GLP-1 Drugs in Type 1 Diabetes: Weight Loss, Blood Sugar, and Ketoacidosis Risk

Type 1 diabetes is an autoimmune disease. The immune system destroys the cells in the pancreas that make insulin, so people with it must take insulin for life. GLP-1 drugs were built for type 2 diabetes, where the body still makes insulin but does not use it well.

No GLP-1 drug is approved by the FDA for type 1 diabetes. Ozempic and Mounjaro are approved only for type 2 diabetes. Wegovy and Zepbound are approved for weight loss. The Wegovy label says its use "in patients with type 1 diabetes mellitus or in combination with insulin has not been evaluated." When a doctor prescribes a drug for a use the FDA has not approved, that is called off-label use. It is legal and common, but it means the drug maker has not shown the FDA that the benefits outweigh the risks for that group.

Off-label use is growing anyway, partly because weight gain is common in type 1 diabetes. A Johns Hopkins team used health records from 33 U.S. health systems and found that obesity among adults with type 1 diabetes rose from 30.5% in 2008-2011 to 38.1% in 2020-2023. Among adults with type 1 diabetes and severe obesity, the share with a GLP-1 prescription rose from 4.5% to 33.1% over the same years. Semaglutide accounted for 45.4% of GLP-1 prescriptions among adults with type 1 diabetes in 2020-2023. Use is lower elsewhere. In Sweden, 5.5% of adults with type 1 diabetes filled a GLP-1 prescription in 2024, according to a national registry study.

The American Diabetes Association notes that pramlintide, a man-made version of amylin, is approved as an add-on to insulin for adults with type 1 diabetes. Amylin is another hormone made by the same cells that make insulin. In trials it lowered HbA1c by 0.3 to 0.4 points and weight by about 1 to 2 kg. HbA1c is a blood test that reflects average blood sugar over about three months.

The largest trials of a GLP-1 drug in type 1 diabetes tested liraglutide, sold as Victoza and Saxenda. Two placebo-controlled trials, ADJUNCT ONE and ADJUNCT TWO, were published in Diabetes Care in 2016.

ADJUNCT ONE enrolled 1,398 adults for 52 weeks. At the top dose of 1.8 mg, HbA1c fell only 0.20 points more than with placebo. Weight fell 4.9 kg more than with placebo, and insulin doses dropped. But low blood sugar episodes with symptoms were 31% more frequent, and high blood sugar with ketones was more than twice as common at the top dose. ADJUNCT TWO, a 26-week trial in 835 adults whose insulin doses were capped, found much the same pattern. The authors of ADJUNCT ONE wrote that the side effects were "thereby limiting clinical use in this group."

The American Diabetes Association's 2026 Standards of Care sum up the liraglutide trials as showing about a 0.4-point drop in HbA1c and about 5 kg of weight loss. They add that "higher rates of DKA and gastrointestinal side effects have limited their use in type 1 diabetes." The Standards make no recommendation to use GLP-1 drugs in type 1 diabetes. They say that small studies of semaglutide and tirzepatide suggest benefits for weight and blood sugar, and that larger studies are under way.

The newer drugs cause more weight loss, and the first randomized trials in type 1 diabetes are small. A randomized trial assigns people by chance to the drug or a placebo, which makes it the best way to tell what the drug itself does.

In ADJUST-T1D, published in NEJM Evidence in 2025, 72 adults with type 1 diabetes and a BMI of 30 or more were assigned to weekly semaglutide (up to 1 mg) or placebo for 26 weeks. All used an automated insulin delivery system, a pump linked to a glucose sensor that adjusts insulin on its own. People on semaglutide lost 8.8 kg more than those on placebo, and their HbA1c fell 0.3 points more. The study's main goal combined three targets: more than 70% of the day in a healthy glucose range, less than 4% of the day below it, and at least 5% weight loss. On semaglutide, 36% met all three; on placebo, no one did. Each group had two severe low blood sugar events, and no one had DKA. A follow-up analysis found that daily insulin fell 22.6% on semaglutide, mostly from smaller mealtime doses.

In a 12-week trial of tirzepatide at Sydney's Garvan Institute, published in Diabetes Care's January 2026 issue, 24 adults with a BMI over 30 took tirzepatide at up to 5 mg weekly or a placebo. The tirzepatide group lost 8.7 kg more than the placebo group, about 8.8% of body weight, and needed 35% less insulin. HbA1c dropped 0.4 points more, a result at the edge of statistical significance. The authors reported no significant adverse events, but the trial was very short and very small.

Clinic records point the same way. At the Barbara Davis Center for Diabetes in Colorado, 50 adults on semaglutide lost 9.1% of their weight over a year and 50 on tirzepatide lost 21.4%, while matched patients not taking either drug did not change. A 2026 pooled analysis of 13 studies of GLP-1 drugs in people with type 1 diabetes and overweight found average weight loss of 4.31 kg and an HbA1c drop of 0.25 points.

