SUSTAIN-7 Trial: A Plain-English Overview of What It Established

At a glance

| Field | Detail | |---|---| | Trial Name | SUSTAIN-7 | | Design | Open-label, randomized, phase 3b, parallel-group RCT | | N | 1,201 | | Intervention | Semaglutide 0.5 mg SC once weekly OR semaglutide 1.0 mg SC once weekly | | Comparator | Dulaglutide 0.75 mg SC once weekly OR dulaglutide 1.5 mg SC once weekly | | Background Therapy | Metformin (stable dose) | | Duration | 40 weeks | | Primary Endpoints | Change from baseline in A1C and body weight at week 40 | | Key Results | Semaglutide superior on both endpoints at both dose comparisons | | Journal | Lancet Diabetes & Endocrinology, 2018 | | Primary Source | PubMed 29395633 |

Why a Head-to-Head Trial Was Needed

By the mid-2010s, GLP-1 receptor agonists had multiplied quickly. Exenatide, liraglutide, dulaglutide, and semaglutide each carried placebo-controlled trial packages, but clinicians trying to choose between them had almost no direct comparative data. Indirect cross-trial comparisons are unreliable because populations, background therapies, and titration schedules differ in ways that inflate or suppress apparent differences. Semaglutide's FDA approval in 2017 was built primarily on the SUSTAIN 1-5 program against placebo, sitagliptin, and insulin, so the question of how it performed against another injectable GLP-1 agonist remained genuinely open before SUSTAIN-7 was published in Lancet Diabetes & Endocrinology in 2018.

Dulaglutide was the natural comparator. It had already demonstrated cardiovascular safety in REWIND (published later, but the compound was widely used), it was once-weekly like semaglutide, and it occupied the same slot in ADA Standards of Care guidance on GLP-1 selection. A direct trial comparing the two at clinically used doses gave prescribers something they could actually apply.

Who Was Enrolled

Investigators recruited adults aged 18 or older with type 2 diabetes who had an A1C between 7.5% and 10.5% and had been on a stable metformin dose (at least 1 to 500 mg/day or maximum tolerated) for 90 days or more before screening. The mean baseline A1C was approximately 8.2%, mean body weight was around 95 kg, and mean duration of diabetes was roughly 8 years. These are fairly typical community patients with moderately uncontrolled diabetes on oral monotherapy, not highly selected academic-center populations.

Exclusion criteria included prior use of any GLP-1 receptor agonist, use of insulin within 90 days, severe renal impairment (eGFR <30 mL/min/1.73 m²), and a history of pancreatitis. The renal cutoff matters clinically because both drugs are used in patients with moderate chronic kidney disease, and excluding the most impaired patients means the results apply cleanly only down to an eGFR around 30.

Participants were randomized 1:1:1:1 across four arms. The two semaglutide arms and two dulaglutide arms were powered to detect superiority within each dose-matched pair separately.

Intervention and Titration Details

Semaglutide was started at 0.25 mg once weekly for four weeks, escalated to 0.5 mg at week 4, and (in the 1.0 mg arm) further escalated to 1.0 mg at week 8. Dulaglutide 0.75 mg was given at the fixed dose throughout. Dulaglutide 1.5 mg was also given at the fixed dose throughout; dulaglutide does not require an escalation scheme in the same way because its gastrointestinal tolerability profile differs from semaglutide's.

This asymmetry in titration is worth noting because critics have pointed out that semaglutide's dose-escalation period means patients in the semaglutide arms spent the first eight weeks at sub-therapeutic doses while dulaglutide patients were at full dose from the start. The 40-week endpoint still favors semaglutide, but the titration imbalance does mean that early tolerability comparisons between arms are not straightforward. The primary SUSTAIN-7 publication acknowledged this design feature explicitly.

The trial was open-label. Both drugs are injected subcutaneously once weekly and have a similar pen-device form, so full blinding would have been logistically possible in principle. The open-label design introduces the risk of differential reporting of subjective outcomes (nausea, adherence) and differential dropout, though the authors used a confirmatory estimand approach to handle missing data.

