The SURMOUNT-1 results are straightforward: after 72 weeks, average weight change was -15.0%, -19.5%, and -20.9% in the three tirzepatide groups, compared with -3.1% in the placebo group. The study followed 2,539 adults with obesity or overweight who did not have diabetes. Those are group averages, not a forecast for one person.
What question did the SURMOUNT-1 trial ask?
SURMOUNT-1 asked whether once-weekly tirzepatide, alongside nutrition and activity support, would produce a larger average change in body weight than the same support plus placebo. A placebo is a look-alike injection without tirzepatide.
It was a phase 3 trial, a large late-stage study designed to confirm results and track harm. It was randomized, so assignment happened by chance, and double-blind, so participants and investigators did not know the assignments. The paper appeared in the New England Journal of Medicine in 2022, and the completed ClinicalTrials.gov record is NCT04184622. Eli Lilly funded the study.
Who took part and for how long?
The trial enrolled 2,539 adults. Their mean age was 44.9 years, about two-thirds were women, and their average starting weight was 104.8 kg, or about 231 pounds. Average BMI was 38.0; BMI is a height-to-weight screening number, not a full picture of health.
Participants qualified with a BMI of at least 30, or at least 27 plus a condition such as high blood pressure, abnormal cholesterol, sleep apnea, or cardiovascular disease. Diabetes was excluded. So were a weight change greater than 5 kg in the prior three months, recent weight-management medication, and previous or planned obesity surgery.
The treatment period lasted 72 weeks and included 20 weeks of planned dose escalation. That controlled schedule matters: the trial did not test every pace or every individualized dosing plan used in ordinary care.
How did the study measure the endpoints?
The two primary endpoints, meaning the main results chosen before the study began, were percentage change in body weight and the share of participants who lost at least 5% by week 72.
The headline analysis kept people in their originally assigned groups even if they stopped treatment. That approach gives a more practical estimate than counting only people who completed every dose. Lifestyle support was part of every group, including placebo.
SURMOUNT-1 results by dose
The dose groups were fixed assignments, not instructions for a reader. The prescriber sets an individual's dose.
| Assigned weekly dose | Average weight change at week 72 | Lost at least 5% |
|---|---|---|
| Tirzepatide 5 mg | -15.0% | 85.1% |
| Tirzepatide 10 mg | -19.5% | 88.9% |
| Tirzepatide 15 mg | -20.9% | 90.9% |
| Placebo | -3.1% | 34.5% |
Put plainly, about 9 in 10 people in the 15 mg group crossed the 5% mark, compared with about 1 in 3 on placebo. That does not mean everyone on 15 mg lost 20.9%. The first figure is a share of people crossing a threshold; the second is the group's average. The broader tirzepatide weight-loss results page follows the curve over time.
Side effects reported in the paper
Stomach and bowel problems were the most common side effects. Most were mild or moderate and occurred mainly while doses were increasing. The paper reported these percentages:
| Event | 5 mg | 10 mg | 15 mg | Placebo |
|---|---|---|---|---|
| Nausea | 24.6% | 33.3% | 31.0% | 9.5% |
| Diarrhea | 18.7% | 21.2% | 23.0% | 7.3% |
| Constipation | 16.8% | 17.1% | 11.7% | 5.8% |
| Vomiting | 8.3% | 10.7% | 12.2% | 1.7% |
| Stopped because of an adverse event | 4.3% | 7.1% | 6.2% | 2.6% |
SURMOUNT-1 compared tirzepatide with placebo, not with semaglutide. That distinction is easy to miss when the two medications appear in the same conversation. A different head-to-head trial is needed to compare them directly.
What later studies added—and the limits they exposed
A 2025 body-composition substudy used DXA, a scan that estimates fat and lean tissue, in just 160 participants. About 75% of the weight lost was fat mass and 25% was lean mass in both the tirzepatide and placebo groups. Because this was a small slice of the original trial, it adds context rather than a guarantee about body composition (Look et al., Diabetes, Obesity and Metabolism 2025).
A separate analysis looked only at selected participants who stayed fairly close to the trial plan and had lost at least 5%. Median time to a plateau ranged from 24.3 to 36.1 weeks across starting BMI groups, and most had reached the study's plateau definition by week 72. That was an after-the-fact analysis, not a test of whether changing dose breaks a plateau (Horn et al., Clinical Obesity 2025). The tirzepatide before-and-after timeline explains what the studies measured at each stage without relying on photos.
SURMOUNT-4 later tested continuation more directly. After a 36-week tirzepatide lead-in, 670 adults were assigned by chance either to continue or switch to placebo. During the next 52 weeks, the switch group regained 14.0% of its week-36 weight on average, while the continuation group lost another 5.5% (Aronne et al., JAMA 2024). SURMOUNT-1 alone could not answer that maintenance question.
As of September 9, 2026, the day this article was written, an August 11, 2026 JACC paper had added a new look at SURMOUNT-1 blood samples. In 392 selected participants who completed treatment, estimated reductions relative to placebo in hsCRP, a blood marker of inflammation, ranged from 36.9% to 54.6% across doses. This was a post hoc analysis, meaning the question was asked after trial data existed; it measured biomarkers, not heart attacks or strokes (Sattar et al., JACC 2026).
The larger caution is simple. Participants had no diabetes, followed a controlled protocol, and received structured lifestyle support. The trial was company-funded. Its averages should not be stretched into a personal promise or a result for a population it did not study.
What the trial cannot say about a compounded version
SURMOUNT-1 studied branded tirzepatide made and handled under its trial protocol. It did not test Promise's compounded formulation. Through Promise, tirzepatide is dispensed as a compounded medication, which is different from an FDA-approved product: the formulation offered here is not FDA-approved. The FDA explains that it does not verify a compounded drug's safety, effectiveness, or quality before marketing.
A licensed provider may still prescribe a compounded formulation; that decision is between the patient and doctor. At Promise, a licensed provider reviews every request, and not everyone qualifies.
The useful way to read one trial result
SURMOUNT-1 gives a solid reference point when the population, dose, time, and comparison group stay attached to the number. Strip those away and 20.9% becomes advertising instead of evidence. Kept in context, the result can support a calm conversation about expected ranges, side effects, and what an individual plan will measure. For what has changed since the trial, the quarterly tirzepatide news update carries the dated list.