Trial evidence

Tirzepatide weight loss results, week by week

By David Chen·Editor·Reviewed September 2026

The 72-week result is summarized on the SURMOUNT-1 page. This page is the route there: what the trial and its published analyses reported at each checkpoint along the way.

The timeline³

Every participant started at 2.5 mg and stepped up by 2.5 mg every four weeks until they reached the dose they had been assigned. The 5 mg group got there at week 4, the 10 mg group at week 12 and the 15 mg group at week 20. Each checkpoint below names who it was measured in, because the early figures come from analyses of part of the trial rather than all of it.

Month one: the starting dose⁷

The first four weeks are 2.5 mg for everyone, and the Zepbound label is explicit about what that dose is for: “The 2.5 mg dosage is for treatment initiation and is not approved as a maintenance dosage.” The label ties the gradual escalation to reducing the risk of gastrointestinal side effects. Nobody in SURMOUNT-1 stayed on 2.5 mg: it was the first rung for every arm, including the one assigned to 5 mg.

So a first month with modest change is what the schedule is built to produce, not a verdict on the drug. The label’s timing, and what the trial showed about when results appear, is set out in how long tirzepatide takes to work.

Months two and three²

By week 8, every participant had spent four weeks at 2.5 mg and four at 5 mg, whatever dose they were heading for. An analysis of the 1,775 SURMOUNT-1 participants on tirzepatide with a week-8 weight found that 1,103 (62.1%) had already lost 5% or more. Their average change at that point was −7.9%; the rest averaged −3.1%.

At week 12 a second analysis³ looked at the 1,545 participants who had taken at least three-quarters of their doses and had weights recorded at weeks 0, 12, 24 and 72. 1,267 (82.0%) had lost 5% or more by then; 278 (18.0%) had not. Most of that second group got there later: 70% by week 24 and 90% by week 72. What those slower starters went on to lose, and how few never reached 5%, is covered in why some people are not losing weight on tirzepatide.

Month six: most of the loss⁴

An analysis of weight plateaus in SURMOUNT-1 states it directly: percent body weight reduction was greatest in the first 24 weeks of treatment. Across four groups by starting BMI, the average change from baseline to week 24 was −13.3% to −14.5%, and it was similar across them.

What happened next depended on starting weight. Between weeks 24 and 72, the group that started in the overweight range lost a further 4.6% on average, while the three obesity classes lost a further 7.0%, 8.8% and 9.7%.

Read the population before the number. This analysis included only the 1,438 participants who took at least 75% of their doses, reached their assigned dose by week 24, never had it reduced, and had lost at least 5% by week 72. That is a group selected for responding, so its week-24 average is likely to run ahead of what the whole trial would show at the same point.

Week 72: the trial result¹

These are the trial’s co-primary results in all 2,539 people randomized, whether or not they kept taking the drug. Unlike the earlier checkpoints, they are split by dose, and the gap between 5 mg and 10 mg is larger than the gap between 10 mg and 15 mg. The full summary, including the 20%-or-more threshold, is on the SURMOUNT-1 page.

What that averages per week¹

SURMOUNT-1 reports its result at 72 weeks, not as a weekly rate. Dividing one into the other is something people do in their heads, so here it is done openly. The 72-week average divided by 72 comes to about 0.21%, 0.27% and 0.29% of body weight a week at 5, 10 and 15 mg, against 0.04% on placebo. At the trial’s average starting weight of 104.8 kg (about 231 pounds), 0.29% is roughly two-thirds of a pound a week.

That straight line is the wrong shape, though, and the week-24 figures above show why. In the selected group analyzed for plateaus⁴, the first 24 weeks worked out to roughly 0.55% to 0.60% a week, and weeks 24 to 72 to roughly 0.10% to 0.20% a week, depending on starting BMI. Those rates are our arithmetic on the published averages, not figures the papers report.

After 72 weeks⁵

Participants who had prediabetes at the start stayed on their assigned dose for 176 weeks, a little over three years. Their average weight change at week 176 was −12.3%, −18.7% and −19.7% at 5, 10 and 15 mg, against −1.3% on placebo. That is a subgroup, so it is not a continuation of the 72-week figures above; the authors describe the reduction over three years of treatment as substantial and sustained.

What happens when it does not continue was measured separately.⁶ In SURMOUNT-4, adults who had lost an average 20.9% over 36 weeks were randomized to continue or to switch to placebo; over the next 52 weeks those who continued lost a further 5.5% and those switched regained 14.0%. The trial is summarized on SURMOUNT-4.

Zepbound, Mounjaro and a compounded vial⁷

“Zepbound results” and “tirzepatide results” are the same results. The Zepbound label reports SURMOUNT-1 as its Study 1, under the same registration number (NCT04184622), with the same 72-week figures. Mounjaro is tirzepatide under a type 2 diabetes label⁸, and in type 2 diabetes the weight result was smaller: in the Zepbound label’s Study 2, adults with type 2 diabetes changed by −12.8% and −14.7% at 10 and 15 mg over the same 72 weeks, against −3.2% on placebo. How the two brands differ is set out in Mounjaro vs Zepbound.

A 72-week course is also the horizon a monthly price should be multiplied over; the price index states every seller’s figure as a true calendar month for that reason.

This page reports what a trial measured in groups of people. It is not medical advice and it is not a prediction of anyone’s results; whether a dose or a timeline is right for you is a question for your prescriber. See the medical disclaimer.