What Was Measured

The co-primary endpoints were change in A1C from baseline to week 40 and change in body weight from baseline to week 40. Using two co-primary endpoints required a hierarchical testing procedure to control the family-wise error rate. A1C was tested first; if superior, weight was then formally tested. This is conservative and appropriate, and both tests achieved significance in both dose comparisons.

Secondary endpoints included the proportion of patients reaching A1C <7.0%, A1C ≤6.5%, the proportion losing at least 5% of body weight, fasting plasma glucose, seven-point self-measured plasma glucose profiles, blood pressure, lipids, and patient-reported outcomes using the Diabetes Treatment Satisfaction Questionnaire (DTSQ). Safety endpoints covered hypoglycemia (using American Diabetes Association definitions), adverse events, serious adverse events, and discontinuations due to adverse events.

Results in Detail

The results below summarize the outcomes published in Lancet Diabetes & Endocrinology at week 40.

Glycemic Outcomes

| Comparison | Sema A1C Change | Dula A1C Change | ETD (95% CI) | p-value | |---|---|---|---|---| | 0.5 mg vs 0.75 mg | -1.5% | -1.1% | -0.40% (-0.55 to -0.25) | <0.0001 | | 1.0 mg vs 1.5 mg | -1.8% | -1.4% | -0.41% (-0.57 to -0.25) | <0.0001 |

ETD = estimated treatment difference. Both semaglutide doses produced statistically and clinically meaningful additional A1C reductions. An ETD of roughly 0.4 percentage points exceeds what most clinicians regard as a minimum clinically important difference for A1C.

Proportions reaching A1C <7.0% were 67% for semaglutide 0.5 mg versus 52% for dulaglutide 0.75 mg, and 79% for semaglutide 1.0 mg versus 67% for dulaglutide 1.5 mg. These responder rates matter at the individual patient level because they translate the mean difference into probability-of-goal language.

Weight Outcomes

| Comparison | Sema Weight Change | Dula Weight Change | ETD (95% CI) | p-value | |---|---|---|---|---| | 0.5 mg vs 0.75 mg | -4.6 kg | -2.3 kg | -2.26 kg (-2.94 to -1.58) | <0.0001 | | 1.0 mg vs 1.5 mg | -6.5 kg | -3.0 kg | -3.55 kg (-4.32 to -2.78) | <0.0001 |

The weight difference at the higher-dose comparison is particularly striking. A mean difference of more than 3.5 kg at 40 weeks, on top of baseline weights around 95 kg, represents a clinically meaningful separation. Roughly 49% of semaglutide 1.0 mg patients lost at least 5% of body weight, compared with 26% in the dulaglutide 1.5 mg arm.

Cardiovascular Risk Markers and Blood Pressure

Systolic blood pressure fell more in the semaglutide arms. The difference was approximately 3 mmHg at the higher-dose comparison, consistent with the weight-loss advantage. Both drugs produced broadly similar changes in LDL cholesterol and triglycerides.

Safety and Tolerability

Gastrointestinal adverse events (nausea, diarrhea, vomiting) were more frequent with semaglutide. Nausea occurred in roughly 22-24% of semaglutide patients versus 14-18% of dulaglutide patients. Discontinuation due to adverse events was numerically higher with semaglutide (5-7%) than dulaglutide (3-4%), though these differences did not reach formal significance at standard thresholds.

Hypoglycemia rates were low across all arms, consistent with the metformin background and the mechanism of GLP-1 receptor agonists. No new safety signals emerged. Injection-site reactions, pulse rate, and lipase elevations were reported in line with the established profiles of both agents documented in their respective FDA prescribing information for semaglutide and FDA prescribing information for dulaglutide.

Limitations Worth Knowing

The open-label design is the most commonly cited methodological limitation. Because both patients and investigators knew the treatment assignment, the potential for differential reporting of nausea, injection preferences, and satisfaction scores is real. A double-dummy blinded design was feasible and would have been stronger.

The 40-week duration is relatively short for a chronic disease trial. Weight loss with GLP-1 agonists often continues beyond 40 weeks, and the trajectory may diverge further or narrow at longer follow-up. The REWIND trial for dulaglutide, which ran for a median of 5.4 years, provides important long-term cardiovascular data on dulaglutide but was not a direct glycemic or weight comparison against semaglutide.

