At a glance

What is tirzepatide?

Tirzepatide is a synthetic peptide made of 39 amino acids that acts as a dual GIP and GLP-1 receptor agonist¹. GIP and GLP-1 are two hormones the gut releases after eating, and tirzepatide is engineered to activate both of their receptors at once, which is what distinguishes it from the single-hormone GLP-1 drugs.

It is made by Eli Lilly and sold under two brand names. Mounjaro is used for type 2 diabetes, and Zepbound is used for weight management and for obstructive sleep apnea. Both are given as a once-weekly subcutaneous injection¹.

How does it work?

Tirzepatide activates the GIP and GLP-1 receptors, mimicking two natural gut hormones at the same time. Through those receptors it prompts the pancreas to release insulin¹ when blood sugar is high, reduces the release of glucagon (a hormone that raises blood sugar), slows the rate at which the stomach empties, and acts on appetite centers to reduce hunger and food intake. Together these effects lower blood sugar and reduce how much a person eats.

The trial results are large. In the SURMOUNT-1 obesity trial, adults without diabetes lost an average of between 15.0% and 20.9%² of their body weight across the three doses over 72 weeks, compared with 3.1% for placebo. In its type 2 diabetes program, tirzepatide produced large reductions¹ in blood sugar (A1c) along with weight loss.

Is tirzepatide FDA-approved?

Yes, across five uses, approved in this order:

What is tirzepatide prescribed for?

For type 2 diabetes, Mounjaro is prescribed to improve blood sugar control alongside diet and exercise in adults and children 10 and older, and to reduce the risk of major cardiovascular events in adults with type 2 diabetes at high risk. For weight management, Zepbound is approved for adults with obesity (a BMI of 30 or higher) or overweight (a BMI of 27 or higher) plus a weight-related condition such as high blood pressure or high cholesterol. Zepbound is also approved for moderate-to-severe obstructive sleep apnea³ in adults with obesity.

It should not be used by people with a personal or family history of medullary thyroid carcinoma¹ or Multiple Endocrine Neoplasia syndrome type 2, or by anyone with a known allergy to tirzepatide.

What are the side effects?

The most common side effects are gastrointestinal, and they are usually strongest when the dose is increased:

• Nausea
• Diarrhea
• Vomiting
• Constipation
• Abdominal pain
• Decreased appetite
• Indigestion
• Fatigue
• Injection-site reactions
• Allergic reactions
• Belching
• Hair loss
• Heartburn

Less common but more serious risks include:

• Thyroid C-cell tumors: tirzepatide carries a boxed warning¹ based on rodent studies. It is not known whether this happens in humans.
• Pancreatitis, or inflammation of the pancreas
• Gallbladder problems, including gallstones
• Acute kidney injury, usually from dehydration caused by vomiting or diarrhea
• Worsening of diabetic retinopathy in people with type 2 diabetes
• Low blood sugar, especially when combined with insulin or a sulfonylurea
• Delayed stomach emptying, which can raise the risk of aspiration during surgery or anesthesia

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