What is Mounjaro?

What sources report

Mounjaro was the first tirzepatide product approved in the US: FDA approved it in May 2022 as a new molecular entity.² It is a clear, colorless to slightly yellow solution that comes ready to inject from a prefilled pen or a vial, once a week.¹ Eli Lilly also sells the same active ingredient as Zepbound, which carries different approved uses: weight reduction and obstructive sleep apnea.⁴⁵ The molecule itself, its chemistry and its wider research record are covered in What is Tirzepatide?.

How it works

Tirzepatide is a dual agonist. It binds to and activates both the GIP receptor and the GLP-1 receptor, the targets of the natural hormones GIP and GLP-1.¹ Semaglutide, the active ingredient of Ozempic, activates the GLP-1 receptor alone.¹² Dulaglutide, the comparator in Mounjaro's heart outcomes trial, is also a GLP-1 receptor agonist.¹ According to the label, tirzepatide boosts insulin release and lowers glucagon, both in a glucose-dependent way, and it delays stomach emptying.¹

The peptide is built on the sequence of the GIP hormone.¹ It carries aminoisobutyric acid at positions 2 and 13, an amidated end, and a C20 fatty diacid attached at lysine 20.¹ That fatty chain binds albumin in the blood, which stretches the half-life to about 5 days and allows once-weekly dosing.¹ The label gives a molecular weight of 4813.53 Da and the formula C225H348N48O68.¹

What the trials found

In five SURPASS trials of adults with type 2 diabetes, lasting 40 to 52 weeks, average HbA1c fell about 1.7 to 2.4 points on 5 to 15 mg, and average weight fell about 5.4 to 11.3 kg.¹ SURPASS-CVOT followed 13,299 adults with type 2 diabetes and heart or blood vessel disease for a median of 210.1 weeks.¹ A first heart attack, stroke or cardiovascular death occurred in 12.1% on Mounjaro and 13.0% on dulaglutide: non-inferior, but not shown to be superior.¹ Full summary with evidence levels: Mounjaro benefits and uses. The goal pages go deeper on Mounjaro and blood sugar and Mounjaro and weight loss.

How it compares

Side-by-side pages set Mounjaro next to other GLP-1 medicines: Mounjaro vs Ozempic, Mounjaro vs Wegovy, Mounjaro vs Semaglutide, GLP-1 vs Mounjaro and Mounjaro vs Tirzepatide. The drug class as a whole is introduced in What is GLP-1?.

Side effects

Stomach and gut effects lead the label: in pooled placebo-controlled trials, nausea affected 12% to 18% of adults on 5 to 15 mg against 4% on placebo, and diarrhea 12% to 17% against 9%, mostly while the dose was being raised.¹ The boxed warning covers thyroid C-cell tumors that tirzepatide caused in rats; whether it causes them in humans is unknown.¹ The label contraindicates it in people with a personal or family history of medullary thyroid carcinoma or MEN 2.¹ The label also warns of pancreatitis, low blood sugar when combined with insulin or a sulfonylurea, kidney injury from dehydration, gallbladder disease and serious allergic reactions.¹ Full list: Mounjaro side effects.

Dosage information

The label starts Mounjaro at 2.5 mg once weekly and, if more blood sugar control is needed, raises it in 2.5 mg steps after at least 4 weeks on each dose.¹ The maximum is 15 mg once weekly for adults and 10 mg once weekly for children 10 and older.¹ Since August 2026, the label also allows 2.5 mg to be continued for ongoing blood sugar control.³ The prescriber sets and adjusts the dose. Full schedule: Mounjaro dosage.

How it is used

Mounjaro comes ready to inject as a single-dose pen, a single-dose vial, a multi-dose vial or a KwikPen, and none of their instructions include a mixing step.¹ It is injected under the skin of the abdomen or thigh, or the back of the upper arm when another person gives it, once a week at any time of day, with a new spot each week.¹ A healthcare provider trains the patient or caregiver on the exact presentation before the first dose.¹ Unopened pens and vials are kept in the refrigerator at 36°F to 46°F (2°C to 8°C) and are never frozen.¹ Step by step, by presentation: Mounjaro injection sites and pen use.

Regulatory status

Mounjaro is approved under NDA 215866, held by Eli Lilly, and Drugs@FDA lists every Mounjaro product as a prescription drug.²

• May 13, 2022. First approval, as a new molecular entity under priority review, for blood sugar control in adults with type 2 diabetes.²¹
• December 19, 2025. The blood sugar use was extended to children 10 and older with type 2 diabetes.²¹
• August 27, 2026. FDA added a second use: lowering the risk of cardiovascular death, non-fatal heart attack or non-fatal stroke in high-risk adults with type 2 diabetes, based on SURPASS-CVOT.³ A companion change allowed 2.5 mg to be used for ongoing blood sugar control.³

Weight loss is not a US indication for Mounjaro.¹ FDA approved the same molecule for weight reduction under the Zepbound name.⁴ In the European Union, Mounjaro was authorized on September 15, 2022.⁶ Its EU uses also include helping adults lose weight and keep it under control, alongside diet and physical activity.⁷ As in the US, it is available there only on prescription.⁸

Anti-doping: GLP-1 receptor agonists, tirzepatide among them, are not on the WADA Prohibited List, and WADA kept their status unchanged for 2027 while it gathers more data.⁹

Compounded and research-labeled tirzepatide

Compounded drugs are not FDA approved.¹¹ FDA declared the tirzepatide shortage resolved on December 19, 2024.¹⁰ It gave compounding pharmacies until February 18, 2025, and outsourcing facilities until March 19, 2025, to stop making copies tied to the shortage.¹⁰ As of May 31, 2026, FDA had received more than 730 adverse event reports linked to compounded tirzepatide.¹¹ FDA has also warned companies selling unapproved tirzepatide falsely labeled "for research purposes" or "not for human consumption".¹¹ It says unapproved versions do not undergo FDA review for safety, effectiveness and quality before they are marketed.¹¹ None of them is Mounjaro, which is the approved, prescription-only product.²