Definition
GIP (glucose-dependent insulinotropic polypeptide) is a second gut hormone. A dual agonist, such as tirzepatide, activates both GIP and GLP-1 receptors. Tirzepatide is sold as Mounjaro for type 2 diabetes and as Zepbound for weight reduction and sleep apnea.
GIP and GLP-1 are the two known incretin hormones. GIP comes from the upper gut and GLP-1 from the lower gut, and both help the pancreas release insulin after a meal when blood sugar is high. Tirzepatide is one molecule built to activate both receptors. The Zepbound label notes that GIP and GLP-1 receptors are both found in brain areas that regulate appetite, and that nonclinical studies suggest GIP may add to the control of food intake.
In the Zepbound label, adults without diabetes lost an average of 15.0%, 19.5% and 20.9% of body weight over 72 weeks on 5, 10 and 15 mg, compared with 3.1% on placebo. The side effects look like the rest of the class: nausea in 25% to 29% of people vs 8% on placebo, with most nausea, vomiting and diarrhea during dose increases. One difference worth knowing: tirzepatide labels advise adding a barrier method or switching from the pill for 4 weeks after starting and after each dose increase if you use oral birth control.
The labels say not to use tirzepatide together with any GLP-1 receptor agonist. At GLP-1 SOS we hear from many people who moved from semaglutide to tirzepatide or back. The gut side effects are similar, so the same answers in the Lab apply to both.
In the Lab
- GLP-1 dose increase side effects: what is normal in the first week
- Why did my GLP-1 stop working?
- Is a plateau normal on a GLP-1 (and when)?
- Why a GLP-1 causes diarrhea (and why it alternates with constipation)
From the people behind the Lab
You do not have to figure this out alone.
GLP-1 SOS is the daily companion made for life on a GLP-1. Plain answers like this one, a support team that replies to real questions from real people, and daily formulas like GLP-1 SOS Daily Gut Relief, designed around the side effects that come with the medication. The GLP-1 Lab is our free education arm: no login, no paywall, no hype. Side effects are part of the road. Suffering through them is not.
Sources (4)
- Zepbound (tirzepatide) injection, Prescribing Information. Eli Lilly, revised August 2026.
- Mounjaro (tirzepatide) injection, Prescribing Information. Eli Lilly, revised August 2026.
- Incretin hormones: Their role in health and disease. Diabetes, Obesity and Metabolism, 2018.
- Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). New England Journal of Medicine, 2022.
Reviewed by the GLP-1 SOS editorial team · Education, not medical advice · Talk to your prescriber about your dose and your symptoms.
