What Is GIP? The Second Incretin in Tirzepatide
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GIP (glucose-dependent insulinotropic polypeptide)

Also called GIP, GIP receptor agonist, dual agonist, gastric inhibitory polypeptide · Reviewed

Definition: GIP (glucose-dependent insulinotropic polypeptide) is a hormone released by K cells in the upper gut after you eat. Like GLP-1, it is an incretin: it boosts insulin release when blood sugar is up. Tirzepatide (Mounjaro, Zepbound) activates both the GIP and GLP-1 receptors.

How GIP fits with GLP-1

The two incretins together explain why the body releases 2 to 3 times more insulin when sugar is eaten than when the same sugar is given into a vein (Nauck & Meier 2018). GIP comes mostly from the upper gut (K cells), GLP-1 from the lower gut (L cells).

The Mounjaro label says tirzepatide is "a GIP receptor and GLP-1 receptor agonist" built on the GIP amino acid sequence, with an elimination half-life of about 5 days. Retatrutide, still in trials, adds a third target: it activates GIP, GLP-1 and glucagon receptors (Rosenstock 2023).

Worked example: how long the Mounjaro steps take

Counting weeks on the label schedule

  1. The Mounjaro label starts at 2.5 mg once weekly.
  2. It allows increases of 2.5 mg after at least 4 weeks on the current dose, up to 15 mg once weekly in adults.
  3. From 2.5 mg to 15 mg is 5 steps: 5, 7.5, 10, 12.5 and 15 mg.
  4. 5 steps x at least 4 weeks = at least 20 weeks. So the earliest 15 mg dose on this schedule is week 21.

The label raises the dose only if more blood sugar control is needed, so the schedule sets the fastest pace, not a target.

Why it matters when you track doses

Because tirzepatide is weekly with a 5 day half-life, a late shot shifts the whole week. Logging the actual time of each shot, not just the day, shows whether your gap between doses is drifting. Missed dose timing rules differ by product; see missed dose guides.

Read more on Dose Track: Tirzepatide · Mounjaro · Retatrutide

General education drawn from labels and published studies, not personal medical advice. Your prescriber, pharmacist and the label that came with your product are the final word.
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Frequently asked questions

What does GIP stand for?+
Glucose-dependent insulinotropic polypeptide. Older papers call it gastric inhibitory polypeptide.
Does semaglutide act on GIP?+
No. The Wegovy label describes semaglutide as a GLP-1 receptor agonist only. Tirzepatide acts on both GIP and GLP-1 receptors.
What is a dual agonist?+
A drug that activates two receptors. Tirzepatide is a dual GIP and GLP-1 receptor agonist; retatrutide, still in trials, is a triple agonist that adds the glucagon receptor.

Sources

  1. Nauck & Meier. Diabetes Obes Metab 2018 (incretin hormones GIP and GLP-1, review). PMID 29364588
  2. Mounjaro (tirzepatide) US prescribing information, DailyMed
  3. Rosenstock et al. Lancet 2023 (retatrutide, a GIP, GLP-1 and glucagon receptor agonist, phase 2). PMID 37385280
  4. Wegovy (semaglutide) US prescribing information, DailyMed

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