Tirzepatide Added to Insulin Dramatically Improved Blood Sugar Control in Chinese Type 2 Diabetes Patients | Research

The takeaway

In the SURPASS-CN-INS trial, adding weekly tirzepatide to daily basal insulin reduced HbA1c by up to 2.39% versus 0.91% with placebo over 40 weeks in Chinese patients with uncontrolled type 2 diabetes.

-1.48%
HbA1c reduction difference between tirzepatide 10mg and placebo at week 40 — a highly significant clinical improvement (p<0.0001)

What the researchers found

Tirzepatide added to basal insulin produced significant HbA1c reductions at week 40:

- Tirzepatide 10mg: -2.39% (SE 0.13) vs placebo -0.91% (SE 0.12); difference -1.48% (97.5% CI -1.87 to -1.08; p<0.0001)

- Tirzepatide 15mg: -2.37% (SE 0.13) vs placebo -0.91%; difference -1.45% (97.5% CI -1.85 to -1.06; p<0.0001)

- Tirzepatide 5mg also showed improvements (specific numbers not primary endpoint)

The most common adverse events were gastrointestinal: diarrhea (26-37% vs 8%), decreased appetite (25-32% vs 0%), nausea (5-11% vs 3%), and vomiting (6-9% vs 0%), predominantly mild or moderate.

Why it matters

China has the world's largest diabetes population (~140 million), and many patients remain inadequately controlled on basal insulin. This trial demonstrates that tirzepatide can be safely and effectively added to existing insulin therapy, providing a much-needed intensification option. The magnitude of HbA1c reduction (~1.5% beyond placebo) is clinically very significant and could prevent serious diabetic complications.

How the study worked

SURPASS-CN-INS was a 40-week, double-blind, multicentre, randomized, placebo-controlled phase 3 trial across 26 hospitals in China. 257 patients with uncontrolled type 2 diabetes on insulin glargine (± metformin ± SGLT2 inhibitor) were randomized 1:1:1:1 to weekly subcutaneous tirzepatide 5mg, 10mg, 15mg, or placebo. Randomization was stratified by baseline HbA1c and SGLT2 inhibitor use. The primary endpoint was HbA1c change from baseline to week 40.

What this study cannot tell us

The sample size (257 patients) is relatively modest for a phase 3 trial. The 40-week duration may not capture long-term safety signals or durability of effect. The trial was conducted exclusively in Chinese patients, so results may not be fully generalizable to other populations. The study was funded by Eli Lilly, the manufacturer. GI side effects, while mostly mild, were substantially more frequent with tirzepatide than placebo.

How to read the evidence

This is a phase 3, double-blind, randomized, placebo-controlled trial published in The Lancet Diabetes & Endocrinology — the highest level of clinical evidence. The design is rigorous with proper randomization, blinding, and stratification.

When this study was published

Published in 2025, this is current phase 3 data from the SURPASS-CN-INS trial, relevant to ongoing regulatory review of tirzepatide in China.

The bigger picture

This trial is part of the global SURPASS program for tirzepatide, providing specific evidence for the Chinese population — a regulatory requirement for drug approval in China. Combined with SURPASS-1 through SURPASS-5 and the SURMOUNT obesity trials, this fills an important data gap for the world's largest diabetes market. The results also reinforce that tirzepatide's benefits extend to patients already on insulin, not just those on oral medications.

Questions still open

Can tirzepatide eventually replace basal insulin entirely in some patients with type 2 diabetes, rather than being used as add-on therapy?
How do the HbA1c reductions in this Chinese cohort compare to the global SURPASS-5 trial that tested tirzepatide plus insulin?
Will the GI side effect profile be acceptable for long-term use in routine clinical practice in China?

Common questions

Why would someone need tirzepatide if they're already on insulin?

Many people with type 2 diabetes don't achieve their blood sugar targets on insulin alone, even at high doses. Adding tirzepatide — which works through completely different mechanisms (GIP and GLP-1 receptors) — can provide additional glucose control, reduce appetite, and potentially allow for lower insulin doses. This trial showed the combination reduced HbA1c by about 1.5% more than insulin alone.

Why was this trial specifically done in China?

China has the world's largest diabetes population, and regulatory agencies typically require clinical trial data from local populations before approving a new drug. This is because genetic, dietary, and metabolic factors can influence how a drug works in different populations. The SURPASS-CN-INS trial provides the evidence needed for tirzepatide approval in China for this specific indication.

Read the original research

Efficacy and safety of tirzepatide added to basal insulin in patients with type 2 diabetes in China (SURPASS-CN-INS): a double-blind, multicentre, randomised, placebo-controlled, phase 3 trial.

The lancet. Diabetes & endocrinology, 13(12), 1015-1029

View on PubMed ↗Publisher’s paper ↗

Citation

Guo, Lixin; Dong, Xiaolin; Ma, Jianhua; Liu, Ming; Lu, Yibing; Wang, Hongman; Li, Qingju; Li, Ling; Deng, Yuying; Xu, Jiawei. (2025). Efficacy and safety of tirzepatide added to basal insulin in patients with type 2 diabetes in China (SURPASS-CN-INS): a double-blind, multicentre, randomised, placebo-controlled, phase 3 trial.. The lancet. Diabetes & endocrinology, 13(12), 1015-1029. https://doi.org/10.1016/S2213-8587(25)00248-7