SUSTAIN-7 Results in Detail: Numbers, Subgroups, and Time Course

At a glance

Parameter	Detail
N	1,201 adults with type 2 diabetes
Intervention	Semaglutide 0.5 mg or 1.0 mg once weekly
Comparator	Dulaglutide 0.75 mg or 1.5 mg once weekly
Duration	40 weeks
Primary endpoint	Change from baseline in HbA1c
Key confirmatory endpoint	Change from baseline in body weight
Key result	Semaglutide superior to dulaglutide at both dose levels for A1C and weight

Trial Design and What the Abstract Leaves Out

SUSTAIN-7 was a phase 3b, open-label, active-comparator trial conducted across 194 sites in 16 countries. Patients had type 2 diabetes inadequately controlled on metformin monotherapy (mean baseline A1C approximately 8.2%). The trial randomized participants 1:1:1:1 to four arms: semaglutide 0.5 mg, semaglutide 1.0 mg, dulaglutide 0.75 mg, or dulaglutide 1.5 mg.

A detail worth noting: the dose pairings were chosen to match "low vs low" and "high vs high" as used in clinical practice, not milligram-for-milligram equivalence. Semaglutide 0.5 mg and dulaglutide 0.75 mg are each the recommended maintenance starting dose for their respective agents. Semaglutide 1.0 mg and dulaglutide 1.5 mg represent the maximum approved weekly doses at the time of the trial (dulaglutide has since gained approval for 3.0 mg and 4.5 mg doses).

The open-label design is the most common criticism. Blinding was not performed because the devices and titration schedules differ between agents. The investigators addressed potential bias by using a central laboratory for A1C measurements and by pre-specifying the statistical hierarchy.

Primary Endpoint: HbA1c Change at Week 40

The table below presents the estimated treatment differences from a mixed model for repeated measures (MMRM) analysis, which was the pre-specified primary analysis method.

HbA1c Results by Dose Comparison

The 0.40 percentage point advantage of semaglutide 1.0 mg over dulaglutide 1.5 mg represents clinically relevant separation. For context, most FDA approvals for glucose-lowering agents are granted on placebo-adjusted A1C reductions of 0.3 to 0.5 percentage points.

A1C Target Achievement

The proportion of patients reaching standard glycemic targets was also significantly higher with semaglutide at both dose levels:

The number needed to treat (NNT) to get one additional patient to A1C <7.0% with semaglutide 1.0 mg vs dulaglutide 1.5 mg was approximately 8. That is a practical number for clinical decision-making.

Confirmatory Secondary Endpoint: Body Weight

Weight loss results were the confirmatory secondary endpoint, tested only after the A1C hierarchy succeeded.

The 4.6 kg difference between the higher-dose arms is striking. In percentage terms, semaglutide 1.0 mg produced roughly 6.5% body weight reduction vs approximately 3.0% with dulaglutide 1.5 mg. This weight gap between agents has since been confirmed in real-world comparative effectiveness analyses.

Weight Loss Response Distribution

The proportion achieving clinically meaningful weight thresholds:

More than a quarter of patients on semaglutide 1.0 mg lost at least 10% of their body weight, a threshold associated with improvements in cardiovascular risk markers and metabolic outcomes in T2D.

Time-Course Pattern: When Separation Emerges

The SUSTAIN-7 publication includes time-course data at weeks 4, 8, 16, 24, 32, and 40. Several patterns stand out.

For A1C, both agents showed rapid reductions through week 16. After week 16, the dulaglutide arms plateaued while semaglutide continued to drive A1C lower through week 28. By week 40, the curves were stable but separated. The separation between semaglutide 1.0 mg and dulaglutide 1.5 mg was apparent as early as week 8 and widened consistently through week 24.

For body weight, the pattern differed. Dulaglutide arms showed weight loss mostly in the first 16 weeks, with minimal additional loss afterward. Semaglutide arms continued losing weight through week 40 without a clear plateau. This ongoing trajectory is consistent with findings from the STEP trials, where higher-dose semaglutide (2.4 mg) showed continued weight loss out to 68 weeks.

The clinical implication: patients who switch from dulaglutide to semaglutide at the same GLP-1 class level should expect additional weight loss that accrues over months, not days.

Subgroup Analyses

Pre-specified subgroup analyses for the primary endpoint examined consistency across age (<65 vs ≥65 years), sex, baseline A1C (<8.5% vs ≥8.5%), baseline BMI (<30 vs ≥30 kg/m²), and duration of diabetes (<5 vs ≥5 years).

Across all subgroups, semaglutide maintained its A1C advantage. No significant treatment-by-subgroup interactions were detected. Two observations deserve attention:

Higher baseline A1C. Patients with baseline A1C ≥8.5% had larger absolute reductions in both arms, but the between-group difference favoring semaglutide was consistent regardless of starting glycemia.

BMI ≥30 kg/m². The weight loss advantage of semaglutide was numerically larger in the higher BMI subgroup. This aligns with the pharmacologic principle that GLP-1 receptor agonists with stronger appetite suppression effects produce greater absolute weight reduction when there is more adipose tissue to lose.

Safety and Tolerability: Gastrointestinal Signal

GI adverse events were the most common treatment-emergent side effects in all four arms. Nausea rates were higher with semaglutide (21-22%) than with dulaglutide (13-18%), though discontinuation rates due to GI events were low and comparable across arms (2-4%).

This nausea difference matters for clinical conversations. When counseling patients about switching from dulaglutide to semaglutide, or when choosing between agents initially, the greater efficacy of semaglutide comes with a modestly higher likelihood of transient nausea during the titration period. Most nausea resolved by weeks 8 to 12.

Serious adverse event rates were similar (6-8% across all arms). No new safety signals emerged relative to the individual agents' prescribing information.

