Evidence section
Tirzepatide studies explained
Two pharmacists registered and practising in British Columbia read this page against the study pages and papers it lists and signed it. Their names are withheld from the site and held on file; their registration is confirmed on request.
Tirzepatide is the medicine behind Zepbound and Mounjaro. SURMOUNT trials tested it for weight management, SURPASS trials for type 2 diabetes, SUMMIT for a type of heart failure, and SURMOUNT-OSA for sleep apnea. This hub lists every tirzepatide study we have reviewed, including the two head-to-head trials against semaglutide. Each page reports the numbers as published and explains the study design in plain words.
What these studies show together
In every placebo-controlled trial here, average weight loss was larger with tirzepatide than with placebo, in adults with and without type 2 diabetes. A 2025 Cochrane review that pooled the placebo-controlled trials rated that finding moderate certainty. Evidence beyond weight is narrower: one trial in a specific form of heart failure, one diabetes trial in which heart events were a safety measure, one analysis in sleep apnea, and one three-year analysis in people with prediabetes. Stomach and bowel symptoms were the most common side effects in every trial that reported them.
The studies side by side
| Study | Who was studied | Compared with | Length | Main result, as reported |
|---|---|---|---|---|
| SURMOUNT-1 | 2539 adults without diabetes | Placebo | 72 weeks | Weight -15.0%, -19.5% and -20.9% (5, 10 and 15 mg) vs -3.1% |
| SURMOUNT-2 | 938 adults with type 2 diabetes and a BMI of 27 or more | Placebo | 72 weeks | Weight -12.8% (10 mg) and -14.7% (15 mg) vs -3.2% |
| SURMOUNT-1, three years | 1032 SURMOUNT-1 participants with prediabetes | Placebo | 176 weeks, then 17 weeks off | Weight -12.3% to -19.7% vs -1.3%; type 2 diabetes diagnosed in 1.3% vs 13.3% |
| SURMOUNT-5 | 751 adults without type 2 diabetes | Semaglutide 1.7 or 2.4 mg, open-label | 72 weeks | Weight -20.2% vs -13.7% |
| SURPASS-2 | 1879 adults with type 2 diabetes | Semaglutide 1 mg, open-label | 40 weeks | HbA1c -2.01 to -2.30 points vs -1.86; weight 1.9 to 5.5 kg lower |
| SURPASS-4 | 2002 adults with type 2 diabetes and high heart risk | Insulin glargine, open-label | 52 to 104 weeks | HbA1c -2.43 and -2.58 points vs -1.44; major heart events HR 0.74 (0.51 to 1.08) |
| SUMMIT | 731 adults with heart failure with preserved ejection fraction and a BMI of 30 or more | Placebo | Median 104 weeks | Heart death or worsening heart failure 9.9% vs 15.3%, HR 0.62 (0.41 to 0.95) |
| SURMOUNT-OSA | 469 adults with obesity and moderate to severe sleep apnea | Placebo | 52 weeks | Systolic blood pressure 7.9 mmHg (no PAP) and 4.3 mmHg (using PAP) lower than placebo |
| Cochrane review | 7111 adults in 9 randomized trials | Mainly placebo | 12 to 18 months (8 trials) | Weight 16.03 percentage points lower than placebo, moderate certainty |
What is consistent
Weight loss with tirzepatide was larger than with placebo in each trial, and in the trials that tested more than one dose, the higher doses produced larger average losses. The side effects were mainly nausea, diarrhea, vomiting and other stomach and bowel symptoms, mostly mild to moderate and concentrated while the dose was being raised. More people stopped treatment because of side effects on tirzepatide than on placebo: for example 4.3% to 7.1% versus 2.6% in SURMOUNT-1, and a risk ratio of 2.06 in the Cochrane review, rated low certainty.
Comparisons with semaglutide
Two trials compared tirzepatide with semaglutide directly, and they answer different questions. SURPASS-2 used semaglutide 1 mg, a diabetes dose, in people with type 2 diabetes, with HbA1c as the main outcome. SURMOUNT-5 used the highest dose each person could tolerate of each medicine in people without type 2 diabetes, with weight as the main outcome, and found -20.2% with tirzepatide and -13.7% with semaglutide at 72 weeks. Both trials were open-label, and SURMOUNT-5 was funded by the maker of tirzepatide. One trial in one population is not a general ranking of the two medicines, and SURMOUNT-5 did not measure heart events.
