Tirzepatide: the dual-hormone drug behind Mounjaro and Zepbound

In its main obesity trial, tirzepatide cut body weight by about 21% on the top dose, and head to head it beat semaglutide. It's also a little confusing, because it goes by two names. Mounjaro and Zepbound are the same molecule, from the same company, in separately labeled formulations and devices. What differs is the label, and the label decides who it's approved for and what it costs.

Tirzepatide acts on two hormone receptors, not one

Tirzepatide activates both the GIP and GLP-1 receptors, the targets of two hormones your gut releases after you eat. The label says it “selectively binds to and activates both the GIP and GLP-1 receptors,” and a fatty-acid chain lets it bind to albumin in the blood, with an elimination half-life supporting the approved weekly schedule ^[1].

1. Insulin when blood sugar is high. It boosts insulin release in a glucose-dependent way and lowers glucagon ^[2].
2. Better insulin sensitivity. In a clamp study after 28 weeks, tirzepatide made the body respond better to insulin.
3. Slower stomach emptying. The labeled delay is largest after the first dose and diminishes over time; this does not mean all digestive symptoms disappear.
4. Less appetite. GLP-1 is a regulator of appetite, and nonclinical studies suggest GIP adds to that effect ^[1].

Is tirzepatide a GLP-1? Partly. It's a GLP-1 receptor agonist and a GIP receptor agonist in one molecule. That second action is what sets it apart from semaglutide, which acts on GLP-1 alone.

Mounjaro and Zepbound are the same drug with different labels

Mounjaro and Zepbound both contain tirzepatide, made by Eli Lilly, with distinct labels, presentations and administration instructions. Mounjaro is labeled for type 2 diabetes. Zepbound is labeled for weight and sleep apnea. Is tirzepatide the same as Zepbound, or as Mounjaro? It's the ingredient in both.

What is tirzepatide's brand name? It has two, and you now know which is which. Our Zepbound vs Mounjaro comparison goes through coverage, price and the off-label question in more detail.

Tirzepatide is approved for diabetes, heart risk in diabetes, weight and sleep apnea

Across its two brands, tirzepatide is approved for four uses. Mounjaro covers blood sugar control in type 2 diabetes for adults and children 10 and older, and lowering the risk of heart attack, stroke and cardiovascular death in adults with type 2 diabetes at high risk ^[2]. Zepbound covers weight reduction and maintenance in adults with obesity or overweight plus a related condition, and moderate to severe sleep apnea in adults with obesity ^[1].

The heart-risk approval rests on SURPASS-CVOT, which tested tirzepatide against dulaglutide, an older GLP-1 drug already shown to lower heart events, in 13,299 randomized adults with type 2 diabetes and atherosclerotic cardiovascular disease. After134ineligibleparticipants were excluded, 13,165 formed the modified intention-to-treat population. First composite cardiovascular events occurred in 12.2% versus 13.1% on dulaglutide: HR 0.92 (95.3% CI 0.83–1.01). This met the prespecified noninferiority criterion, not superiority; it does not prove identical risk or absence of harm ^[17]. The same data were added to Zepbound's label in August 2026 as information, not a new use.

The trials showed 15% to 21% weight loss and a head-to-head win over semaglutide

In SURMOUNT-1, adults with obesity and no diabetes lost 15.0%, 19.5% and 20.9% of their weight on 5, 10 and 15 mg over 72 weeks, against 3.1% on placebo ^[12]. About half of people on 10 or 15 mg lost at least 20%.

SURMOUNT-4 enrolled 783 adults into an open-label lead-in; 670 completed it and were randomized after 36 weeks at maximum tolerated 10/15 mg. These selected randomized participants had lost 20.9% from original baseline. From week 36 to 88, weight changed +14.0% on placebo versus −5.5% with continuation ^[14]. The week 36 denominator matters: a 14% increase after earlier weight loss is not 14 percentage points of original weight. At week 88, mean weight remained 9.9% below original baseline on placebo versus 25.3% below with continuation. These selected-group averages do not predict an individual’s result.

The sleep-apnea evidence addresses a distinct condition. In SURMOUNT-OSA, breathing interruptions fell by 25.3 events an hour on tirzepatide vs 5.3 on placebo in trial1 participants not receiving PAP at baseline, and by 29.3 vs 5.5 in trial2 participants receiving PAP at baseline ^[15]. That's what FDA based Zepbound's sleep apnea approval on.

Tirzepatide causes weight loss by cutting appetite and calorie intake

Tirzepatide leads to weight loss because people eat less. The Zepbound label says it “decreases calorie intake,” that “the effects are likely mediated by affecting appetite,” and that it “lowers body weight with greater fat mass loss than lean mass loss” ^[1]. Both GIP and GLP-1 receptors sit in brain areas that control appetite, and in animal studies tirzepatide reached and activated those areas.

Does tirzepatide burn fat? The label doesn't describe a fat-burning action. Fat comes off because calorie intake falls, with some lean mass lost too, as in any large weight loss. The label’s nonclinical GIP findings are not a causal allocation of the head-to-head weight difference. SURMOUNT-5 compared specified regimens; it does not prove a receptor-count rule that ranks every medicine or dose.

How does Mounjaro work for weight loss, then? The same way. Mounjaro's label notes that tirzepatide “decreases food intake, and reduces body weight” in people with type 2 diabetes ^[2], even though weight isn't its approved use.

