Managing type 2 diabetes often means adjusting and layering treatments over time as the condition progresses. Insulin has long been a mainstay, but researchers have grown increasingly interested in whether combining insulin with a different class of compound, specifically a glucagon-like peptide-1 (GLP-1) receptor agonist, can push blood sugar control further without raising the risk of dangerous low-glucose episodes.
A published phase 3b trial called ONWARDS 8 set out to answer that question in a structured way. The trial enrolled adults whose blood sugar was not fully controlled on daily basal insulin alone, switched them to a once-weekly insulin formulation for half a year, and then added a once-weekly GLP-1 peptide called semaglutide for the second half. The researchers tracked changes in a standard blood sugar marker, body weight, and safety outcomes across the full year.
Trial design at a glance
ONWARDS 8 was a single-arm, open-label, treat-to-target study, meaning every participant received the same sequence of treatments and both participants and researchers knew what was being given. There was no placebo group. The trial ran for 52 weeks in total, split into two back-to-back 26-week periods.
During the first period, participants switched from their existing daily basal insulin to a once-weekly insulin. This run-in phase standardized their starting point before the second medication was introduced. At week 26, those whose glycated hemoglobin (HbA1c) remained above 7.0 percent but no higher than 10.5 percent moved into the intensification phase, where the GLP-1 peptide was added at doses up to 1.0 mg per week.
A total of 148 adults with type 2 diabetes were enrolled. Of those, 94 met the criteria to begin the GLP-1 peptide addition. Participants were eligible only if they were not already using a GLP-1 receptor agonist, which kept the measured effect attributable to the new combination.
What GLP-1 peptides do in the body
GLP-1 is a hormone released naturally from the gut after eating. It signals the pancreas to release insulin when glucose is present, slows the emptying of the stomach, and acts on areas of the brain involved in appetite signaling. Synthetic peptides that mimic GLP-1 and resist rapid breakdown have been studied extensively for their effects on blood glucose and body weight.
Semaglutide belongs to this class. Its chemical structure has been modified so that it binds to albumin in the blood, extending its half-life long enough to allow once-weekly dosing. The trial record describes it as a GLP-1 receptor agonist, which means it activates the same receptor that natural GLP-1 targets, amplifying the body's own glucose-lowering and satiety-related pathways.
Because GLP-1 peptides lower glucose primarily by a glucose-dependent mechanism, meaning they boost insulin release mainly when blood sugar is elevated, they carry a lower inherent risk of hypoglycemia compared with insulin acting alone. That characteristic made the combination worth studying: adding a GLP-1 peptide might improve control while the insulin dose could potentially be reduced.
Key measurements and results
The primary endpoint was the change in HbA1c from week 26, the point when semaglutide was introduced, to week 52, the end of the trial. HbA1c reflects average blood glucose over roughly the prior three months, so it captures sustained trends rather than single-day fluctuations.
From a mean observed HbA1c of 7.88 percent at the start of the intensification phase, the estimated mean fell to 6.66 percent by week 52. That represents an estimated reduction of 1.23 percentage points, and the result was statistically significant with a p-value below 0.0001, meaning the probability of seeing a change this large by chance alone is extremely low.
The trial also measured a 7-point self-monitored blood glucose profile, which captures glucose at multiple times of day across different meal contexts. That measure dropped by an estimated 1.72 mmol/L. Postprandial glucose, the rise in blood sugar specifically after meals, fell by 1.31 mmol/L. Body weight decreased by a mean of 3.85 kilograms. All three of those secondary outcomes also reached statistical significance.
Insulin dose changes during the trial
One notable finding was what happened to the weekly insulin dose once the GLP-1 peptide was introduced. Per the trial protocol, 69.1 percent of participants had their insulin dose reduced by 20 percent at week 26 when semaglutide was added. This pre-planned reduction was a safety precaution to lower the risk of hypoglycemia from having two glucose-lowering agents active simultaneously.
Despite that starting reduction, the mean weekly insulin dose continued to decrease over the intensification period. By week 52, the relative decrease in mean weekly dose from week 25 to week 52 was 24 percent. The researchers interpreted this as consistent with the GLP-1 peptide carrying meaningful glucose-lowering activity that allowed less insulin to be needed to hit the same target range.
Safety profile and hypoglycemia rates
For any study combining insulin with another glucose-lowering compound, the safety signal researchers pay closest attention to is hypoglycemia, the state where blood glucose drops low enough to cause symptoms or require intervention. The trial tracked a combined category of clinically significant or severe hypoglycemia from week 26 through week 57, the full end-of-trial window.
The observed rate was 0.24 episodes per person-year of exposure. The trial abstract characterizes this as a low rate, particularly given that participants were using insulin and therefore had baseline exposure to hypoglycemia risk. The authors concluded that intensification with the GLP-1 peptide was feasible and that the safety profile over the observation window appeared manageable.
It is worth noting that this was a single-arm trial without a comparison group, so the rate cannot be directly benchmarked against a parallel control within the same study. The result should be read as a descriptive finding within this specific population and protocol rather than a definitive comparative statement.
Context for the research peptide field
The ONWARDS 8 findings add to a growing body of published trial data on GLP-1 receptor agonist peptides used in combination regimens for metabolic conditions. The ability to reduce insulin requirements while improving HbA1c is a pattern that has appeared in earlier trials of this class, and this phase 3b study extends that observation into a structured treat-to-target framework using a once-weekly insulin.
For researchers and science-curious readers tracking peptide pharmacology, the trial illustrates how the glucose-dependent mechanism of GLP-1 peptides interacts with exogenous insulin. The combination does not simply add two independent effects. Instead, the GLP-1 peptide appears to allow the insulin component to be dialed back, suggesting a complementary rather than purely additive relationship at the receptor level.
The literature continues to explore how different peptide combinations and dosing sequences affect metabolic endpoints. Early data from this and related trials point at combination approaches as a productive area for further investigation, though the field is still working out optimal sequencing, dose titration strategies, and long-term safety profiles across diverse patient populations.