The trial enrolled only patients on metformin background, which limits generalizability to those on other oral agents, those with renal impairment, or insulin-naive patients who need a more complex regimen. The cardiovascular outcomes superiority shown in SUSTAIN-6 for semaglutide and in REWIND for dulaglutide were not directly compared here; SUSTAIN-7 was not powered or designed for cardiovascular endpoints.

Sponsor funding (Novo Nordisk manufactures semaglutide) is disclosed and standard for industry-sponsored phase 3b trials. The independent statistical analysis plan and the use of a confirmatory estimand approach strengthen confidence in the analysis, but readers should note that the dose-matching in SUSTAIN-7 is one of several legitimate ways to pair the two drugs and a different dose-matching choice could alter the magnitude of the difference.

What It Means for Clinical Practice

SUSTAIN-7 gave clinicians solid comparative data to inform GLP-1 selection when two goals are present: improving A1C and reducing body weight. The 2024 ADA Standards of Medical Care in Diabetes continue to recommend GLP-1 receptor agonists with proven cardiovascular or renal benefit for patients with established cardiovascular disease or high cardiovascular risk, and semaglutide's profile across SUSTAIN-6 and SUSTAIN-7 supports its positioning in patients where weight reduction is a priority alongside glycemic control.

For patients who prioritize tolerability over maximal weight loss, dulaglutide's lower nausea rates may be a reasonable reason to choose it, and its cardiovascular data from REWIND are independently reassuring. The head-to-head superiority in SUSTAIN-7 does not mean dulaglutide is an inferior drug in absolute terms; it means semaglutide produces larger mean changes on these endpoints in this population at these doses. Individual patient factors, including gastrointestinal history, cost, and cardiovascular risk category, remain important. A 2021 systematic review and network meta-analysis broadly corroborated the SUSTAIN-7 finding that semaglutide produces among the largest A1C and weight reductions of any GLP-1 receptor agonist in the class.

Frequently asked questions

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References

1. Pratley R, Aroda VR, Lingvay I, et al. Semaglutide versus dulaglutide once weekly in patients with type 2 diabetes (SUSTAIN 7): a randomised, open-label, phase 3b trial. Lancet Diabetes Endocrinol. 2018;6(4):275-286. https://pubmed.ncbi.nlm.nih.gov/29395633/

2. Marso SP, Bain SC, Consoli A, et al. Semaglutide and cardiovascular outcomes in patients with type 2 diabetes (SUSTAIN-6). N Engl J Med. 2016;375(19):1834-1844. https://pubmed.ncbi.nlm.nih.gov/27633186/

3. Gerstein HC, Colhoun HM, Dagenais GR, et al. Dulaglutide and cardiovascular outcomes in type 2 diabetes (REWIND). Lancet. 2019;394(10193):121-130. https://pubmed.ncbi.nlm.nih.gov/31189511/

4. Tsapas A, Avgerinos I, Karagiannis T, et al. Comparative effectiveness of glucose-lowering drugs for type 2 diabetes: a systematic review and network meta-analysis. Ann Intern Med. 2020;173(4):278-286. https://pubmed.ncbi.nlm.nih.gov/33454002/

5. American Diabetes Association Professional Practice Committee. Standards of Medical Care in Diabetes 2024, Section 9: Pharmacologic Approaches to Glycemic Treatment. Diabetes Care. 2024;47(Suppl 1):S158-S178. https://diabetesjournals.org/care/article/47/Supplement_1/S158/153954/9-Pharmacologic-Approaches-to-Glycemic-Treatment

6. Ozempic (semaglutide) injection prescribing information. Novo Nordisk. FDA label, 2017. https://www.accessdata.fda.gov/drugsatfda_docs/label/2017/209637lbl.pdf

7. Trulicity (dulaglutide) injection prescribing information. Eli Lilly. FDA label, 2014. https://www.accessdata.fda.gov/drugsatfda_docs/label/2014/125469lbl.pdf