SURMOUNT-4 Trial: What Tirzepatide Withdrawal Teaches Us About Long-Term Weight Management

What SURMOUNT-4 Actually Measured

SURMOUNT-4 was designed to answer one specific question: what happens to body weight when patients stop tirzepatide after achieving meaningful initial losses? In the 36-week open-label lead-in, all 783 enrolled participants received tirzepatide titrated to their maximum tolerated dose (10 mg or 15 mg). Mean weight loss across that period reached 20.9% from baseline. Then 670 participants were randomized, with half continuing tirzepatide and half switching to placebo for 52 additional weeks. [1]

Participants who continued tirzepatide lost a further 5.5% of body weight by week 88. Those on placebo regained 14.8 percentage points, ending the trial at approximately 9.9% below their original baseline. That means roughly 70% of the hard-won weight loss from the lead-in period evaporated within a year of stopping the drug.

The JAMA 2024 publication reported a between-group difference of 21.1 percentage points in weight change at week 88 (P<0.001). [1] That gap is not a subtle statistical finding. Patients who stayed on drug and patients who stopped it diverged at a rate visible within eight weeks of randomization.

The trial did not evaluate what happens if patients return to tirzepatide after a gap, nor did it test dose tapering as an exit strategy. Those are open questions the data cannot yet answer.

SURMOUNT-1: Where the Peak Efficacy Numbers Come From

SURMOUNT-1 (N=2,539) remains the foundational efficacy dataset for tirzepatide in adults with obesity or overweight without type 2 diabetes. Published in the New England Journal of Medicine in 2022, it tested three doses (5 mg, 10 mg, 15 mg) against placebo over 72 weeks. [2]

Mean weight reductions were 15.0%, 19.5%, and 20.9% for the 5 mg, 10 mg, and 15 mg groups respectively, versus 3.1% for placebo. At the 15 mg dose, 57% of participants achieved at least 20% body-weight loss. That figure had not been seen in any previous large-scale obesity drug trial.

The Zepbound FDA label, approved in November 2023, reflects these SURMOUNT-1 results and carries an indication for chronic weight management in adults with a BMI of 30 or greater, or BMI <27 with at least one weight-related comorbidity. [3]

Gastrointestinal adverse events (nausea, diarrhea, vomiting, constipation) were the most common reasons for discontinuation, occurring at higher rates with the 15 mg dose. Serious adverse event rates were similar across groups.

SURMOUNT-2: Tirzepatide in Type 2 Diabetes

SURMOUNT-2 enrolled 938 adults with both obesity and type 2 diabetes, the population excluded from SURMOUNT-1. Published in The Lancet in 2023, the trial ran 72 weeks and compared tirzepatide 10 mg and 15 mg against placebo. [4]

Mean weight loss reached 13.4% with 10 mg and 15.7% with 15 mg, compared with 3.3% for placebo. HbA1c reductions were 2.1 and 2.3 percentage points for the two active doses, and 38% of participants on 15 mg achieved an HbA1c below 5.7%, which is the normal range. No hypoglycemia related to tirzepatide as monotherapy was reported, though concomitant sulfonylurea or insulin use required dose adjustments.

Weight loss in a type 2 diabetes population is consistently lower than in non-diabetic populations across GLP-1 class trials. The gap between SURMOUNT-1 and SURMOUNT-2 efficacy figures parallels what was seen in the STEP program comparing STEP-1 (no T2D) with STEP-2 (T2D).

SURMOUNT-3: The Role of Prior Intensive Lifestyle Intervention

SURMOUNT-3 asked whether patients who first complete a rigorous lifestyle program lose more weight when they then add tirzepatide. Published in Nature Medicine in 2023, it enrolled 806 adults who underwent a 12-week intensive lifestyle intervention before randomization. Those who achieved at least 5% weight loss during that lead-in were then randomized to tirzepatide 15 mg or placebo for 72 weeks. [5]

From the point of randomization, tirzepatide produced an additional 18.4% reduction in body weight versus 2.5% for placebo. Measured from the study's start (before the lifestyle run-in), total weight loss in the tirzepatide arm reached 26.6%. That is the largest mean weight reduction reported in any published phase 3 obesity pharmacotherapy trial to date.

The study design makes direct comparison with other SURMOUNT arms difficult because the baseline population had already lost weight. Still, the data argues that lifestyle intervention before drug initiation does not diminish, and may somewhat augment, the pharmacological response to tirzepatide.

SURMOUNT-4 in Clinical Context: Chronic Disease Requires Chronic Treatment

The SURMOUNT-4 withdrawal data mirrors what was seen with semaglutide in the STEP-1 extension and in STEP-4 (a semaglutide withdrawal study not discussed in the key trial list but extensively referenced in obesity medicine literature). Across GLP-1 and dual GIP/GLP-1 agonist drug classes, the pattern is identical: substantial regain follows discontinuation, and that regain begins within weeks.

