Tirzepatide
Tirzepatide switches on two gut-hormone receptors, GIP and GLP-1. It is a weekly injection approved for weight management under the brand Zepbound.
Brand names: Zepbound, Mounjaro
Tirzepatide (known as Mounjaro, Zepbound, formerly LY3298176)
Also searched as: tirzepitide, terzepatide, tirz, GLP-1 GIP shot.
Educational information. This page does not give dosing instructions or tell you what to take. Ask a prescriber about your own care.
In plain English
Tirzepatide is a lab-made molecule that activates two receptors your gut hormones normally use, one for GLP-1 and one for GIP. Both are released after meals and help control blood sugar and appetite.
Zepbound is the brand approved for weight management. Mounjaro is the brand approved for type 2 diabetes. Both are weekly injections.
Brand names and products
A generic name identifies the drug itself. A brand name identifies one company's product. One drug can come in several products with different forms and approved uses, so the brand name often tells you more about what a prescription is for.
| Brand name | Maker | Form | U.S. approved use | Status |
|---|---|---|---|---|
| Zepbound | Eli Lilly | Weekly injection | Weight management | FDA-approved for weight management |
| Mounjaro | Eli Lilly | Weekly injection | Type 2 diabetes | FDA-approved, but not for obesity |
Approved and investigational. Each product above is approved only for the use shown. A product approved for type 2 diabetes is not approved for weight management. This page covers approved products. Other uses and forms of tirzepatide may be under study. This atlas has not recorded them, so none are described here.
How it works
Tirzepatide is a single molecule that activates both the GIP receptor and the GLP-1 receptor. The GLP-1 part shares the appetite and gastric-emptying effects of other GLP-1 medicines. The added contribution of GIP receptor activation is still being studied.
Forms and approval status
| Form | How it is taken | U.S. status |
|---|---|---|
| Tirzepatide injection (Zepbound) | Once weekly. Weekly injection. Follow the label and your prescriber for how to use it. | Approved in the U.S. for weight reduction in adults with obesity, or overweight plus a weight-related condition, and to treat moderate to severe obstructive sleep apnea in adults with obesity. Used with diet and activity. |
What the trials found
These are group averages from published trials in adults without diabetes unless stated. See how to read trial numbers before comparing.
SURMOUNT-1
Average change in body weight. Every bar uses one scale, 0 to 25 percent.
- People studied
- 2,539 adults with obesity, or overweight plus at least one weight-related complication, without diabetes
- Length
- 72 weeks
- Compared with
- Placebo, including a 20-week dose-escalation period
- What was measured
- Average change in body weight at week 72
- Analysis approach
- Treatment-regimen estimand: effects regardless of treatment discontinuation
- Other results
- Weight loss of at least 5%: 85%, 89% and 91% across the three doses vs 35% with placebo. At least 20%: 50% (10 mg) and 57% (15 mg) vs 3%.
- Safety
- Most side effects were gastrointestinal, mostly mild to moderate, and mainly during dose escalation. Stopping treatment because of side effects: 4.3%, 7.1% and 6.2% across the three doses vs 2.6% with placebo.
- Limits
- Funded by the manufacturer. Participants did not have diabetes. Group averages do not predict one person's result.
Sources: Jastreboff AM 2022
SURMOUNT-5
Average change in body weight. Every bar uses one scale, 0 to 25 percent.
- People studied
- 751 adults with obesity but without type 2 diabetes
- Length
- 72 weeks
- Compared with
- Semaglutide, head to head. Open label, so participants and staff knew which drug was used. No placebo group.
- What was measured
- Average percent change in body weight at week 72
- Analysis approach
- Least-squares mean change from baseline to week 72, as reported in the abstract.
- Other results
- Waist circumference fell 18.4 cm with tirzepatide vs 13.0 cm with semaglutide. More people on tirzepatide reached weight loss of at least 10%, 15%, 20% and 25%.
- Safety
- Gastrointestinal effects were the most common side effects in both groups. Most were mild to moderate and happened mainly while the dose was being raised.
- Limits
- Funded by Eli Lilly, the maker of tirzepatide. Open label. Each person took the highest dose they could tolerate, so the doses were not identical across people. Group averages do not predict one person's result.
Sources: Aronne LJ 2025
Safety
Based on the FDA-approved label for Zepbound. The official label is the controlling source for warnings. The points below are a summary and may be incomplete.
Boxed warning and label notes
- Tirzepatide injection (Zepbound): Boxed warning: risk of thyroid C-cell tumors. In rats tirzepatide causes these tumors, and whether it does in humans, including medullary thyroid carcinoma, has not been determined. Not for people with a personal or family history of medullary thyroid carcinoma or MEN 2.
Warnings labels describe
- The Zepbound label carries a boxed warning: in rats tirzepatide causes thyroid C-cell tumors, and it is not known whether it does in humans. It is contraindicated with a personal or family history of medullary thyroid carcinoma or MEN 2, and after a serious allergic reaction to tirzepatide.
- The label's warnings and precautions list severe stomach and bowel reactions, kidney injury from dehydration, acute gallbladder disease, acute pancreatitis, allergic reactions, low blood sugar, diabetic retinopathy complications in people with type 2 diabetes, and aspiration during anesthesia or deep sedation.
- The label advises people who use oral hormonal birth control to switch to a non-oral method, or add a barrier method for 4 weeks after starting and for 4 weeks after each dose increase. Anyone using birth control pills should ask their prescriber.
- The label says to stop the medicine when pregnancy is recognized, because weight loss offers no benefit in pregnancy and may cause fetal harm. Anyone planning a pregnancy should talk to their prescriber.
- The label says using it with other tirzepatide products or any GLP-1 receptor agonist is not recommended.
Most common in trials
- Nausea
- Diarrhea
- Vomiting
- Constipation
- Abdominal pain
Less common but serious
- Pancreatitis
- Gallbladder problems
- Dehydration with kidney injury
- Severe allergic reactions
- Diabetic retinopathy complications in people with type 2 diabetes
What is still unknown
- How much of the effect comes from GIP receptor activation versus GLP-1 receptor activation.
- How much weight returns after stopping, and how that varies between people.
- How the head-to-head result holds up over longer periods. SURMOUNT-5 compared tirzepatide with semaglutide for 72 weeks, was open label and was paid for by the maker of tirzepatide.
Compiled from public information: FDA-approved labels, manufacturer websites, ClinicalTrials.gov and published journal articles. Sources are listed at the bottom of this page.
Sources
- Zepbound (tirzepatide) injection: prescribing information Eli Lilly and Company, on DailyMed (U.S. National Library of Medicine). Label version 8/2026. Official FDA label on DailyMed
- DailyMed: current FDA drug labels U.S. National Library of Medicine. Regulator
- Drugs@FDA: approved drug products U.S. Food and Drug Administration. Regulator
- Tirzepatide as compared with semaglutide for the treatment of obesity (SURMOUNT-5) Aronne LJ, et al. N Engl J Med. 2025;393(1):26-36. PMID 40353578. Funding: Eli Lilly. Journal article
- Mechanisms of action and therapeutic application of glucagon-like peptide-1 Drucker DJ. Cell Metab. 2018;27(4):740-756. PMID 29617641. Journal article
- Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1) Jastreboff AM, et al. N Engl J Med. 2022;387(3):205-216. PMID 35658024. Funding: Eli Lilly. Journal article
- Mounjaro (tirzepatide) injection: prescribing information Eli Lilly and Company, on DailyMed (U.S. National Library of Medicine). Label version 8/2026. Official FDA label on DailyMed