Tirzepatide Clinical Trials: Results, Limitations and Research Gaps
Tirzepatide clinical trials have examined its effects on blood glucose, body weight, and cardiovascular outcomes across different patient populations. The SURPASS programme studied adults with type 2 diabetes, while the SURMOUNT programme investigated weight management in people with overweight or obesity. Later research has expanded the evidence base to include cardiovascular outcomes and longer-term questions.
However, trial results need careful interpretation. A study’s findings depend on its participants, comparison group, duration, endpoints, and statistical design. Understanding these factors helps readers distinguish demonstrated outcomes from unanswered research questions.
How the Tirzepatide Clinical Trial Programme Developed
Tirzepatide is a dual agonist of the glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) receptors. These pathways are involved in glucose regulation, appetite, and energy balance.
Its clinical development has involved several related but distinct research programmes.
- SURPASS: Evaluated glycaemic outcomes and safety in adults with type 2 diabetes.
- SURMOUNT: Investigated weight-related outcomes in people with overweight or obesity, including participants without diabetes.
- SURPASS-CVOT: Compared cardiovascular outcomes with those observed with dulaglutide in adults with type 2 diabetes and established cardiovascular disease.
These programmes address different questions. A study showing improved glycaemic control does not, by itself, establish a reduction in cardiovascular events. Similarly, a weight-management trial cannot automatically answer questions about long-term outcomes in every population.
SURPASS Trials: Evidence in Type 2 Diabetes
The SURPASS programme examined tirzepatide across a range of clinical settings, including use as a single therapy and in comparison with other glucose-lowering treatments.
Researchers commonly measured glycated haemoglobin (HbA1c), a marker of average blood glucose over approximately two to three months. Trials also examined body-weight changes and adverse events.
SURPASS-2: Comparison with semaglutide
Published in 2021, SURPASS-2 was a randomised, active-controlled trial involving adults with type 2 diabetes whose blood glucose was not adequately controlled with metformin alone.
The study compared three tirzepatide groups with semaglutide at 1 mg over 40 weeks. The primary endpoint was the change in HbA1c from baseline.
Tirzepatide groups achieved greater average reductions in HbA1c and body weight than the semaglutide comparison group under the conditions studied. The trial provided direct comparative evidence for these outcomes in this specific population.
There is an important qualification: the semaglutide comparator was 1 mg, and the study was designed around people with type 2 diabetes. Its results should not be treated as a direct comparison of every available dose or every indication of either medicine.
The findings also illustrate why researchers must read the methods and population details rather than relying on headlines that describe one treatment as universally more effective.
What the SURPASS programme adds
Across the wider programme, studies compared tirzepatide with placebo, insulin therapies, and other glucose-lowering medicines. These comparisons helped researchers assess its performance under different treatment conditions.
The comparator matters. A placebo-controlled study asks whether an intervention differs from placebo, while an active-controlled study asks how it compares with another treatment. The answers are not interchangeable.
The US Food and Drug Administration’s Mounjaro Drug Trials Snapshot provides an overview of pivotal diabetes trials and their HbA1c endpoints.
SURMOUNT-1: Weight-Related Outcomes Over 72 Weeks
SURMOUNT-1 was a major randomised, double-blind, placebo-controlled trial published in 2022. It enrolled 2,539 adults with obesity, or overweight with at least one weight-related complication, who did not have diabetes.
Participants were assigned to tirzepatide at different target doses or placebo, alongside lifestyle intervention. The primary endpoint was percentage change in body weight at 72 weeks.
The reported mean weight changes were:
| Study group | Mean body-weight change at week 72 |
|---|---|
| Tirzepatide 5 mg | −15.0% |
| Tirzepatide 10 mg | −19.5% |
| Tirzepatide 15 mg | −20.9% |
| Placebo | −3.1% |
These are average results for the trial groups, not predictions for every participant. Individual outcomes varied, and the findings apply to the study’s population, protocol, and follow-up period.
SURMOUNT-1 demonstrated substantial average weight reduction compared with placebo over the trial period. It did not establish that all participants would experience the same outcome or that the results automatically apply to people with different health profiles.
Researchers also assessed adverse events. Gastrointestinal effects, including nausea, diarrhoea, and vomiting, were among the commonly reported events. As with other clinical trials, understanding tolerability requires examining both the frequency and severity of events, as well as discontinuations and the way safety data were collected.
