Did SURPASS-2 have a formal extension study?

No. SURPASS-2 was a 40-week trial with a 4-week safety follow-up period. No pre-specified extension was included in the protocol, and no separate extension study has been published as of this review.

What happens when patients stop tirzepatide after SURPASS-2?

SURPASS-2 itself did not track off-treatment outcomes. Data from the SURMOUNT-1 obesity trial show that patients who discontinued tirzepatide regained approximately 60-70% of lost weight within one year. Glycemic parameters also drifted back toward baseline.

Is tirzepatide's A1C benefit durable during ongoing treatment?

Yes, based on evidence across the SURPASS program. Trials lasting up to 52 weeks showed sustained glycemic improvement without a wearing-off effect during active treatment.

Why was semaglutide 1 mg used as the comparator instead of 2.4 mg?

SURPASS-2 was designed as a type 2 diabetes trial. Semaglutide 1 mg (Ozempic) is the maximum approved dose for diabetes. The 2.4 mg dose (Wegovy) is approved for obesity, and using it would have changed the regulatory and clinical framing of the comparison.

Did any new safety signals emerge after the SURPASS-2 trial period?

Post-marketing surveillance across GLP-1 receptor agonists has flagged gastroparesis-like symptoms, and a 2023 JAMA study identified elevated risks of pancreatitis and bowel obstruction. These signals are class-level findings, not specific to SURPASS-2, but they underscore the need for longer follow-up.

Will SURPASS-CVOT answer the long-term durability question?

Partially. SURPASS-CVOT runs for approximately 54 months and will provide extended safety and cardiovascular outcome data. It compares tirzepatide against dulaglutide, not semaglutide, so it will not directly extend the SURPASS-2 comparison.

How does regression to the mean affect SURPASS-2 results?

Regression to the mean likely inflated absolute A1C reductions in all arms. The between-group comparisons (tirzepatide vs semaglutide) are less affected because both arms experience similar regression. The estimated treatment differences remain valid.

Should patients expect permanent metabolic changes from tirzepatide?

Current evidence does not support permanent metabolic resetting. Both tirzepatide and semaglutide appear to require ongoing administration to maintain their glycemic and weight effects. This is consistent with the pharmacology of incretin-based therapies.

Are there head-to-head data comparing tirzepatide to semaglutide 2.4 mg?

No published head-to-head trial compares tirzepatide at any dose to semaglutide 2.4 mg as of this review date. SURPASS-2 used semaglutide 1 mg, and no subsequent trial has addressed this specific comparison.

How do SURPASS-2 GI side effects compare to real-world experience?

Within the trial, nausea rates ranged from 17-24% with tirzepatide versus 18% with semaglutide 1 mg. Real-world reports suggest GI events may be more persistent in some patients than trial data indicate, possibly reflecting differences in dose titration speed and patient selection outside controlled settings.

SURPASS-2 Extension Data and What Happened After the Trial Ended

By HealthRX Medical Team

Published May 25, 2026Updated May 25, 2026Last reviewed May 25, 2026

At a glance

| Parameter | Detail | |---|---| | Trial | SURPASS-2 (NCT04143399) | | N | 1,879 randomized | | Intervention | Tirzepatide 5 mg, 10 mg, or 15 mg subcutaneous weekly | | Comparator | Semaglutide 1 mg subcutaneous weekly | | Duration | 40-week treatment period | | Primary endpoint | Change in HbA1c from baseline | | Key result | All three tirzepatide doses were superior to semaglutide 1 mg for A1C reduction (estimated differences: -0.15% to -0.45%) and body weight loss |

Why extension data matters for incretin trials

Trials that run 40 weeks answer one question well: does the drug work while patients take it? They cannot answer whether benefits persist, whether safety signals accumulate, or whether the metabolic improvements reflect durable physiological change versus pharmacologic suppression that reverses on withdrawal.

For SURPASS-2, these questions carry particular weight. The trial compared tirzepatide against semaglutide 1 mg, a dose now considered submaximal for weight management since semaglutide 2.4 mg (Wegovy label) became the standard weight-loss dose. Any durability claims from SURPASS-2 must be read against this design constraint.

What SURPASS-2 did and did not include

SURPASS-2 was a 40-week, open-label, phase 3 trial. Participants had type 2 diabetes inadequately controlled on metformin (baseline A1C ~8.3%), and were randomized to one of three tirzepatide doses or semaglutide 1 mg. The trial did not include a pre-specified extension period. There was no protocol-defined follow-up after week 40 to track what happened when treatment stopped.

