Definition: A weight plateau is when weight loss slows and levels off, even though treatment continues. An analysis of the SURMOUNT tirzepatide trials notes that the rate of weight loss during obesity treatment declines over time and eventually reaches a plateau. Most trial participants reached one while still on treatment.
What the trials found
Horn and colleagues (2025), several of them Lilly employees, looked back at SURMOUNT-1 and SURMOUNT-4. They counted a plateau as a weight change under 5% over a 12-week stretch and every 12-week stretch after it. They included only people who stayed on tirzepatide and lost at least 5%.
SURMOUNT-1, median time to weight plateau by starting BMI group.
| Starting BMI group | Median weeks to plateau | Reached plateau by week 72 |
|---|
| Overweight | 24.3 | 90.2% |
| Obesity class I | 26.0 | 88.9% |
| Obesity class II | 36.1 | 87.6% |
| Obesity class III | 36.1 | 87.8% |
Higher doses (10 or 15 mg), younger age and female sex were linked with reaching a plateau later. SURMOUNT-4 results were similar.
Putting the numbers in context
Reading the medians
- 24.3 weeks ÷ 4.3 weeks per month = about 5.7 months. 36.1 weeks is about 8.4 months.
- In STEP 1, semaglutide 2.4 mg weekly gave a mean weight change of −14.9% at week 68, against −2.4% on placebo.
- A median is the middle person. Half reached a plateau sooner, half later.
These are group results from trials. They do not say when any one person will plateau or what to do about it.
Common mix-ups
- A plateau is not the same as the drug wearing off. The papers above describe a slowing of weight loss, not a measured loss of drug effect. For that idea, see tachyphylaxis.
- Drug levels leveling off is a different idea. That is steady state.
Read more on Dose Track: Tirzepatide guide · Semaglutide guide
General education drawn from labels and published studies, not personal medical advice. Your prescriber, pharmacist and the label that came with your product are the final word.
When do people usually hit a weight plateau on tirzepatide?+
In a SURMOUNT-1 analysis the median time was 24 to 36 weeks, depending on starting BMI, and about 88% to 90% had reached a plateau by week 72.
Does a plateau mean the medicine stopped working?+
Not by itself. In the trial analysis, most people who stayed on tirzepatide reached a plateau, as weight loss slowed and leveled off. Talk to your prescriber about your own results.