- Example
- Tirzepatide (Mounjaro, Zepbound)
- Receptors
- GIP and GLP-1
- Dosing
- Once-weekly injection (branded)
- Boxed warning
- Thyroid C-cell tumors in rodents
Two hormones, one molecule
GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) are incretins, hormones your intestine releases after a meal. Both help the pancreas release insulin when blood sugar is rising. GLP-1 also slows stomach emptying and acts on appetite centers in the brain.
Tirzepatide was engineered to activate both receptors. Researchers are still working out exactly how much the GIP action adds, but the dual approach is thought to be one reason tirzepatide produces large average weight loss.
Approved uses
Tirzepatide is sold under two brand names:
- Mounjaro: approved to improve blood sugar control in adults with type 2 diabetes.
- Zepbound: approved in November 2023 for chronic weight management in adults with a BMI of 30 or more, or 27 or more with at least one weight-related condition, alongside diet and activity. It is also approved to treat obstructive sleep apnea in adults with obesity.
What trials showed
In the FDA's summary of the 72-week trial in adults without diabetes, people on the highest dose (15 mg weekly) lost about 18% more body weight on average than those on placebo. In a trial of adults with type 2 diabetes, the difference was about 12%. These are averages from branded products; individual results vary widely, and weight usually returns if the medicine is stopped without other changes.
Side effects and warnings
Common side effects are digestive: nausea, diarrhea, vomiting, constipation, stomach pain and reduced appetite, mostly when the dose is increased. Important warnings include:
- A boxed warning for thyroid C-cell tumors seen in rodents. It shouldn't be used if you or a family member has had medullary thyroid cancer or if you have multiple endocrine neoplasia type 2 (MEN 2).
- Pancreatitis, gallbladder problems, kidney injury from dehydration and low blood sugar when combined with insulin or sulfonylureas.
- Possible reduced effectiveness of hormonal birth control.
- Not for use in pregnancy.
Compounded tirzepatide
Compounded tirzepatide is not FDA-approved and is not the same as Zepbound or Mounjaro. The FDA has received hundreds of adverse event reports involving compounded tirzepatide, including problems linked to dosing errors and doses above the approved label. At HealifyMD, tirzepatide injection is compounded and starts at $399 per month, confirmed at your eligibility review, and your clinician sets and adjusts the dose.
Whatever product you use, the medicine works best alongside steady changes in eating, activity, sleep and strength training, which help protect muscle as weight comes off.
GIP/GLP-1 dual agonist: common questions
Is tirzepatide a GLP-1?
It's a GLP-1 receptor agonist and a GIP receptor agonist in one molecule, so it's often grouped with GLP-1 medicines but works on two receptors.
How is tirzepatide taken?
The branded products are once-weekly injections under the skin, with the dose increased gradually.
Does tirzepatide cause more weight loss than semaglutide?
Trials of the branded drugs have found larger average weight loss with tirzepatide, though individual responses vary widely and tolerability matters too.
Can tirzepatide affect birth control pills?
Yes. It may make hormonal birth control less effective, so ask your clinician whether you need a backup method.
Is compounded tirzepatide the same as Zepbound?
No. Compounded tirzepatide isn't FDA-approved, and the trials behind Zepbound don't directly apply to it.
Who shouldn't take tirzepatide?
People with a personal or family history of medullary thyroid cancer or MEN 2, those who are pregnant, and anyone with a past serious reaction to it.
Sources
We cite government agencies, professional societies and peer-reviewed research. See our editorial policy.
- FDA Approves New Medication for Chronic Weight Management (Zepbound)U.S. Food and Drug Administration
- Tirzepatide InjectionMedlinePlus (U.S. National Library of Medicine)
- Glucagon-Like Peptide-1 Receptor AgonistsNCBI Bookshelf (StatPearls)
- FDA's Concerns with Unapproved GLP-1 Drugs Used for Weight LossU.S. Food and Drug Administration