What Is Zepbound? How Tirzepatide Works, Who It's For and How Safe It Is

Zepbound is the brand name for tirzepatide, a once-weekly injection made by Eli Lilly that the FDA approved for chronic weight management on November 8, 2023.2 It is prescribed together with a reduced-calorie diet and increased physical activity.1

The current label lists two uses in adults:1

• to reduce excess body weight and maintain that reduction long term in adults with obesity, or with overweight plus at least one weight-related condition;
• to treat moderate to severe obstructive sleep apnea (OSA) in adults with obesity.

At approval, the FDA defined the weight population as adults with a BMI of 30 kg/m² or more, or 27 kg/m² or more with at least one weight-related condition.2

Zepbound is injected under the skin of the abdomen, thigh or back of the upper arm once a week, at any time of day, with or without meals.1 The full walk-through is in our guide on how to inject Zepbound.

Yes, and more: Zepbound activates two hormone receptors, GLP-1 and GIP, so the label calls it a "GIP receptor and GLP-1 receptor agonist."1 Most older drugs in the class, such as semaglutide, act on the GLP-1 receptor alone. For a side-by-side comparison of the two molecules, see tirzepatide vs semaglutide.

GLP-1 (glucagon-like peptide-1) and GIP (glucose-dependent insulinotropic polypeptide) are hormones released by the gut after eating. Tirzepatide binds to and activates the receptors for both.1

Zepbound lowers body weight mainly by reducing appetite and calorie intake, acting on receptors in brain areas that regulate hunger.1 The label states that GLP-1 is a physiological regulator of appetite and calorie intake, and that nonclinical studies suggest GIP may add to that effect.1

Three mechanisms are described in the prescribing information:1

• Appetite. Both GIP and GLP-1 receptors are found in brain regions involved in appetite, and tirzepatide decreases calorie intake.
• Stomach emptying. Tirzepatide slows gastric emptying. The effect is largest after the first dose and diminishes over time.
• Blood sugar. It stimulates insulin release when glucose is high and lowers glucagon.

The label also states that tirzepatide lowers body weight with greater fat mass loss than lean mass loss.1

In SURMOUNT-1, a 72-week trial of 2,539 adults with obesity or overweight and no diabetes, average weight loss was 15.0% on 5 mg, 19.5% on 10 mg and 20.9% on 15 mg, against 3.1% on placebo.5,1 In a second 72-week trial in adults with type 2 diabetes, average loss was 12.8% on 10 mg and 14.7% on 15 mg, against 3.2% on placebo.1 All participants also received diet and exercise counseling.1

Dose matters, but so does tolerability. Our Zepbound dosage guide covers the step-up schedule and what the label says about choosing a maintenance dose.

Zepbound and Mounjaro contain the same active ingredient, tirzepatide, in the same strengths, but they are approved for different conditions.1,4 Mounjaro is approved to improve blood sugar control in adults and children 10 and older with type 2 diabetes, and to reduce the risk of major cardiovascular events in adults with type 2 diabetes at high risk.4 Zepbound is approved for weight reduction and obstructive sleep apnea.1

Both are sold in 2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg and 15 mg strengths, and both have a maximum adult dose of 15 mg once weekly.1,4 The Zepbound label states that using it together with any other tirzepatide-containing product or any GLP-1 receptor agonist is not recommended.1

Because the indications differ, insurers often treat the two drugs differently. See Mounjaro vs Zepbound, plus the price breakdowns for Zepbound and Mounjaro.

No. Compounded tirzepatide is mixed by a pharmacy, and the FDA states that compounded drugs are not FDA-approved and are not reviewed by the agency for safety, effectiveness or quality before they are marketed.9 Our comparison of compounded tirzepatide vs Zepbound and the explainer on compounded tirzepatide cover the differences, and our compounded tirzepatide rankings compare the services that sell it.