SURMOUNT-5: Direct Comparison with Semaglutide
Comparisons across separate trials can be misleading because study populations, protocols, follow-up periods, and endpoints may differ. Direct head-to-head studies can reduce some of these uncertainties.
SURMOUNT-5, published in 2025, compared tirzepatide with semaglutide in 751 adults with obesity who did not have type 2 diabetes. It was an open-label, randomised trial with a 72-week primary endpoint.
The reported least-squares mean changes in body weight at week 72 were:
- Tirzepatide: −20.2%.
- Semaglutide: −13.7%.
The trial also reported greater average reductions in waist circumference in the tirzepatide group. Gastrointestinal adverse events were common in both groups and occurred primarily during dose escalation.
Because this was a direct comparison, the results offer stronger evidence about the relative effects of the two treatments for the outcomes studied than a comparison of separate placebo-controlled trials would provide.
Nevertheless, the findings remain specific to the study’s population, treatment regimens, and endpoints. They do not settle every question about comparative effectiveness, long-term outcomes, or how the treatments perform in populations not represented by the trial.
SURPASS-CVOT: What Cardiovascular Research Found
Blood glucose and body-weight changes are important clinical outcomes, but they do not automatically prove that a treatment reduces heart attacks, strokes, or cardiovascular deaths. These questions require studies designed to measure clinical events.
SURPASS-CVOT, published in December 2025, addressed this issue by comparing tirzepatide with dulaglutide in adults with type 2 diabetes and established atherosclerotic cardiovascular disease.
The double-blind trial randomised more than 13,000 participants. Its primary endpoint was a composite of cardiovascular death, myocardial infarction, or stroke.
The primary outcome occurred in:
- 12.2% of participants assigned to tirzepatide.
- 13.1% of participants assigned to dulaglutide.
The hazard ratio was 0.92, with a 95.3% confidence interval of 0.83 to 1.01. The study met its prespecified criterion for noninferiority, but it did not establish statistical superiority over dulaglutide for the primary endpoint.
This distinction is central to interpreting the result. Noninferiority means the results met a predefined standard for ruling out an unacceptable loss of effect relative to the comparator. It does not mean that superiority was demonstrated.
The trial also found that gastrointestinal adverse events were more common with tirzepatide, although overall adverse-event patterns appeared similar between groups.
The result contributes important cardiovascular safety and comparative-outcome evidence. It should not be misrepresented as proof that tirzepatide is superior to all other treatments or that it produces the same cardiovascular effects in every patient population.
How Researchers Should Interpret Trial Results
Clinical trial headlines often focus on a single percentage or statistical result. A more useful assessment considers several features together.
1. Study population
Were participants living with type 2 diabetes, obesity without diabetes, or established cardiovascular disease? These groups have different baseline characteristics and risks.
Results from one population should not automatically be generalised to another.
2. Comparator
A placebo group provides a different benchmark from an active treatment group. For example, SURMOUNT-1 compared tirzepatide with placebo, while SURMOUNT-5 compared it directly with semaglutide.
A larger difference from placebo cannot be used on its own to rank two medicines tested in different trials.
3. Endpoint
HbA1c, percentage weight change, and major cardiovascular events measure different outcomes. A treatment may perform well on one endpoint without necessarily demonstrating an advantage on another.
Researchers should identify the primary endpoint before interpreting secondary findings.
4. Follow-up duration
A result measured at 40, 72, or 104 weeks answers a question about that period. Longer follow-up can provide additional information about durability and less common safety outcomes, but it cannot be assumed from shorter studies.
5. Statistical uncertainty
Effect estimates should be considered alongside confidence intervals, sample size, and the prespecified statistical analysis plan.
A result that appears numerically favourable may still have uncertainty that prevents a firm conclusion about superiority. Likewise, statistical significance does not automatically establish that an effect is clinically important.
6. Discontinuations and missing data
Participants may discontinue a trial or miss assessments. The statistical approach to these events can affect how results are estimated.
Researchers should review the analysis population, handling of missing data, and assumptions used in the analysis rather than treating every reported estimate as a simple measurement of all participants’ experiences.
