The main finding
In one sentence: In adults with type 2 diabetes and a higher body weight, 72 weeks of weekly tirzepatide led to an average weight change of -12.8% with 10 mg and -14.7% with 15 mg, compared with -3.2% with placebo.
Group averages, not an individual prediction. A trial result describes what happened to a defined group over a defined time.
On this page
Why this study matters
People with type 2 diabetes often find weight loss harder, and results from trials in people without diabetes may not apply to them. SURMOUNT-2 tested tirzepatide (Zepbound, Mounjaro) specifically in adults with type 2 diabetes. It is the diabetes counterpart to SURMOUNT-1, and it is the trial to look at if you or someone you care for has both diabetes and a higher body weight.
Who was in the study
The trial randomized 938 adults aged 18 or older with a body mass index, or BMI, of 27 or higher and type 2 diabetes with an HbA1c of 7 to 10%. BMI is a number that relates weight to height. HbA1c is a blood test that reflects average blood sugar over about three months.
Of the 1514 people assessed, 938 were enrolled between 29 March 2021 and 10 April 2023 in seven countries. Their average age was 54.2 years, 51% were female, 76% were White and 60% were Hispanic or Latino. At the start, average weight was 100.7 kg, average BMI was 36.1 and average HbA1c was 8.02%. The trial lasted 72 weeks.
What the researchers did
This was a phase 3, double-blind, randomized, placebo-controlled trial. Randomized means people were assigned by chance. Double-blind means participants, investigators and the sponsor did not know who received which treatment. A placebo is an injection that looks the same but contains no medicine.
People were split into three equal groups: weekly tirzepatide injections at 10 mg (312 people) or 15 mg (311 people), or placebo (315 people), for 72 weeks. The two primary outcomes were the percentage change in body weight from the start and the share of people who lost at least 5% of their weight.
The trial used a treatment-regimen estimand in the intention-to-treat population. An estimand is a precise statement of what the trial measures. Here it means everyone randomized was counted, whether or not they stopped treatment or needed extra diabetes medicine during the trial.
What they found
At week 72, average weight change was -12.8% with tirzepatide 10 mg, -14.7% with 15 mg and -3.2% with placebo (R32-C49). Compared with placebo, the difference was -9.6 percentage points for 10 mg (95% CI -11.1 to -8.1) and -11.6 percentage points for 15 mg (95% CI -13.0 to -10.1). A confidence interval, or CI, is the range within which the true difference most likely sits.
| Outcome at 72 weeks | Tirzepatide 10 mg | Tirzepatide 15 mg | Placebo |
|---|---|---|---|
| Average weight change | -12.8% | -14.7% | -3.2% |
| Difference vs placebo (95% CI) | -9.6 points (-11.1 to -8.1) | -11.6 points (-13.0 to -10.1) | Reference |
| Lost at least 5% of weight | 79 to 83% across both doses | 79 to 83% across both doses | 32% |
Between 79% and 83% of people on tirzepatide lost at least 5% of their weight, compared with 32% on placebo. The abstract does not separate the two doses for this measure.
Side effects and people who stopped
The most common side effects with tirzepatide were stomach and bowel symptoms, including nausea, diarrhea and vomiting. Most were mild to moderate. Few led to stopping treatment, which the abstract reports as under 5%, without giving a figure for each group. Serious adverse events were reported by 68 people (7%) overall. Two people in the tirzepatide 10 mg group died; the investigators judged the deaths not to be related to the study treatment. The published summary we reviewed does not report the overall number of people who stopped treatment in each group.
What this study does not tell you
- Everyone had type 2 diabetes. The results do not describe adults without diabetes, and they should not be merged with SURMOUNT-1.
- The exact percentage of people stopping because of side effects in each group is not in the summary we reviewed.
- The trial lasted 72 weeks. Rare and longer-term harms cannot be judged from it, and it does not show what happens after the medicine stops.
- Percentages from this trial should not be placed next to numbers from other medicines' trials to rank them.
- We reviewed the abstract only, so details of lifestyle support and blood sugar results were not checked.
- The trial was funded by the manufacturer.
What it means in Canada
For Canadian readers living with type 2 diabetes, SURMOUNT-2 is the main trial showing how tirzepatide affected weight in that group over 72 weeks. It does not describe how the medicine is prescribed or paid for here. See tirzepatide in Canada, public drug coverage by province and compare services.
Common questions
How much weight did people with type 2 diabetes lose on tirzepatide in SURMOUNT-2?
At 72 weeks, average weight change was -12.8% with tirzepatide 10 mg and -14.7% with 15 mg, compared with -3.2% with placebo.
Why is weight loss in SURMOUNT-2 lower than in SURMOUNT-1?
The two trials enrolled different people. SURMOUNT-2 included only adults with type 2 diabetes, and the two results should not be directly compared or merged.
How many people stopped tirzepatide because of side effects in SURMOUNT-2?
The abstract reports that few events led to stopping treatment, under 5%, but does not give the exact figure for each group.
Related reading
Other studies in this library that bear on the same question.
Tirzepatide for weight loss in adults without diabetes: SURMOUNT-1
Tirzepatide versus semaglutide 1 mg in type 2 diabetes: SURPASS-2
STEP 2: semaglutide for weight loss in type 2 diabetes
Tirzepatide versus semaglutide head to head: SURMOUNT-5
Tirzepatide versus insulin glargine in higher-risk diabetes: SURPASS-4
Source
Original paper: W Timothy Garvey, SURMOUNT-2, Lancet (London, England), 2023. PubMed: https://pubmed.ncbi.nlm.nih.gov/37385275/. DOI: https://doi.org/10.1016/S0140-6736(23)01200-X. Funding: The trial was funded by Eli Lilly and Company. How we summarized it: abstract and extracted data.
This page explains a published study. It is not medical advice and does not describe whether a medicine is right for you. Talk to your doctor, nurse practitioner or pharmacist about your own situation. Reviewed and signed by two pharmacists registered in British Columbia, 2026-09-18.
Evidence records behind this page
Each record is a row in the clinical evidence file, taken from the published paper named above. The caution column is the limit the researcher recorded for that number.
This table scrolls sideways.
| Record | What the paper reports | Type | Population | Caution | Source |
|---|---|---|---|---|---|
| R32-C49 | In SURMOUNT-2, adults with type 2 diabetes and overweight or obesity had average weight changes of -12.8% with tirzepatide 10 mg, -14.7% with 15 mg and -3.2% with placebo over 72 weeks. | direct evidence | Adults with BMI at least 27 and T2D; HbA 1c 7 to 10% | T2D population; abstract-only extraction; exact arm-specific discontinuation rates not extracted. | PubMed 37385275 |