Mounjaro (tirzepatide) is a once-weekly injection that activates two gut hormone receptors — GIP and GLP-1 — to powerfully reduce appetite and food intake. In head-to-head trial data it has produced some of the largest weight loss results of any approved medication. Use our free calculator to estimate your personal trajectory based on the SURMOUNT-1 study.
The strongest evidence comes from the SURMOUNT-1 trial, a 72-week, double-blind, randomized, placebo-controlled study of 2,539 adults with obesity (without diabetes), published in the New England Journal of Medicine in 2022.
Source: Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide Once Weekly for the Treatment of Obesity. N Engl J Med. 2022;387(3):205-216. PMID: 35658024
For a person weighing 220 lbs (100 kg), a 22.5% reduction works out to roughly 50 lbs (22 kg) over about 17 months on the maximum dose. Real-world results vary with starting weight, adherence, diet, activity, and the dose you tolerate.
Mounjaro is increased gradually to reduce nausea and other GI side effects. The standard titration is:
| Weeks | Weekly Dose | Phase |
|---|---|---|
| 1–4 | 2.5 mg | Starting dose (not for weight loss yet — tolerance) |
| 5–8 | 5 mg | First therapeutic dose |
| 9–12 | 7.5 mg | Maintenance or step-up |
| 13–16 | 10 mg | Maintenance or step-up |
| 17–20 | 12.5 mg | Step-up |
| 21+ | 15 mg | Maximum dose |
Need to convert a prescribed dose into pen units? Use our GLP-1 dose calculator.
Mounjaro is FDA-approved for type 2 diabetes, not specifically for weight loss. The identical medication (tirzepatide) is FDA-approved for chronic weight management under the brand name Zepbound. Mounjaro is widely prescribed off-label for obesity because it contains the same active ingredient at the same doses.
In clinical trials, tirzepatide (Mounjaro) produced greater average weight loss than semaglutide (Ozempic). SURMOUNT-1 showed up to 22.5% body weight loss on tirzepatide 15 mg over 72 weeks, compared with about 14.9% on semaglutide 2.4 mg in STEP-1. Tirzepatide's dual GIP/GLP-1 mechanism is thought to drive the difference.
Mounjaro is titrated slowly to limit side effects. You start at 2.5 mg weekly for 4 weeks, then increase by 2.5 mg every 4 weeks (5, 7.5, 10, 12.5) up to a maximum of 15 mg. Reaching the top dose therefore takes a minimum of about 20 weeks, and many people stay at a lower dose if it controls appetite well.
The SURMOUNT-4 trial showed that people who stopped tirzepatide regained much of the weight they had lost, while those who continued kept losing. GLP-1/GIP medications are designed for long-term use alongside sustainable diet and lifestyle changes, not as a short course.
Our free calculator uses SURMOUNT-1 trial data to project your personalized week-by-week weight loss timeline.
Try Our Full GLP-1 Weight Loss CalculatorThis calculator is for informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Weight loss projections are estimates based on average clinical trial results and may not reflect your individual experience. Mounjaro (tirzepatide) is a prescription medication that should only be used under the supervision of a qualified healthcare provider. Always consult your doctor before starting, stopping, or changing any medication.