On October 28, 2026, researchers from Genentech, Roche, and several U.S. diabetes centers reported a Phase 2 trial of acmopatide (CT-868) in Diabetes Care. It is a daily injection that acts on both the GLP-1 and GIP receptors. The 111 adults in the trial had type 1 diabetes and a BMI of 27 or more. Over 16 weeks, weight fell 3.3% to 6.7% across three doses, compared with a 0.3% gain on placebo. The drop in HbA1c beyond placebo was small: 0.3 points at the middle dose, the only dose that reached even nominal statistical significance. Insulin doses fell, side effects were mostly stomach-related, and there were no cases of DKA or severe low blood sugar.

Lilly is running the two largest trials so far. SURPASS-T1D-1 is sized for about 905 adults with type 1 diabetes and obesity or overweight, and SURPASS-T1D-2 for about 465. Both measure the change in HbA1c at 40 weeks. ClinicalTrials.gov lists both as active but no longer recruiting, with primary completion expected in November 2026.

DKA, or diabetic ketoacidosis, is a life-threatening problem that happens when the body does not have enough insulin. It breaks down fat too fast for fuel, and acids called ketones build up in the blood. People with type 1 diabetes are at risk because their bodies make little or no insulin of their own.

GLP-1 drugs can push insulin needs down quickly. In the ADJUST-T1D follow-up, 83% of the drop in insulin at four weeks came from the drug itself rather than from weight loss, and daily carbohydrates fell from 137 g to 107 g. Eating less and taking less insulin are both expected on these drugs. The concern is insulin falling too low. That is why the Barbara Davis Center authors called for "close supervision on insulin dose changes" when these drugs are prescribed off-label in type 1 diabetes.

Ketones can also build up when blood sugar looks normal. In a McGill University crossover trial of semaglutide with automated insulin delivery, no one developed DKA, but there were two episodes of repeated ketosis (raised ketones without acid buildup) with normal blood sugar while people were on semaglutide. A glucose sensor measures sugar, not ketones, so it would not catch this.

Low blood sugar is the other risk. In the pooled analysis, the odds of low blood sugar episodes were 34% higher with GLP-1 drugs. In a survey of 230 Barbara Davis Center patients taking one of the drugs off-label, 29% of tirzepatide users reported low blood sugar with symptoms, compared with 13.4% of semaglutide users. Nausea and vomiting were more common on GLP-1 drugs in the pooled analysis too. That matters in type 1 diabetes because nausea, vomiting, and stomach pain are also symptoms of DKA, according to MedlinePlus, so a common side effect can hide a dangerous one. Ketones can be checked with a urine or blood test. Our guide to GLP-1 nausea covers the stomach side effects in general.

Heart disease is the leading cause of death in diabetes, and one reason for interest in these drugs is their record in type 2 diabetes. In March 2026, Johns Hopkins researchers reported in Nature Medicine on health records from 174,678 people with type 1 diabetes treated between 2013 and 2024. Over five years, people who started a GLP-1 drug had a 4.3% risk of a major heart event, such as a heart attack or stroke, compared with 5.0% in similar people who did not. The risk of kidney failure was 1.6% versus 1.9%. The study found no rise in hospital stays for DKA or severe low blood sugar.

That is a records study. It can show a link but cannot prove the drugs caused the difference, because people who get these prescriptions may differ in ways the data do not capture. For more on GLP-1 drugs and kidney disease in general, see our kidney disease guide.

A separate problem is type 1 diabetes that has not been diagnosed yet. It can start in adulthood. In a 2026 case report in Frontiers in Endocrinology, doctors at Zhongnan Hospital of Wuhan University described a 28-year-old man with obesity who injected tirzepatide on his own and lost 15 kg in about three months. He was then diagnosed with autoimmune type 1 diabetes and arrived in DKA, with an HbA1c of 10.8%. The authors say one case cannot show that tirzepatide caused or triggered the diabetes, and his high HbA1c suggests his blood sugar had been high for a while. Their advice to doctors is to consider autoimmune diabetes when someone on a self-directed weight-loss drug has unexplained high blood sugar, keeps losing weight, or develops ketoacidosis.

For people with type 1 diabetes, the decision to try a GLP-1 drug belongs with an endocrinologist or diabetes team who can watch insulin closely. Do not cut or stop insulin on your own. Questions worth asking:

• Is my weight or insulin dose high enough that the possible benefits outweigh the risks, given that no GLP-1 drug is approved for type 1 diabetes?
• How should my basal and mealtime insulin change as I start the drug and each time the dose goes up?
• Should I have a way to test for ketones, and when should I use it, especially if I am vomiting or not eating?
• What low blood sugar alerts should I set on my sensor or pump?
• Will my insurance cover a drug used off-label, and what happens if coverage stops?
• Would joining a clinical trial be an option for me?

Our guides to GLP-1 dosing and missed doses and to how other prescriptions change on a GLP-1 cover related questions.