Safety Findings and the Limits of Trial Evidence
Clinical trials collect safety information, including adverse events, serious adverse events, treatment discontinuations, and selected laboratory findings. However, a trial’s ability to detect a risk depends on its size, duration, participant selection, and monitoring procedures.
Gastrointestinal adverse events have been prominent in tirzepatide studies. The frequency and severity of reported events vary across trials and treatment settings, so comparisons should be made using the original study reports and product-specific information.
Trial populations may also exclude people with certain conditions or other characteristics. As a result, the evidence may be less complete for groups that were underrepresented or excluded.
Post-authorisation safety monitoring and longer-term studies can add information that is difficult to obtain from pre-approval trials alone. They can also help identify uncommon events or outcomes that emerge over longer periods.
For current regulatory information, consult the relevant jurisdiction’s official product information. For example, the US prescribing information for Zepbound on DailyMed describes clinical studies and selected safety findings for that product.
Research Gaps: What Remains to Be Answered?
Despite the substantial clinical evidence, several areas continue to warrant investigation.
Long-term durability: Additional follow-up can help clarify how outcomes change over multiple years and what happens after treatment discontinuation.
Broader populations: Evidence may be less certain for people whose characteristics differ from those included in pivotal trials, including some older adults and people with complex health conditions.
Comparative outcomes: Direct trials answer specific questions, but further comparisons may be needed for other populations, treatment settings, endpoints, and longer-term outcomes.
Cardiovascular and other clinical events: Studies designed to measure hard clinical outcomes are needed to answer questions that cannot be resolved by changes in HbA1c or body weight alone.
Real-world effectiveness: Observational research can help examine how outcomes and discontinuations look in routine clinical settings. Such studies also need careful interpretation because differences between treatment groups can introduce confounding.
Safety over time: Larger populations and longer observation may provide more information about uncommon adverse events and outcomes that are difficult to assess in shorter controlled trials.
These research gaps do not erase the findings of completed studies. They define where the current evidence is strong, where it is specific to certain circumstances, and where further investigation could improve understanding.
Frequently Asked Questions
What are the main tirzepatide clinical trials?
Major programmes include SURPASS, which studied outcomes in type 2 diabetes; SURMOUNT, which investigated weight-related outcomes; and SURPASS-CVOT, which compared cardiovascular outcomes with dulaglutide in adults with type 2 diabetes and established cardiovascular disease.
What did SURMOUNT-1 find?
At 72 weeks, mean body-weight changes were −15.0%, −19.5%, and −20.9% in the 5 mg, 10 mg, and 15 mg tirzepatide groups, respectively, compared with −3.1% with placebo. These were trial averages for adults with obesity or overweight and weight-related complications who did not have diabetes.
Did SURPASS-CVOT prove that tirzepatide was superior to dulaglutide?
No. It demonstrated noninferiority for the primary composite cardiovascular endpoint. The superiority test was not statistically significant.
Can results from separate trials be compared directly?
Not reliably without considering differences in population, design, comparator, endpoint, and follow-up. Head-to-head randomised trials generally provide stronger direct comparative evidence for their specified outcomes.
What are the main limitations of tirzepatide trials?
Limitations may include restricted eligibility criteria, finite follow-up, missing data, reliance on selected endpoints, and limited power to detect uncommon or long-term safety outcomes. The specific limitations vary by study.
Conclusion
Tirzepatide clinical trials provide evidence across glycaemic control, body-weight reduction, and cardiovascular outcomes. SURPASS-2 offers direct comparative evidence for glycaemic and weight-related outcomes against semaglutide 1 mg in adults with type 2 diabetes. SURMOUNT-1 demonstrated substantial average weight reduction compared with placebo, while SURMOUNT-5 directly compared tirzepatide with semaglutide in adults with obesity without diabetes. SURPASS-CVOT showed noninferiority to dulaglutide for its primary cardiovascular endpoint, without demonstrating superiority.
The most accurate interpretation starts with the research question each trial was designed to answer. Population, comparator, endpoint, follow-up, and statistical uncertainty all matter. Further long-term, comparative, and real-world research can help clarify the questions that completed trials cannot fully resolve.
Research and education disclaimer: This article summarises clinical research for educational purposes and is not medical advice or a treatment recommendation. Readers should consult qualified healthcare professionals and current official product information for individual medical decisions.