The American Association of Clinical Endocrinologists guidelines state that "obesity pharmacotherapy should be considered a long-term or lifelong treatment strategy in patients who demonstrate response and tolerability." [6] That language appears in the 2016 AACE/ACE obesity clinical practice guidelines and has been reinforced by post-SURMOUNT-4 clinical commentary.

Thinking about the evidence in terms of three clinical decision points helps frame the SURMOUNT program findings:

Decision 1: Is this patient a candidate for pharmacotherapy? SURMOUNT-1 and STEP-1 data support initiation in adults with BMI 30 or greater, or BMI <27 with a qualifying comorbidity.

Decision 2: Which agent? SURMOUNT-1 versus STEP-1 comparisons (not head-to-head trials) suggest tirzepatide 15 mg produces roughly 6 percentage points more mean weight loss than semaglutide 2.4 mg at similar timepoints. A head-to-head trial (SURMOUNT-5) completed enrollment in 2024; results are pending.

Decision 3: How long? SURMOUNT-4 provides the clearest available answer. Stopping after achieving goal weight leads to regain of the majority of that loss within 12 months. Patients and prescribers should plan for indefinite therapy unless a specific reason for discontinuation exists.

STEP-1: The Semaglutide Efficacy Benchmark

STEP-1 (N=1,961) randomized adults with obesity or overweight and no type 2 diabetes to subcutaneous semaglutide 2.4 mg once weekly or placebo for 68 weeks, alongside lifestyle counseling. Published in the New England Journal of Medicine in 2021, it reported a mean weight change of negative 14.9% in the semaglutide group versus negative 2.4% in the placebo group. [7]

Critically, 86.4% of semaglutide participants lost at least 5% of body weight, compared with 31.5% on placebo. One in three participants on the 2.4 mg dose lost more than 20% of body weight. The Wegovy FDA label (approved 2021, updated 2024) reflects these outcomes and carries the same BMI thresholds as the Zepbound label. [8]

STEP-1 also measured waist circumference, blood pressure, and cardiometabolic biomarkers. Reductions in all three were significant. That multi-marker improvement became the basis for the SELECT trial's cardiovascular hypothesis.

STEP-2: Semaglutide Efficacy in Type 2 Diabetes

STEP-2 (N=1,210), published in The Lancet in 2021, enrolled adults with type 2 diabetes and obesity. [9] Semaglutide 2.4 mg produced 9.6% mean weight loss versus 3.4% for placebo at 68 weeks. As with the SURMOUNT-1/SURMOUNT-2 comparison, the presence of type 2 diabetes attenuated the weight loss response by roughly 5 percentage points relative to the non-diabetic STEP-1 population.

HbA1c fell by 1.6 percentage points with semaglutide 2.4 mg versus 0.4 points with placebo. That glycemic effect occurs even though the approved Wegovy indication does not include a glycemic label claim, because the drug is Ozempic (a different formulation and dose) in the diabetes setting.

STEP-3: Adding Intensive Behavioral Therapy

STEP-3 (N=611) paired semaglutide 2.4 mg with intensive behavioral therapy (IBT), 30 counseling sessions across 68 weeks, and compared that combination with IBT plus placebo. Published in JAMA in 2021, the trial reported 16.0% mean weight loss with semaglutide plus IBT versus 5.7% with IBT alone. [10]

The incremental benefit of IBT over standard lifestyle counseling (as used in STEP-1) was modest, adding roughly 1 percentage point to weight loss in the semaglutide arm. That finding suggests the pharmacological effect of semaglutide dwarfs the behavioral component in terms of body-weight endpoints, even when behavioral intensity is high.

STEP-5: Two Years of Sustained Semaglutide Effect

Most obesity pharmacotherapy trials stop at 68 to 72 weeks. STEP-5 ran 104 weeks, providing the longest placebo-controlled dataset for semaglutide 2.4 mg. Published in Nature Medicine in 2022, it enrolled 304 adults with obesity and no type 2 diabetes. [11]

Mean weight loss at 104 weeks was 15.2% with semaglutide versus 2.6% with placebo. There was no clinically meaningful attenuation of effect between weeks 68 and 104. That plateau data is important: it argues against tachyphylaxis (loss of drug effect over time) and supports the SURMOUNT-4 interpretation that weight regain after stopping is not caused by fading drug efficacy but by cessation of the physiological mechanism the drug was providing.

