The tirzepatide dosage that built the weight-management label is 5, 10 or 15 mg once weekly, every arm starting at 2.5 mg and stepping up 2.5 mg every four weeks. It looks settled until you notice the same trial gets quoted with two different headline results. Both numbers are real, and we'll show you where each comes from.
The short version
SURMOUNT-1 used 5, 10 and 15 mg once weekly over 72 weeks, with every arm starting at 2.5 mg and stepping up 2.5 mg every four weeks to its target. Weight change on the intent-to-treat analysis was −15.0%, −19.5% and −20.9% against −3.1% for placebo. Reaching 15 mg takes about 20 weeks of escalation.
Tirzepatide is one of the few compounds in our library where the dosing question has a real answer. It's an approved drug with a label: Mounjaro for type 2 diabetes, Zepbound for weight management.
What follows is the protocol from SURMOUNT-1, the trial that built the weight-management indication.
The SURMOUNT-1 protocol
Jastreboff and colleagues randomized 2,539 adults with obesity across 119 sites in nine countries, 1:1:1:1 to tirzepatide 5 mg, 10 mg, 15 mg or placebo, dosed subcutaneously once weekly for 72 weeks alongside lifestyle intervention. It remains the largest and most rigorous obesity trial the incretin class has produced.
| Week | Dose | Note |
|---|---|---|
| 1–4 | 2.5 mg weekly | Tolerability step, not a therapeutic dose |
| 5–8 | 5 mg weekly | Target reached for the 5 mg arm |
| 9–12 | 7.5 mg weekly | Intermediate step |
| 13–16 | 10 mg weekly | Target reached for the 10 mg arm |
| 17–20 | 12.5 mg weekly | Intermediate step |
| 21+ | 15 mg weekly | Target reached for the 15 mg arm |
The four-week interval is the class standard, and it exists because roughly four weeks is how long gastrointestinal tolerance takes to develop at a given dose. Retatrutide's Phase 2 used the same rhythm; so did semaglutide's STEP-1.
What each dose produced
| Arm | Weight change at 72 weeks (ITT) | Versus placebo |
|---|---|---|
| Placebo | −3.1% | — |
| 5 mg | −15.0% | −11.9 pts |
| 10 mg | −19.5% | −16.4 pts |
| 15 mg | −20.9% | −17.8 pts |
Why you see both 20.9% and 22.5%. It isn't an error, and they aren't two different trials. They're two different estimands.
The 20.9% figure is intent-to-treat, so it counts everyone randomized, including those who stopped. The 22.5% figure describes the effect among participants who stayed on treatment.
Intent-to-treat is the conservative number and the one that compares across trials, which is why we lead with it. Anyone quoting 22.5% against another drug's ITT figure is stacking the comparison.
91% of participants reached at least 5% weight reduction and 57% reached at least 20%. The full SURMOUNT-1 breakdown covers the design and the maintenance follow-up.
The tolerability cost
SURMOUNT-1 reported nausea in 33%, diarrhea in 22% and vomiting in 12% of participants. Most cases were mild to moderate, and concentrated during dose escalation rather than spread across the 72 weeks.
That's the pattern that makes slow titration worthwhile. The gut adapts, and it adapts faster than the dose climbs.
The follow-up SURMOUNT-4 trial added the finding that reframed the whole drug. Discontinuation produced major weight regain, which makes tirzepatide chronic therapy rather than a course of treatment.
GLP2-T (tirzepatide)
The dual-agonist reference compound behind the SURMOUNT trial literature. Research use only — supplied with a batch-matched certificate of analysis.
Research tirzepatide is not Zepbound
The sequence can be identical. Everything around it isn't. An approved product carries GMP manufacturing, sterile fill-finish, endotoxin and sterility assurance, batch release testing, stability programs and a regulator who can force a recall.
Research material carries synthesis, plus third-party analytical testing on the powder if you selected for it.
That distinction matters more here than for most compounds, because tirzepatide has an approved alternative. If you're weighing the two, you're choosing between a regulated drug product and an unregulated reference compound, not between two prices for the same thing.
- Start at 2.5 mg in the protocol, not at target. Every SURMOUNT-1 arm did, and the opening dose is a tolerability step rather than a therapeutic one.