This is a meaningful gap. The STEP 1 extension data for semaglutide 2.4 mg in obesity showed that participants regained roughly two-thirds of lost weight within one year of stopping treatment. Without a parallel off-treatment follow-up for SURPASS-2, clinicians are left extrapolating from other GLP-1 and GIP/GLP-1 trials.

The safety follow-up window

SURPASS-2 included a post-treatment safety follow-up of approximately 4 weeks. This period captured adverse events after the last dose but was too short to assess metabolic rebound, weight trajectory, or whether gastrointestinal side effects resolved promptly. The 4-week window is standard for regulatory filings but tells us almost nothing about durability.

Durability signals from the broader SURPASS program

While SURPASS-2 itself lacked extension data, other trials in the program provide indirect evidence.

SURPASS-1 through SURPASS-5 composite picture

Across the SURPASS program, A1C reductions with tirzepatide were consistent at 40 to 52 weeks. SURPASS-4 ran for 52 weeks and showed sustained A1C reduction in patients with established cardiovascular disease. SURPASS-3, comparing tirzepatide against insulin degludec, also demonstrated durable glycemic control over 52 weeks with continued treatment.

The key observation: glycemic and weight effects were maintained as long as patients stayed on therapy. No trial in the program showed a wearing-off effect during active treatment.

SURMOUNT-1 off-treatment data

The most direct evidence for what happens after stopping tirzepatide comes from SURMOUNT-1, which studied tirzepatide for obesity (without diabetes). After 72 weeks of treatment, participants who discontinued tirzepatide regained a substantial portion of lost weight over the following year. A1C and metabolic markers also drifted back toward baseline, though not fully.

This pattern mirrors semaglutide discontinuation data and suggests a class-level phenomenon: incretin-based therapies suppress appetite and improve metabolic parameters through ongoing pharmacologic action, not through permanent metabolic resetting.

The Durability Assessment Framework for Incretin Trials

To evaluate whether an incretin trial's results predict long-term clinical value, we apply a four-axis assessment across the evidence base:

| Axis | Question | SURPASS-2 Status | |---|---|---| | On-treatment plateau | Did efficacy stabilize or continue improving at trial end? | A1C and weight curves were still separating at week 40, suggesting the 40-week snapshot may underestimate peak effect | | Off-treatment trajectory | What happened after drug withdrawal? | No data from SURPASS-2 itself. SURMOUNT-1 off-treatment data shows ~60-70% weight regain within 1 year | | Dose-response persistence | Did higher doses show more durable effects? | At week 40, dose-response for A1C was clear (5 mg < 10 mg < 15 mg). Whether higher doses confer more durable off-treatment benefit is unknown | | Safety signal evolution | Did adverse events plateau or accumulate over time? | GI side effects (nausea, diarrhea, vomiting) peaked during dose escalation and declined by week 20. No progressive safety signal observed through week 40 |

This framework highlights a critical gap: SURPASS-2 scores well on on-treatment metrics but has no data for the two axes that matter most for chronic disease management, specifically off-treatment trajectory and long-term safety signal evolution.

Regression-to-mean considerations

Baseline A1C in SURPASS-2 averaged 8.28%. Regression to the mean, the statistical tendency for extreme baseline values to move toward the population average on repeat measurement, likely contributed some portion of the observed A1C improvement across all arms, including the semaglutide comparator.

The trial's use of an active comparator partially mitigates this concern. Because both arms would experience similar regression effects, the between-group difference (tirzepatide vs semaglutide) is more reliable than the within-group change from baseline. The estimated treatment differences of -0.15% (5 mg), -0.39% (10 mg), and -0.45% (15 mg) versus semaglutide 1 mg are adjusted for this.

Still, the absolute A1C reductions reported in each arm (ranging from -1.86% to -2.46%) should not be directly projected as the expected clinical effect in a broader population with lower baseline A1C.

Safety signals that emerged later

Thyroid signal

Tirzepatide carries a boxed warning for thyroid C-cell tumors based on rodent findings, consistent with other GLP-1 receptor agonists. SURPASS-2's 40-week duration was insufficient to detect medullary thyroid carcinoma in humans, where the latency period is measured in years. Post-marketing surveillance remains the only viable detection mechanism for this signal.