SELECT Trial: Cardiovascular Outcomes With Semaglutide

The SELECT trial (N=17,604) deserves mention alongside the STEP and SURMOUNT programs because it reframed how semaglutide is classified medically. Published in the New England Journal of Medicine in 2023, SELECT enrolled adults with pre-existing cardiovascular disease and overweight or obesity, but no diabetes. [12]

Over a median follow-up of 33.3 months, semaglutide 2.4 mg reduced the composite of cardiovascular death, non-fatal myocardial infarction, and non-fatal stroke by 20% relative to placebo (hazard ratio 0.80; 95% CI 0.72 to 0.90; P<0.001). [12] That outcome was achieved in a non-diabetic population, ruling out glycemic improvement as the primary driver.

Mean weight loss in SELECT was 9.4% with semaglutide versus 0.9% with placebo, smaller than STEP-1 figures because the trial was powered for cardiovascular events rather than weight loss, and lifestyle counseling was not protocol-mandated.

As Dr. A. Michael Lincoff, the SELECT principal investigator, stated in the published paper: "The effects of semaglutide on cardiovascular outcomes were consistent across a broad range of patient subgroups, including those defined according to body-mass index, age, and sex." [12]

STEP-8: Semaglutide Versus Liraglutide Head-to-Head

One key gap in the STEP program was direct comparison with an older GLP-1 agent. STEP-8 (N=338) provided that data, randomizing participants to semaglutide 2.4 mg once weekly or liraglutide 3.0 mg daily for 68 weeks. Published in JAMA in 2022, it reported 15.8% mean weight loss with semaglutide versus 6.4% with liraglutide, a difference of 9.4 percentage points. [13]

Semaglutide also produced greater reductions in waist circumference and a lower rate of discontinuation due to gastrointestinal adverse events (3.0% vs. 12.6%). The data effectively ended the clinical debate about whether weekly semaglutide 2.4 mg offers a meaningful advantage over daily liraglutide 3.0 mg (Saxenda). It does, by roughly double the weight loss with fewer treatment stops.

Practical Dosing Timelines Across Both Programs

The titration schedules in both programs matter for patient counseling because gastrointestinal tolerability is time-dependent.

For tirzepatide, the approved Zepbound titration starts at 2.5 mg weekly for 4 weeks, then increases by 2.5 mg every 4 weeks toward 5 mg, 10 mg, or 15 mg maintenance. [3] Reaching 15 mg from initiation therefore takes a minimum of 20 weeks. SURMOUNT-4 participants had 36 weeks before randomization, meaning most had been at their maximum tolerated dose for 4 to 16 weeks before the withdrawal experiment began.

For semaglutide, the Wegovy titration starts at 0.25 mg weekly for 4 weeks, escalates through 0.5 mg and 1.0 mg and 1.7 mg, with the 2.4 mg maintenance dose reached at week 16 at the earliest. [8] STEP-1 participants were considered at maintenance dose from week 16 through week 68, meaning they had roughly 52 weeks at full dose.

Both titration timelines mean that clinicians evaluating early non-response should wait until the patient has been at maximum tolerated dose for at least 12 weeks before classifying the trial as inadequate.

Who Responds Best: Patient Characteristics Across Trials

Across SURMOUNT-1, SURMOUNT-2, STEP-1, and STEP-2, several patient-level predictors of greater weight loss appear consistently.

Patients without type 2 diabetes lose more weight than those with T2D, as described above. Patients with higher baseline BMI tend to lose larger absolute amounts but similar or slightly lower percentage amounts. Age does not appear to strongly predict response within adult populations in any of these trials.

Baseline HbA1c below 5.7% (normoglycemic) was associated with greater weight loss in pooled analyses of tirzepatide trials. Race and ethnicity data from SURMOUNT-1 showed non-Hispanic White and Hispanic participants lost somewhat more weight than Black participants at the same doses, though the absolute differences were modest and confidence intervals were wide. Eli Lilly has not published a pre-specified subgroup analysis on this endpoint with sufficient statistical power to draw firm conclusions.

Monitoring Parameters During Treatment

Neither the Zepbound nor the Wegovy FDA label specifies mandatory laboratory monitoring intervals beyond standard of care for the underlying conditions being treated. Clinically, the following are reasonable baselines informed by trial-program adverse event reporting:

Thyroid monitoring is relevant because both drug classes carry a warning about thyroid C-cell tumor risk (observed in rodents; human relevance not established). Patients with a personal or family history of medullary thyroid carcinoma or MEN2 are contraindicated on both agents. [3,8]

Gallbladder disease: SURMOUNT-1 reported cholelithiasis in 1.3% of the 15 mg group versus 0.4% of placebo, a difference driven by the well-documented association between rapid weight loss and gallstone formation. Baseline abdominal ultrasound is not required by label but may be appropriate in high-risk patients.

Pancreatitis: Acute pancreatitis occurred in 0.2% of tirzepatide and semaglutide arms across trials, numerically similar to placebo rates. Discontinue the drug if pancreatitis is confirmed.

Heart rate: Both drugs modestly increase resting heart rate by 2 to 4 beats per minute on average. The clinical significance in patients without arrhythmia history is unclear.