- Budget about 20 weeks to reach 15 mg. That's a large share of a 72-week trial spent below target dose.
- Compare ITT to ITT. The 20.9% and 22.5% figures answer different questions, and mixing them flatters whichever drug gets the second one.
What research grade guarantees and the 503A compounding route cover the middle ground. Our where to buy tirzepatide page has the sourcing checks specific to this compound.
What we’re watching
The maintenance question is the live one. SURMOUNT-4 showed regain on withdrawal, and we're watching whether any dose below 15 mg holds weight as well over multi-year follow-up.
We're also watching the oral incretins. If a small-molecule agonist reaches a similar ITT figure, the escalation arithmetic on this page stops being the only way to get there.
Frequently asked questions
What doses of tirzepatide were used in SURMOUNT-1?
5 mg, 10 mg and 15 mg once weekly, subcutaneously, over 72 weeks. Every arm started at 2.5 mg weekly for four weeks, then stepped up by 2.5 mg every four weeks until it reached its assigned target.
What is the starting dose of tirzepatide?
2.5 mg once weekly for the first four weeks in SURMOUNT-1. That opening dose is explicitly a tolerability step rather than a therapeutic one. It exists to let the gut adapt before the dose starts climbing.
How long does tirzepatide dose escalation take?
Reaching 15 mg from 2.5 mg in 2.5 mg increments every four weeks takes roughly 20 weeks. That is a substantial fraction of a 72-week trial spent below target dose, which is worth remembering when reading the headline result.
How much weight did each tirzepatide dose produce?
On the intent-to-treat analysis at 72 weeks: −15.0% at 5 mg, −19.5% at 10 mg and −20.9% at 15 mg, against −3.1% on placebo. The often-quoted 22.5% figure comes from a different estimand that measures the effect among those who stayed on treatment.
Is research tirzepatide the same as Mounjaro or Zepbound?
The molecule can be the same. The product is not. Mounjaro and Zepbound are GMP-manufactured, sterile-filled, batch-released drug products with a regulator behind them. Research tirzepatide is lyophilized powder with, at best, analytical testing on the powder.
GLP2-T (tirzepatide)
Research-use-only material, sold by the vial with batch documentation. Check the certificate of analysis against the batch you receive.
What to know now
- SURMOUNT-1 used 5, 10 and 15 mg once weekly. The trial ran 72 weeks, with every arm starting at 2.5 mg.
- Escalation is slow by design. Doses rose 2.5 mg every four weeks, so reaching 15 mg takes about 20 weeks.
- Intent-to-treat change was −15.0%, −19.5% and −20.9%. Placebo came in at −3.1% over the same period.
- The dose carries a tolerability cost. The step-up schedule exists because the higher doses are harder to tolerate, not because they act slowly.
- Research tirzepatide is not Zepbound. Trial doses were given as an approved product under supervision, which a research vial does not replicate.
References
- Jastreboff, A. M., Aronne, L. J., Ahmad, N. N., et al. (2022). Tirzepatide once weekly for the treatment of obesity. New England Journal of Medicine, 387(3), 205–216. https://doi.org/10.1056/NEJMoa2206038
- Aronne, L. J., Sattar, N., Horn, D. B., et al. (2024). Continued treatment with tirzepatide for maintenance of weight reduction in adults with obesity: The SURMOUNT-4 randomized clinical trial. JAMA, 331(1), 38–48. https://doi.org/10.1001/jama.2023.24945
- Wilding, J. P. H., Batterham, R. L., Calanna, S., et al. (2021). Once-weekly semaglutide in adults with overweight or obesity (STEP-1). New England Journal of Medicine, 384(11), 989–1002. https://doi.org/10.1056/NEJMoa2032183
- Jastreboff, A. M., Kaplan, L. M., Frías, J. P., Wu, Q., Du, Y., Gurbuz, S., Coskun, T., Haupt, A., Milicevic, Z., & Hartman, M. L. (2023). Triple–hormone-receptor agonist retatrutide for obesity — A phase 2 trial. New England Journal of Medicine, 389(6), 514–526. https://doi.org/10.1056/NEJMoa2301972
The 20.9% and 22.5% figures are the intent-to-treat and treatment-regimen estimands from the same SURMOUNT-1 publication.