty diacid “enables albumin binding and prolongs the half-life,” which is why tirzepatide lasts about 5 days (Mounjaro label) or 5 to 6 days (Zepbound label) and is injected once a week.[1]
How does tirzepatide work?
Tirzepatide works mainly by reducing appetite and calorie intake, and in diabetes by improving how the body handles glucose. The label's pharmacology sections list these effects:[1]
- Appetite: GLP-1 is “a physiological regulator of appetite and caloric intake,” and nonclinical studies suggest GIP may add to that. Both receptors sit in brain areas that regulate appetite.
- Calories and body composition: tirzepatide decreases calorie intake and lowers body weight “with greater fat mass loss than lean mass loss.”
- Blood sugar: it raises insulin release only when glucose is high, lowers glucagon, and increased insulin sensitivity in a 28-week study in type 2 diabetes.
- Stomach emptying: it slows gastric emptying, most after the first dose, with the effect fading over time.
Is tirzepatide a GLP-1?
Yes, and more: tirzepatide is a GLP-1 receptor agonist that is also a GIP receptor agonist, so it is often called a dual agonist.[1] Semaglutide (Ozempic, Wegovy) acts on the GLP-1 receptor only. In the head-to-head SURMOUNT-5 trial, average weight change was −20.2% with tirzepatide versus −13.7% with semaglutide over 72 weeks.[5] More on tirzepatide vs semaglutide.
Tirzepatide brand names
In the United States tirzepatide has two brand names, both from Eli Lilly, with different approved uses.[2][1]
| Brand | First approved | Approved for | Forms |
|---|---|---|---|
| Mounjaro[4] | May 13, 2022 | Type 2 diabetes (adults and children 10+); cardiovascular risk reduction in type 2 diabetes | Single-dose pen and vial, KwikPen, multi-dose vial |
| Zepbound[3] | November 8, 2023 | Chronic weight management; moderate to severe sleep apnea with obesity | Single-dose pen and vial, KwikPen, multi-dose vial |
The two contain the same molecule at the same strengths; their labels differ on uses and a few dosing details, compared on Zepbound vs Mounjaro.
Tirzepatide injection: how it is given
Tirzepatide is injected under the skin once a week, at any time of day, with or without meals, into the abdomen, thigh or back of the upper arm.[1] About 80% of the dose reaches the bloodstream, peaking at a median of 24 hours.[1] Doses run from 2.5 mg to 15 mg in 2.5 mg steps; see the tirzepatide dosage chart and Zepbound injection sites.
“Research peptide” tirzepatide is not the medicine
Tirzepatide sold as a research peptide or powder is not an approved medicine, and the FDA has warned companies selling it labeled “for research purposes” or “not for human consumption.”[6] The FDA also says compounded versions are not reviewed for safety, effectiveness or quality.[6] Details: compounded tirzepatide and tirzepatide pills.
Related
- What is Zepbound?The weight-management brand
- Tirzepatide side effectsBoth labels
- Tirzepatide dosage calculatormg to units
Frequently asked questions
What is tirzepatide?
How does tirzepatide work?
It activates GIP and GLP-1 receptors, which lowers appetite and calorie intake, slows stomach emptying, and improves insulin release and sensitivity.[1]
Is tirzepatide a peptide?
Yes. It is a modified peptide based on the GIP hormone sequence, with a fatty-acid side chain, and a molecular weight of 4,813.53 Da.[1]
Sources
- Zepbound (tirzepatide) injection: prescribing information, Medication Guide and Instructions for Use
- Mounjaro (tirzepatide) injection: prescribing information and Instructions for Use
- Drugs@FDA: NDA 217806 (Zepbound) approval history and supplement letters
- Drugs@FDA: NDA 215866 (Mounjaro) approval history and supplement letters
- Aronne LJ et al. Tirzepatide as compared with semaglutide for the treatment of obesity (SURMOUNT-5)
- FDA's concerns with unapproved GLP-1 drugs used for weight loss