Diabetes CareType 1 DiabetesRCTJanuary 1, 2026

Tirzepatide in Adults With Type 1 Diabetes: A Phase 2 Randomized Placebo-Controlled Clinical Trial.

Snaith JR, Frampton R, Samocha-Bonet D, Greenfield JR

Key Finding

In adults with type 1 diabetes and obesity, tirzepatide caused an average 10.3 kg (22.7 lb) weight loss over 12 weeks compared to just 0.7 kg in the placebo group - that's nearly 9% of their body weight lost.

What This Study Found

This small but important study tested tirzepatide - think of it as a dual-action hormone mimicker that targets both GIP and GLP-1 receptors - in 24 adults with type 1 diabetes and obesity (BMI over 30). Unlike type 2 diabetes where these drugs are well-established, this was uncharted territory for type 1 diabetes patients. The results were striking: after 12 weeks on tirzepatide, people lost an average of 22.7 pounds compared to just 1.5 pounds with placebo - imagine the difference between losing a medium-sized dog versus a bag of flour. Even more impressive, every single person on tirzepatide (100%) lost at least 5% of their body weight, and nearly half (45%) lost 10% or more, while the placebo group saw almost no meaningful weight loss (only 9% lost 5% or more, and nobody hit 10%). As a bonus, their blood sugar control improved (HbA1c dropped by 0.4%) and they needed 35% less insulin daily - like their bodies became more efficient at using the insulin they injected.

Statistics Decoded

The p-value of <0.0001 for weight loss means this result definitely wasn't just luck - like flipping heads 50 times in a row. The 95% confidence interval of -12.0 to -5.5 kg for the treatment difference means we're pretty sure the real weight loss advantage is somewhere between 12 and 27 pounds. The 8.8% weight loss represents clinically meaningful weight reduction. For insulin reduction, the 35% decrease (p=0.0002) means people could cut their daily insulin by about one-third while maintaining better blood sugar control - this probably wasn't coincidence either. The HbA1c improvement of -0.4% with p=0.05 is right at the edge of statistical significance - like flipping heads 20 times in a row, so we're reasonably confident but it's borderline.

Why This Matters

This opens a potential new treatment avenue for the estimated 40% of type 1 diabetics who struggle with obesity - a group that previously had limited safe weight loss options since most diabetes medications are designed for type 2. The dual benefit of weight loss plus reduced insulin needs could significantly lower cardiovascular risks in this vulnerable population.

Original Abstract

Overweight and obesity are prevalent in type 1 diabetes and contribute to cardiovascular risk. Tirzepatide, a gastric inhibitory polypeptide and glucagon-like peptide 1 receptor coagonist, has not been studied in type 1 diabetes. We conducted a 12-week, phase 2, double-blind, placebo-controlled trial in adults with type 1 diabetes and BMI >30 kg/m2. Participants were randomized to once-weekly subcutaneous tirzepatide (2.5 mg for 4 weeks, 5.0 mg for 8 weeks) or placebo. The primary end point was change in body weight at 12 weeks. Twenty-two of 24 adults with type 1 diabetes completed the study. After 12 weeks, the mean change in weight was -10.3 kg (95% CI -12.8 to -7.7 kg) in the tirzepatide group and -0.7 kg (95% CI -1.4 to 2.8 kg) in the placebo group, with an estimated treatment difference of -8.7 kg (95% CI -12.0 to -5.5 kg; P < 0.0001), representing 8.8% weight loss. In the tirzepatide group, 100% and 45% of participants experienced weight loss of ≥5% and ≥10% respectively, compared with 9% and 0% in the placebo group. Tirzepatide improved HbA1c (mean difference -0.4% [95% CI -0.7 to 0.0%] vs. placebo; P = 0.05) and reduced total daily insulin dose (-24.2 units/day tirzepatide and -0.3 units/day placebo; difference from baseline vs. placebo -35.1% [95% CI -46.5 to -21.3%; P = 0.0002]). There were no significant adverse events in either group. Among adults with type 1 diabetes and obesity, tirzepatide was superior to placebo for weight loss over 12 weeks.