Heart, sleep apnea and diabetes prevention
SUMMIT found fewer of the combined outcome of heart death or worsening heart failure with tirzepatide, driven by fewer worsening heart failure events; it did not show fewer deaths. SURPASS-4 found no increase in major heart events compared with insulin glargine, and it did not show a heart benefit either. The Cochrane review judged that tirzepatide likely made little to no difference to major heart events or death over 12 to 18 months. Among the studies here, there is no completed heart outcome trial of tirzepatide in people living with obesity without heart failure. In people with prediabetes, three years of tirzepatide was followed by far fewer diagnoses of type 2 diabetes than placebo. In sleep apnea, blood pressure fell more with tirzepatide, which is a marker of risk rather than a measured reduction in heart attacks or strokes.
What these studies cannot tell you
All but one of these pages were written from the published abstract, so detailed safety tables, dropouts by group and some confidence intervals were not available. Every trial page that states its funding names the manufacturer, and the Cochrane review found major manufacturer involvement in all nine trials it included. The longest treatment period here is 176 weeks, in the prediabetes group. What happens after tirzepatide is stopped is covered in what happens when weight-management medicines are stopped. For what tirzepatide is authorized for in Canada and how it is paid for, see tirzepatide in Canada.
This summary draws only on the study pages listed below and adds no figures that are not on them. Written 2026-09-23; reviewed by two pharmacists registered in British Columbia, 2026-09-23.
Studies in this section (9)
Tirzepatide versus insulin glargine in higher-risk diabetes: SURPASS-4
SURPASS-4 compared tirzepatide with insulin glargine in adults with type 2 diabetes and high heart risk. Plain-language results for Canadian readers.
Tirzepatide versus semaglutide 1 mg in type 2 diabetes: SURPASS-2
SURPASS-2 compared three tirzepatide doses with semaglutide 1 mg in adults with type 2 diabetes over 40 weeks. Plain-language results for Canadian readers.
Tirzepatide for weight loss in adults without diabetes: SURMOUNT-1
SURMOUNT-1 tested tirzepatide 5, 10 and 15 mg against placebo for 72 weeks in 2539 adults without diabetes. Plain-language results for Canadian readers.
Tirzepatide for weight loss in type 2 diabetes: SURMOUNT-2
SURMOUNT-2 tested tirzepatide 10 and 15 mg against placebo for 72 weeks in 938 adults with type 2 diabetes. Plain-language results for Canadian readers.
Three years of tirzepatide in adults with prediabetes: SURMOUNT-1
In SURMOUNT-1 participants with prediabetes, three years of tirzepatide kept weight down and fewer developed type 2 diabetes. Plain summary for Canada.
Tirzepatide for heart failure with a higher body weight: SUMMIT
SUMMIT tested tirzepatide in 731 adults with heart failure with preserved ejection fraction and obesity. Plain-language heart event results for Canada.
Tirzepatide versus semaglutide head to head: SURMOUNT-5
SURMOUNT-5 compared tirzepatide with semaglutide directly for 72 weeks in 751 adults without diabetes. Plain-language weight results for Canadian readers.
What a Cochrane review says about tirzepatide for weight loss
A 2025 Cochrane review pooled 9 tirzepatide trials with 7111 adults. Plain-language summary of weight, side effect and heart results for Canadian readers.
Tirzepatide, sleep apnea and blood pressure: SURMOUNT-OSA
A planned SURMOUNT-OSA analysis reports how tirzepatide changed blood pressure in adults with sleep apnea and obesity. Plain-language summary for Canada.
Other evidence sections
How to read these pages
Every page in this section explains one published study. The numbers are reported as the researchers published them, with a link to the paper on PubMed. Pages say what a study cannot tell you and never rank one medicine against another. They are education, not medical advice. For how a medicine is used and paid for in Canada, see medicines, public drug coverage by province and compare services.
Reviewed and signed by two pharmacists registered in British Columbia, 2026-09-23.