No. Zepbound is only available as an injection.1 The label lists four presentations: a single-dose prefilled pen, a single-dose vial, a multi-dose vial, and a single-patient-use KwikPen that holds four weekly doses.1 Lilly's patient site currently supports the single-dose pen, the single-dose vial and the KwikPen.8

There is a separate Lilly pill for weight loss. On April 1, 2026, the FDA approved Foundayo (orforglipron), a once-daily oral GLP-1 receptor agonist for chronic weight management.6 Orforglipron is a different molecule: a small, non-peptide drug, not an oral form of tirzepatide.6

Yes. On December 20, 2024, the FDA approved Zepbound as the first medication for moderate to severe obstructive sleep apnea in adults with obesity.3 It is used with a reduced-calorie diet and increased physical activity.1

The approval rested on two 52-week trials in 469 adults with obesity and without type 2 diabetes, one in people using positive airway pressure (PAP) and one in people who were not.3,1 In the trial without PAP, the apnea-hypopnea index (breathing interruptions per hour of sleep) fell by an average of 25.3 events per hour on Zepbound, against 5.3 on placebo.1 In the PAP trial, it fell by 29.3 events per hour, against 5.5.1

For sleep apnea, the recommended maintenance dose is 10 mg or 15 mg once weekly.1

Zepbound is FDA-approved for weight reduction and sleep apnea, but its label carries a boxed warning for thyroid C-cell tumors and several other serious warnings.1 Whether it is safe for a specific person is a decision for a prescriber who knows that person's history.

The boxed warning concerns thyroid C-cell tumors. Tirzepatide caused these tumors in rats, and it is unknown whether it causes them in humans.1 Zepbound must not be used by anyone with a personal or family history of medullary thyroid carcinoma (MTC) or with Multiple Endocrine Neoplasia syndrome type 2 (MEN 2).1

Other warnings on the label include:1

• severe gastrointestinal reactions, and it is not recommended with severe gastroparesis;
• acute kidney injury from dehydration;
• acute gallbladder disease;
• acute pancreatitis;
• serious allergic reactions;
• low blood sugar, mainly with insulin or sulfonylureas;
• worsening diabetic retinopathy in people with type 2 diabetes;
• risk of inhaling stomach contents under anesthesia or deep sedation.

In January 2026, the FDA asked makers of Zepbound, Wegovy and Saxenda to remove the suicidal thoughts and behavior warning, after a review of 91 placebo-controlled trials found no increased risk.7 The FDA still advises patients to tell their clinician about new or worsening depression or unusual mood changes.7

The most common side effects are gastrointestinal: nausea, diarrhea, vomiting and constipation.1 Rates by dose, how long they tend to last, and what the label says about hair loss and fatigue are in our Zepbound side effects guide. Our safety hub covers the warnings across the drug class.

Is Zepbound insulin? No. Zepbound is tirzepatide, a GIP and GLP-1 receptor agonist. It increases the body's own insulin release when blood sugar is high, but it is not insulin.1

Is Zepbound the same as tirzepatide? Yes. Tirzepatide is the active ingredient and Zepbound is the brand name for its weight and sleep apnea uses. Mounjaro is the brand name for its type 2 diabetes uses.1,4

How long does Zepbound stay in your system? The label gives an elimination half-life of about 5 to 6 days, and steady-state blood levels are reached after 4 weeks of weekly dosing.1

Can you take Zepbound while pregnant? No. The label advises stopping Zepbound when pregnancy is recognized, because weight loss offers no benefit during pregnancy and may cause fetal harm.1 It may also reduce the effect of birth control pills for 4 weeks after starting and after each dose increase.1

Who makes Zepbound? Eli Lilly and Company.1 Lilly also makes Mounjaro and Foundayo.4,6

If Zepbound is on the table, the practical questions are cost and access. Our Zepbound cost guide breaks down list and cash prices, does insurance cover Zepbound covers coverage, and the Zepbound savings card explains Lilly's program. To compare prescribing services, see how to get tirzepatide online, or start from Wegovy vs Zepbound and our best GLP-1 options.

This article is for information only and is not medical advice. Zepbound is a prescription drug with real risks and side effects. Talk to a licensed clinician before starting, changing or stopping any treatment.