Switching to tirzepatide beats raising the dulaglutide dose in type 2 diabetes trial

In a randomized phase 4 trial, adults with type 2 diabetes who were not at their blood sugar goal while taking lower doses of dulaglutide did better when they switched to tirzepatide than when they stayed on dulaglutide at a higher dose ^[1]. The 40-week study, called SURPASS-SWITCH, reported larger reductions in hemoglobin A1c and body weight in the group that switched ^[1].

What the trial did

The trial enrolled 282 adults at 38 sites in 5 countries ^[1]. Participants had an HbA1c between 7.0% and 9.5%, a body mass index of at least 25, and had been on a stable dose of dulaglutide 0.75 mg or 1.5 mg for at least six months, along with zero to three oral diabetes medications for at least three months ^[1].

They were randomly assigned either to switch to tirzepatide, given at 15 mg or the maximum tolerated dose (139 people), or to escalate dulaglutide to 4.5 mg or the maximum tolerated dose (143 people) ^[1]. Tirzepatide is a once-weekly drug that acts on both the GIP and GLP-1 receptors and is approved to treat adults with type 2 diabetes or obesity ^[1].

The main measure was change in HbA1c at week 40. The key secondary measure was change in weight at week 40 ^[1].

The results

HbA1c fell by 1.44 percentage points with tirzepatide and by 0.67 points with the higher dulaglutide dose, an estimated difference of 0.77 points in favor of switching (95% CI, 0.98 to 0.56 points; P < 0.001) ^[1].

Weight fell by 10.5 kg with tirzepatide and by 3.6 kg with escalated dulaglutide, a difference of 6.9 kg (95% CI, 8.3 to 5.5 kg; P < 0.001) ^[1].

The trial was open-label, meaning participants and investigators knew which treatment was being given, and the authors list that as a limitation ^[1].

Side effects

Serious adverse events were reported by 10 participants (7.2%) in the tirzepatide group and 10 (7.0%) in the dulaglutide group ^[1]. The most common treatment-emergent adverse events in both groups were nausea and diarrhea ^[1]. The abstract does not list less common side effects or any breakdown by dose level.

The trial was funded by Eli Lilly and Company ^[1]. Funding sources are disclosed in trial reports so readers can weigh them; the published abstract does not say how the company was involved in the design, analysis or reporting of the study.

Why it matters for patients

Dulaglutide and tirzepatide are different drugs with different targets, so this is a question about switching products, not about taking a higher dose of the same one. For adults in the situation studied — on 0.75 mg or 1.5 mg of dulaglutide, with an A1c between 7.0% and 9.5% — the trial found that changing drugs produced about three times the A1c reduction and roughly three times the weight loss seen with a dose increase, over 40 weeks ^[1].

That difference in average results does not predict what any one person will experience. The trial tested one specific switch at one time point, and it did not compare switching against other options, such as adding another diabetes medicine or switching to a different GLP-1 drug. It also did not report heart, kidney or other long-term outcomes, and it followed participants for only 40 weeks ^[1].

Practical questions that come with a switch — whether insurance covers tirzepatide for a person already taking dulaglutide, what the out-of-pocket cost would be, and how a change in supply or pharmacy stock might affect timing — are not addressed in the trial report and have not been disclosed.

What happens next

The trial is registered as NCT05564039 ^[1]. No regulatory filing, label change, or longer-term follow-up tied to these results has been reported. It is also not yet known whether the results have changed how doctors counsel patients already taking dulaglutide at a lower dose.