Who tirzepatide is for, and who the label rules out

For weight, the Zepbound trials enrolled adults with a BMI of 30 or more, or 27 or more with a weight-related condition such as high blood pressure, abnormal cholesterol, sleep apnea or heart disease ^[1]. For diabetes, Mounjaro is for adults and children 10 and older with type 2 diabetes.

Both labels rule tirzepatide out for anyone with a personal or family history of medullary thyroid carcinoma or MEN 2, and serious allergy to tirzepatide or the product’s ingredients is another contraindication. The human relevance of rodent thyroid tumors is unknown. The Zepbound label says it may cause fetal harm, and both labels advise switching from birth-control pills to another method, or adding a barrier method, for four weeks after starting and after each dose increase. Your prescriber will also ask about pancreatitis, gallbladder problems and severe gastroparesis before writing it.

What the trials haven't answered yet

Some questions matter more to a longevity reader than to a diabetes clinic, and the trials don't settle them. The cited weight, glucose, apnea and cardiovascular trials do not establish that tirzepatide extends lifespan. The heart-risk approval covers only adults with type 2 diabetes at high risk, and it rests on a comparison with another GLP-1 drug, not placebo ^[17].

Lean mass is the other open question. The label says more fat than lean mass is lost, but it doesn't say how much lean mass older adults can afford to lose, or what happens to muscle over years of treatment. If you're over 60, ask your prescriber how they'll protect strength, with protein and resistance training, while you're on it.

Digestive effects are common; timing and serious warnings need context

Common labeled reactions include nausea, diarrhea, vomiting, constipation and other gastrointestinal symptoms. The Zepbound label specifically describes nausea, vomiting and diarrhea as occurring mostly during escalation and decreasing over time; that statement should not be generalized to every symptom or patient. In SURMOUNT-1, side effects led 4.3% to 7.1% of people to stop, against 2.6% on placebo ^[12]. Both brands carry a boxed warning about thyroid C-cell tumors seen in rodents.

The labels also warn about severe stomach reactions, kidney injury from dehydration, gallbladder disease, pancreatitis, allergic reactions, low blood sugar with insulin or sulfonylureas, diabetic eye complications and aspiration during anesthesia. Severe or persistent abdominal symptoms, repeated vomiting or dehydration warrant prompt clinical assessment. Tell the anesthesia team about treatment before a procedure. The fuller discussion, by brand and dose, is in our tirzepatide side effects guide.

There is no approved tirzepatide pill

No tirzepatide tablet is approved. Some online sellers offer compounded oral tirzepatide drops or tablets, but the approved injection trials do not establish the absorption, effectiveness or safety of the exact compounded oral preparation. Lilly's GLP-1 pill, Foundayo, contains a different drug, orforglipron, which acts on GLP-1 receptors only and is taken daily ^[3].

Is orforglipron the same as tirzepatide? No. Different molecule, different receptors, different form. They share a maker and a goal, and that's it.

Compounded tirzepatide isn't FDA-approved and is legal only in narrow cases

Compounded tirzepatide is a pharmacy-made version. It isn't FDA-approved, FDA does not review the compounded product for safety, effectiveness or quality before marketing ^[9]. FDA first determined the shortage resolved in October 2024 and reaffirmed that decision on December 19, 2024. Its transition policies differed for section 503A and section 503B compounders ^[8]. FDA reports more than 730 adverse-event reports associated with compounded tirzepatide through May 31, 2026; these do not establish causality, incidence or comparative risk ^[9].

An online offer and prescription alone do not establish compliance with the distinct patient-specific and outsourcing-facility requirements. Our guides explain whether compounded tirzepatide is still available, whether it works, whether it's safe and how it compares with Zepbound. The basics are on the compounded tirzepatide page.

Tirzepatide beat semaglutide head to head; retatrutide is still in trials

Against semaglutide, tirzepatide produced more weight loss in SURMOUNT-5 and a larger A1C drop in the open-label SURPASS-2 comparison of tirzepatide 5/10/15 mg with semaglutide 1 mg, in trials funded by Lilly ^{[13] [16]}. Our semaglutide vs tirzepatide comparison walks through both.

Retatrutide, Lilly's next drug, adds a third receptor, glucagon. It isn't FDA-approved for any use and can't legally be compounded. Read where retatrutide stands with FDA and the investigational comparison in retatrutide vs tirzepatide.

LillyDirect offers depend on product, dose, supply and eligibility

Zepbound lists $299 per 28-day supply at 2.5 mg, $399 at 5 mg and $449 at higher doses through LillyDirect if you refill within 45 days, or $499 to $699 if you don't ^[10]. Mounjaro is listed “starting at $499/month” for every strength ^[11]. These are different product offers; the cited price pages do not establish the manufacturer’s reason for the price difference.

A compounded offer needs a product-specific written quote, including clinical charges, dose assumptions, the supply and renewal interval. The Brightmeds review and Bionomy review explain distinct care and billing models; neither proves equivalence to a branded injection. Use the cost calculator to distinguish a payment schedule from an annualized comparison. Four-week supply does not itself prove four-week billing.

For the details, read what compounded tirzepatide costs, or compare every program on the compounded tirzepatide board. If a program pitches very small doses, our guide to microdosing tirzepatide explains what hasn't been tested.

Every form of tirzepatide needs a prescription

Brand or compounded, tirzepatide needs a prescription. Your own clinician can send a Zepbound or Mounjaro prescription to LillyDirect Pharmacy or a local pharmacy. Telehealth programs prescribe both brand and compounded versions after an online intake and a clinician review.