Gastrointestinal events in clinical practice

Within SURPASS-2, GI adverse events were more common with tirzepatide (nausea: 17-24% across doses) compared to semaglutide 1 mg (18%). The rates were broadly comparable, though the 15 mg tirzepatide dose had slightly higher discontinuation rates due to GI complaints.

Post-marketing reports and real-world data have since flagged gastroparesis-like symptoms with GLP-1 receptor agonists more broadly. The 2023 JAMA report on GLP-1 associated gastrointestinal events found elevated risks of pancreatitis, bowel obstruction, and gastroparesis compared with bupropion-naltrexone. While not specific to tirzepatide, these signals warrant longer follow-up than any SURPASS trial provided.

Pancreatitis and pancreatic safety

Pancreatitis events in SURPASS-2 were rare and numerically balanced between arms. The tirzepatide prescribing information advises monitoring for signs and symptoms. Longer-term registries and the ongoing SURPASS-CVOT will provide more definitive data on pancreatic safety.

The semaglutide 1 mg comparator problem

A persistent limitation in interpreting SURPASS-2's durability implications: the comparator dose. Semaglutide 1 mg (Ozempic) is approved for type 2 diabetes, but the 2.4 mg dose (Wegovy) produces substantially greater weight loss. The trial was designed to compare diabetes treatments, not to test the maximum possible incretin effect against tirzepatide.

For clinicians asking whether tirzepatide offers long-term advantages over maximally-dosed semaglutide, SURPASS-2 cannot answer that question. No head-to-head trial of tirzepatide versus semaglutide 2.4 mg has been published as of this review date. The practical implication: patients and prescribers should not interpret SURPASS-2 as evidence that tirzepatide is categorically superior to all semaglutide dosing regimens over the long term.

What SURPASS-CVOT will add

The SURPASS-CVOT trial (also called SURPASS-6 in some references) is a cardiovascular outcomes trial designed to run for approximately 54 months. It compares tirzepatide against dulaglutide, not semaglutide. When completed, it will provide the longest-duration safety and efficacy data for tirzepatide in type 2 diabetes.

SURPASS-CVOT will address several gaps left by SURPASS-2: cardiovascular event rates with long-term use, whether glycemic benefits are maintained beyond one year of continuous therapy, and whether any progressive safety signals emerge. Results are expected to inform label updates and clinical guideline positioning.

Clinical translation: what to tell patients

Given the absence of formal SURPASS-2 extension data, three practical points emerge:

Benefits require ongoing treatment. The available evidence across the SURPASS and SURMOUNT programs consistently shows that stopping tirzepatide leads to partial or substantial reversal of metabolic improvements. Patients should understand they are likely committing to long-term therapy.

The 40-week results are reliable for the on-treatment period. The primary trial data are methodologically sound for the question asked. Tirzepatide did outperform semaglutide 1 mg on A1C and weight during active treatment.

Longer-term safety data are still accumulating. The absence of multi-year follow-up means that rare adverse events, effects on bone density, effects on lean mass, and cardiovascular outcomes with tirzepatide remain incompletely characterized.

Limitations of this analysis

This review is constrained by the absence of a formal SURPASS-2 extension study. Inferences about post-trial outcomes rely on cross-trial extrapolation from SURMOUNT-1 and semaglutide discontinuation studies, which differ in patient population (obesity without diabetes vs type 2 diabetes). Real-world persistence and adherence data for tirzepatide are still maturing, and registry-level evidence may shift these conclusions as it accumulates.

Frequently asked questions

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References

Frías JP, Davies MJ, Rosenstock J, et al. Tirzepatide versus semaglutide once weekly in patients with type 2 diabetes. N Engl J Med. 2021;385(6):503-515. PubMed
Wilding JPH, Batterham RL, Davies M, et al. Weight regain and cardiometabolic effects after withdrawal of semaglutide. Diabetes Obes Metab. 2022;24(8):1553-1564. PubMed
Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide once weekly for the treatment of obesity. N Engl J Med. 2022;387(3):205-216. PubMed
Mounjaro (tirzepatide) prescribing information. Eli Lilly and Company. 2022. FDA Label
Wegovy (semaglutide) prescribing information. Novo Nordisk. 2023. FDA Label
Sodhi M, Rezaeianzadeh R, Kezouh A, Bhatt DL. Risk of gastrointestinal adverse events associated with glucagon-like peptide-1 receptor agonists for weight loss. JAMA. 2023;330(18):1795-1797. PubMed