Tirzepatide weight loss plateaus within about six to nine months, analysis of two trials finds

A post hoc analysis of two tirzepatide trials found that weight loss generally levels off within roughly six to nine months of starting the drug, and that most participants had plateaued by week 72. The analysis, published in the journal Clinical Obesity, looked at when weight loss stopped rather than how much weight people lost ^[1].

Tirzepatide is sold as Mounjaro for type 2 diabetes and Zepbound for chronic weight management ^[1].

What the analysis found

Researchers looked back at two phase 3 trials, SURMOUNT-1 and SURMOUNT-4, which tested tirzepatide in adults with obesity or overweight ^[1]. The analysis included 1,438 participants from SURMOUNT-1 and 259 from SURMOUNT-4 who were adherent to treatment and had lost at least 5% of their body weight by the trial's primary endpoint, which was week 72 in SURMOUNT-1 and week 88 in SURMOUNT-4 ^[1].

The researchers defined a plateau as a weight change of less than 5% over a 12-week period, and over every 12-week period after that. Time to plateau was measured from randomization to the start of the first such 12-week stretch ^[1].

Median time to plateau in SURMOUNT-1 varied by starting BMI category. It was 24.3 weeks for participants who started with overweight, 26.0 weeks for class I obesity, and 36.1 weeks for both class II and class III obesity. The difference between class II and class III versus overweight was statistically significant (p < .05) ^[1].

By week 72, most participants had plateaued: 90.2% of those in the overweight category, 88.9% in class I, 87.6% in class II and 87.8% in class III ^[1]. Results in SURMOUNT-4 were similar, though the published abstract does not give median times for that trial ^[1].

Three factors were associated with a later plateau: higher tirzepatide doses (10 mg or 15 mg), younger age, and female sex ^[1].

What the analysis does not cover

This was a post hoc analysis, meaning the question was asked after the trials were designed and run, not as a pre-planned main goal. It included only people who stayed on tirzepatide and who had already lost at least 5% of their body weight, so the findings do not describe everyone who starts the medication. The analysis did not report whether the timing of a plateau was tied to health outcomes.

Several authors are employees and shareholders of Eli Lilly, which makes tirzepatide, and other authors reported advisory board roles or consulting fees from Lilly and other drugmakers ^[1].

The abstract does not say whether similar plateau patterns apply to semaglutide (Ozempic, Wegovy, Rybelsus) or to other weight-loss drugs.

Why it matters for patients

A plateau is the expected course of treatment in these trials, not evidence that the drug has stopped working or that a person has failed. In these studies, weight loss slowed and then leveled off for the large majority of participants by just over a year, and the timing varied with starting BMI category, dose, age and sex ^[1].

For someone tracking weekly weight, that context may be useful when discussing progress with a clinician. The analysis does not say what should be done when a plateau is reached, and it did not test any change in dose, drug or approach at that point.

Because the analysis was limited to people who lost at least 5% of body weight and stayed on treatment, it cannot say how often plateaus occur among people who lose less weight or who stop tirzepatide early.

What happens next

The authors wrote that further research into what modifies the phases of weight reduction with tirzepatide may inform treatment decisions for its use in long-term weight management ^[1]. No new trials or dated milestones were announced with the publication, and no timeline for follow-up analyses has been reported ^[1].