Limitations the Authors Acknowledged

The published trial report explicitly raised these concerns:

1. Open-label design. Subjective outcomes (patient-reported nausea, satisfaction scores) could be influenced by knowledge of treatment assignment. Objective measures like A1C and body weight are less susceptible, but the potential for behavioral changes (diet, exercise) driven by treatment awareness cannot be excluded.

2. 40-week duration. Longer trials would be needed to confirm durability of the A1C and weight differences. The SUSTAIN program includes a 2-year extension (SUSTAIN-6) for cardiovascular outcomes, but the head-to-head comparison with dulaglutide was not extended.

3. Dose asymmetry. Dulaglutide has since been approved at higher doses (3.0 mg and 4.5 mg), which were not available at the time of SUSTAIN-7. A comparison of semaglutide 1.0 mg vs dulaglutide 4.5 mg would provide a more complete picture of the agents' dose-response profiles.

4. Metformin-only background. Patients were on metformin alone, which does not reflect the multi-drug regimens common in clinical practice. The treatment difference might narrow or widen depending on background therapy.

Putting SUSTAIN-7 in Context

SUSTAIN-7 was the first adequately powered, randomized head-to-head trial between two once-weekly GLP-1 receptor agonists. Before this study, clinicians choosing between semaglutide and dulaglutide relied on indirect comparisons across separate placebo-controlled trials, which carry the well-known limitations of cross-trial comparison.

The American Diabetes Association Standards of Care now list GLP-1 receptor agonists with proven cardiovascular benefit as preferred agents in T2D with established cardiovascular disease. Both semaglutide and dulaglutide have cardiovascular outcomes data (SUSTAIN-6 and REWIND, respectively), but SUSTAIN-7's glycemic and weight results have influenced formulary tiering and prior authorization criteria at many insurance plans.

For clinicians, the practical takeaway from the numbers is clear: when A1C reduction and weight loss are both priorities, semaglutide provides a measurable advantage over dulaglutide at approved doses. The gap is largest for weight (roughly double the percentage weight loss at the high-dose pairing) and clinically significant but smaller for A1C (0.40 percentage points).

Frequently asked questions

›What was the primary endpoint of SUSTAIN-7?

The primary endpoint was change from baseline in HbA1c at week 40. Semaglutide was superior to dulaglutide at both dose pairings, with estimated treatment differences of −0.30% (low doses) and −0.40% (high doses).

›How much more weight did patients lose on semaglutide vs dulaglutide?

At the higher dose pairing, semaglutide 1.0 mg produced 6.5 kg of weight loss compared to 3.0 kg with dulaglutide 1.5 mg, a difference of 4.6 kg (approximately 3.5 additional percentage points of body weight).

›Was SUSTAIN-7 blinded?

No. SUSTAIN-7 was an open-label trial because semaglutide and dulaglutide use different injection devices and titration schedules. The primary endpoint (A1C) was measured at a central laboratory to reduce measurement bias.

›What doses were compared in SUSTAIN-7?

The trial used four arms: semaglutide 0.5 mg vs dulaglutide 0.75 mg (low-dose comparison) and semaglutide 1.0 mg vs dulaglutide 1.5 mg (high-dose comparison). These were the maximum approved doses at the time. Dulaglutide 3.0 mg and 4.5 mg had not yet been approved.

›How quickly did A1C differences appear between semaglutide and dulaglutide?

Separation between semaglutide 1.0 mg and dulaglutide 1.5 mg was visible by week 8 and widened through week 24, after which the curves remained stable through week 40.

›Were GI side effects worse with semaglutide?

Nausea rates were modestly higher with semaglutide (21-22% vs 13-18% with dulaglutide), but discontinuation due to GI events was low across all arms (2-4%). Most nausea resolved within the first 8 to 12 weeks.

›Did subgroup analyses show consistent results?

Yes. Pre-specified subgroup analyses by age, sex, baseline A1C, BMI, and diabetes duration showed consistent superiority for semaglutide. No significant treatment-by-subgroup interactions were detected.

›How does SUSTAIN-7 influence prescribing decisions today?

SUSTAIN-7 provides direct comparison evidence showing semaglutide outperforms dulaglutide on glycemic control and weight loss. This has influenced formulary tiering, prior authorization criteria, and clinical guideline discussions about preferred GLP-1 agents when both outcomes are priorities.

›What is the number needed to treat for semaglutide vs dulaglutide?

For the outcome of reaching A1C <7.0%, the NNT with semaglutide 1.0 mg vs dulaglutide 1.5 mg was approximately 8. This means for every 8 patients switched from dulaglutide to semaglutide, one additional patient would reach the glycemic target.

›Does SUSTAIN-7 address cardiovascular outcomes?

No. SUSTAIN-7 was a 40-week glycemic and weight trial without cardiovascular event adjudication. Cardiovascular outcomes for semaglutide and dulaglutide come from separate trials: SUSTAIN-6 and REWIND, respectively.

References

1. Pratley RE, 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. PubMed
2. Ozempic (semaglutide) prescribing information. Novo Nordisk. FDA Label
3. Trulicity (dulaglutide) prescribing information. Eli Lilly. FDA Label
4. Blonde L, Belousova L, Fainberg U, et al. Comparative effectiveness of semaglutide and dulaglutide in clinical practice. Diabetes Obes Metab. 2021;23(12):2783-2793. PubMed
5. American Diabetes Association Professional Practice Committee. Standards of Care in Diabetes, 2023. Diabetes Care. 2023;46(Suppl 1). PubMed
6. Wilding JPH, Batterham RL, Calanna S, et al. Once-weekly semaglutide in adults with overweight or obesity (STEP 1). N Engl J Med. 2021;384(11):989-1002. PubMed