Tirzepatide is a once-weekly injection that activates two gut-hormone receptors, GIP and GLP-1, and it can lead to substantial weight loss. It is sold as Zepbound, which the FDA approved for weight management and for moderate to severe obstructive sleep apnea in adults with obesity, and as Mounjaro, which is approved for type 2 diabetes. In the Zepbound label’s 72-week trial, adults on the 15 mg dose lost 20.9% of body weight on average versus 3.1% on placebo (Zepbound prescribing information, section 14).
Zepbound vs Mounjaro
| Zepbound | Mounjaro | |
|---|---|---|
| Active ingredient | tirzepatide | tirzepatide |
| Approved use | Weight reduction and maintenance in adults with obesity, or overweight plus a weight-related condition; moderate to severe obstructive sleep apnea in adults with obesity | Type 2 diabetes (adults and children 10+): blood sugar control; lower cardiovascular risk in adults with type 2 diabetes at high risk |
| Schedule | Weekly injection | Weekly injection |
| Maker | Eli Lilly | Eli Lilly |
Sources: Zepbound and Mounjaro prescribing information, section 1 of each. For a closer look see the Mounjaro guide and the Zepbound guide.
How tirzepatide works
Tirzepatide is a GIP receptor and GLP-1 receptor agonist. GLP-1 is a physiological regulator of appetite and calorie intake; the label notes that nonclinical studies suggest adding GIP may further contribute to regulating food intake, and that both receptors are found in brain areas involved in appetite (Zepbound label, section 12.1). This dual action is what separates it from semaglutide, which acts on GLP-1 only. See Zepbound vs Wegovy for how the two compare.
Dosing
The label starts low and raises the dose in steps to reduce stomach side effects. Your prescriber decides the plan.
| Step | Weekly dose | Duration |
|---|---|---|
| Start | 2.5 mg | 4 weeks (initiation only, not a maintenance dose) |
| Next | 5 mg | At least 4 weeks |
| Then, if needed | Increase in 2.5 mg steps | At least 4 weeks on each dose |
| Maximum | 15 mg |
For weight reduction the label’s maintenance doses are 5 mg, 10 mg or 15 mg weekly; for sleep apnea, 10 mg or 15 mg. Mounjaro follows the same 2.5 mg start and 2.5 mg steps, with a maximum of 15 mg for adults. Sources: Zepbound section 2.1 and 2.2, Mounjaro section 2.1.
The injection is given under the skin of the abdomen or thigh, or into the back of the upper arm by another person, once weekly, at any time of day, with or without food. If a Zepbound dose is missed, take it as soon as possible within 4 days (96 hours); after that, skip it and take the next one on the usual day. The injection day can be changed as long as doses are at least 3 days (72 hours) apart. For a week-by-week view, see the Zepbound dosage schedule.
What the trials showed
The Zepbound label reports two 72-week trials where people also followed a reduced-calorie diet and increased activity (Table 2):
- Study 1, adults with obesity or overweight and no diabetes: average weight change of -15.0% (5 mg), -19.5% (10 mg) and -20.9% (15 mg), versus -3.1% on placebo. The share who lost at least 5% of body weight was 85.1%, 88.9% and 90.9% for the three doses.
- Study 2, adults with type 2 diabetes: -12.8% (10 mg) and -14.7% (15 mg), versus -3.2% on placebo.
The first trial is published as SURMOUNT-1 (NEJM, 2022). These are trial averages; individual results vary, and the label ties benefit to ongoing treatment alongside lifestyle changes.
Side effects
In the label’s pooled weight-loss trials (Table 1), compared with placebo: nausea 25% to 29% vs 8%, diarrhea 19% to 23% vs 8%, vomiting 8% to 13% vs 2%, and constipation 11% to 17% vs 5%, depending on dose. The label also carries a boxed warning on thyroid C-cell tumors seen in rats, and warns about severe gastrointestinal reactions, acute kidney injury from dehydration, gallbladder disease, pancreatitis, allergic reactions, low blood sugar when combined with insulin or sulfonylureas and diabetic retinopathy complications. It is contraindicated with a personal or family history of medullary thyroid carcinoma or MEN 2.
Talk to your prescriber if symptoms are severe or do not settle, and before changing a dose. See GLP-1 side effects: what to expect and how to manage them.
Who should talk to a prescriber first
Tirzepatide is a prescription medicine. Tell your prescriber about a personal or family history of thyroid cancer, pancreatitis, gallbladder disease, kidney problems, diabetic eye disease and all other medicines you take (the label notes tirzepatide delays stomach emptying and can affect absorption of oral medicines). Planned surgeries or procedures under sedation should also be mentioned, as the label warns about pulmonary aspiration with GLP-1 receptor agonists. Obtain it from a licensed pharmacy: the FDA says unapproved versions are not reviewed for safety, effectiveness and quality.
Habits and tracking
The label approves tirzepatide for use with a reduced-calorie diet and more physical activity, so food, protein, hydration and movement still matter. A log helps you see how your weight, appetite and symptoms change with each dose step:
- Injection day, dose and site
- Side effects and timing
- Meals, protein and water
- Weekly weight
Mingo is a GLP-1 tracker for iPhone and Android where you can log shots, food and protein, side effects and weight in one place. It doesn’t replace your doctor. Get the app.
Key takeaways
- Tirzepatide acts on GIP and GLP-1 receptors. Zepbound is approved for weight management and sleep apnea; Mounjaro for type 2 diabetes.
- Doses start at 2.5 mg and rise in 2.5 mg steps at least 4 weeks apart, up to 15 mg.
- In the Zepbound label’s trial, 15 mg averaged -20.9% body weight vs -3.1% on placebo over 72 weeks.
- Nausea, diarrhea, vomiting and constipation are the most common side effects; report severe or lasting symptoms.
Frequently asked questions
What is tirzepatide used for?
As Zepbound, it is approved for weight reduction and maintenance in adults with obesity (or overweight plus a related condition) and for moderate to severe obstructive sleep apnea in adults with obesity. As Mounjaro, it is approved for type 2 diabetes.
How does tirzepatide help with weight loss?
It activates both GIP and GLP-1 receptors, which are involved in appetite regulation, so many people feel less hungry. In trials it was combined with a reduced-calorie diet and more physical activity.
What are common side effects of tirzepatide?
Nausea, diarrhea, vomiting and constipation are the most common, usually while the dose is being raised. Serious risks include pancreatitis and gallbladder disease.
How much does tirzepatide cost?
Prices and coverage vary by plan, country and pharmacy and change often, so we do not give a figure. Ask your pharmacist and insurer.
Is tirzepatide safe for everyone?
No. It is contraindicated with a personal or family history of medullary thyroid carcinoma or MEN 2, or a serious allergy to tirzepatide. Your prescriber should review your history before starting.
