The 30-second summary
- A new analysis of the SURMOUNT-1 trial, published on 18 September 2026 in Obesity Pillars, followed 690 people on tirzepatide (Mounjaro, Zepbound) for 176 weeks.
- The median regain from each person's lowest weight was 2.7 kg. 70% regained less than 5% of their starting weight, and 8% regained 10% or more.
- The lowest weight came late: on average 21 to 23 months in, and after week 72 for more than half.
- Over 90% had normal blood sugar at the end, however much they regained.
What did the study look at?
Everyone on a weight-loss medicine reaches a lowest point, which researchers call the nadir. After that, the scale usually drifts up a little. For many people, that drift feels like failure. This analysis set out to measure how big the drift usually is, while people keep taking the drug, and whether it matters for health.
The data come from the three-year portion of SURMOUNT-1, the trial that first tested tirzepatide for weight. Everyone in that portion had prediabetes when they started. The analysis kept 690 people who took at least 75% of their doses and lost at least 5% of their weight by their lowest point. That is 90.6% of the 762 tirzepatide-treated participants with prediabetes.
On average they were 48.5 years old, 64.6% were women, and they started at 107.0 kg.
How much weight came back?
At their lowest point, people on 5 mg, 10 mg and 15 mg had lost an average of 19.0%, 24.3% and 26.0% of their starting weight. By week 176 they were at 15.5%, 20.1% and 22.5% below where they started. Average regain from the lowest weight was 3.8 kg, 4.4 kg and 3.7 kg by dose.
The researchers grouped people by how much they regained, measured as a share of starting weight:
| Regain after the lowest weight | Share of people | Median regain | Share of the loss kept |
|---|---|---|---|
| Under 5% | 70% | 1.2 kg | 94.8% |
| 5% to under 10% | 22% | 7.2 kg | 69.9% |
| 10% or more | 8% | 13.7 kg | 44.3% |
Across everyone, the median regain was 2.7 kg, and the median person kept 88.5% of the weight they had lost at their lowest point.
The split was similar at every dose. A higher dose did not protect people from regaining a few kilos.
When did the lowest weight arrive?
Later than most people would guess. The average time to the lowest weight was 21.1 months on 5 mg and 10 mg, and 22.6 months on 15 mg. More than half of participants reached it after week 72.
That matters because 72 weeks is where the original SURMOUNT-1 results were reported, with an average loss of 20.9% on 15 mg (Jastreboff et al., 2022). For many people, the scale was still moving well after the headline number was published. If you are a year in and slowing down, the plateau is not necessarily the end.
Did the regain undo the health gains?
For most people, no. At week 176, 96.1%, 92.6% and 91.2% of the three groups had normal blood sugar, despite all having had prediabetes at the start. Cholesterol and other blood fat improvements held across all three groups.
The 8% who regained 10% or more did lose some ground. By the end, 68% of them were back in the highest waist-to-height risk group, against 45% of those who regained least. Their blood pressure gains also faded. Even so, averaged across doses, the authors report every measure was still better than before treatment.
Compare that with stopping. In SURMOUNT-4, people who switched from tirzepatide to placebo after 36 weeks regained 14.0% of their weight over the next year, while those who stayed on it lost a further 5.5% (Aronne et al., 2024). The new analysis notes that after stopping, even small regains came with a clear rise in blood pressure. Regain on treatment and regain off treatment are not the same thing.
What are the limits?
- It is post hoc. The question was asked after the trial, not built into it.
- Only people with prediabetes, who took most of their doses and lost at least 5%, were included. Results may differ for others.
- The 10% regain group is small, 57 people.
- It is industry-led. Five of the eight authors work for Eli Lilly, which makes tirzepatide.
- It does not say why some people regained more. The authors write that they hope future work will dispel the idea that individual behaviour is the main cause. The study itself did not measure diet or activity.
What does it mean for you?
A few kilos back from your lowest weight, while still on Mounjaro or Zepbound, is the common pattern, not a sign the drug has stopped working. In this study it happened to most people and left their blood sugar gains intact.
Two things help you judge it calmly:
- Watch your waist as well as the scale. The study used waist-to-height ratio because it tracks the fat that drives risk. A tape measure once a month tells you more than a daily weigh-in.
- Protect what the weight is made of. Regain is easier to live with if the weight you kept off was fat, not muscle. A regular protein intake and strength work twice a week are the basis of keeping muscle on a GLP-1.
If you regain 10% or more of your starting weight, or your waist is moving back up, that is a reason to talk to your prescriber, not a reason to change your dose on your own. The authors frame it the same way: a conversation about health, not a verdict on effort.
Sources
- Aronne LJ, Vincent RP, Klein KR, et al. Evaluation of clinical relevance of weight nadirs and weight regain during 3 years of treatment with tirzepatide in participants with obesity or overweight and prediabetes. Obes Pillars 2026. PubMed
- Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide Once Weekly for the Treatment of Obesity. N Engl J Med 2022. PubMed
- Aronne LJ, Sattar N, Horn DB, et al. Continued Treatment With Tirzepatide for Maintenance of Weight Reduction in Adults With Obesity: The SURMOUNT-4 Randomized Clinical Trial. JAMA 2024. PubMed