Definition
Tirzepatide is a once-weekly injection that activates both GIP and GLP-1 receptors. It is the active ingredient in Mounjaro and Zepbound. Mounjaro is approved for type 2 diabetes. Zepbound is approved for weight reduction and for moderate to severe sleep apnea in adults with obesity.
Tirzepatide is a dual GIP/GLP-1 agonist. It carries a fatty acid chain that binds to albumin in the blood, which stretches its half-life to about 5 days. The Zepbound label says steady levels are reached after 4 weeks of weekly shots. Like other GLP-1 medicines, it slows the stomach; the label notes this effect is largest after the first dose and fades over time.
Both labels start at 2.5 mg once a week for 4 weeks, then go up in 2.5 mg steps after at least 4 weeks on each dose. For Zepbound, the maintenance dose is 5, 10 or 15 mg (10 or 15 mg for sleep apnea), and 15 mg is the maximum. In the Zepbound label, adults lost an average of 15.0% to 20.9% of body weight over 72 weeks, depending on the dose, vs 3.1% on placebo. Nausea affected 25% to 29% vs 8%, and constipation 11% to 17% vs 5%.
If you use birth control pills, the labels advise switching to a non-oral method or adding a barrier method for 4 weeks after starting and after each dose increase. At GLP-1 SOS we hear the most tirzepatide questions in the week after a dose step.
In the Lab
- GLP-1 dose increase side effects: what is normal in the first week
- What to do when nothing works for constipation on a GLP-1
- Still hungry on a GLP-1: is it normal and what does it mean?
- How long before a GLP-1 starts working (appetite and weight)
From the people behind the Lab
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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 (3)
Reviewed by the GLP-1 SOS editorial team · Education, not medical advice · Talk to your prescriber about your dose and your symptoms.
