Why the combination needs care
GLP-1 medicines raise insulin release mainly when blood sugar is high, so on their own they rarely push it too low. Injected insulin works regardless of your blood sugar level. When the two are combined, the GLP-1’s effect adds to a dose of insulin that was set before it started, and that is where the risk comes from.
Every diabetes label covered here has a hypoglycemia warning that singles out use with insulin or an insulin secretagogue such as a sulfonylurea, and describes the risk as including severe episodes [1][3][4]. Going the other way carries a different risk: cutting insulin sharply can let blood sugar and ketones rise, which is why the European documents mention ketoacidosis [9].
What each US label says
The wording on the insulin dose is addressed to prescribers and says “consider”. How much, if anything, to change depends on your readings, your targets and your other treatment. Any change to your insulin is a decision for your prescriber, not something the label sets for you.
| Label | Studied with insulin | Insulin dose wording | Injection instructions |
|---|---|---|---|
| Ozempic® injection [1] | Yes, basal insulin (14.1) | Consider reducing (5.5, 7.1) | Separate, never mixed, not adjacent (2.1) |
| Rybelsus® and Ozempic® tablets [2] | Yes, insulin with or without metformin (6.1) | Consider reducing (5.4, 7.1) | Tablet; not applicable |
| Mounjaro® [3] | Yes, insulin glargine, SURPASS-5 (14.4) | Consider reducing (5.3, 7.1) | Separate, never mixed, not adjacent (2.2) |
| Trulicity® [4] | Yes, basal and mealtime insulin (6.1, 14.3) | Consider reducing (5.3, 7.2) | Separate, never mixed, not adjacent (2.4) |
| Victoza® [5] | Yes, insulin detemir added (14.1) | Consider reducing (5.4, 7.2) | Separate, never mixed, not adjacent (2.3) |
| Byetta® [6] (US approval withdrawn 09/2025 [15]) | Yes, insulin glargine (14.3) | Consider reducing (5.3, 7) | Separate, never mixed, not adjacent (2.1) |
| Wegovy® [7] | Not evaluated (5.4) | Consider reducing (5.4, 7.1) | Not described |
| Saxenda® [8] | Weight trial in people on basal insulin (6.1) | Risk may be lowered by reducing (5.4) | Not described |
What the European and Canadian documents add
- Stepwise reduction: the EU product information for Ozempic®, Victoza®, Trulicity® and Mounjaro® says a reduction of insulin may be considered when the GLP-1 is added, that blood glucose self-monitoring is needed to adjust the insulin, and that the reduction should be stepwise [9][10].
- Not a substitute for insulin: the EU documents for semaglutide, liraglutide and dulaglutide say these medicines do not replace insulin and describe ketoacidosis in insulin-dependent patients after insulin was stopped or reduced quickly [9]. The Canadian Trulicity® monograph says the same about substitution and type 1 diabetes [12]. The US labels checked here do not contain that sentence.
- Insulin types: the Canadian Mounjaro® monograph notes that tirzepatide has not been studied with short-acting, intermediate-acting or premixed insulins, and that it is not a substitute for insulin [11].
How the combination was studied
Low blood sugar was counted differently in each trial, so the rates below show what each label reports rather than a fair ranking. In the placebo-controlled trials, investigators managed insulin doses under rules set in advance; those were study procedures, not instructions for patients [1][3][6].
| Label and trial | Design and length | Low blood sugar reported | Severe episodes |
|---|---|---|---|
| Ozempic®, added to basal insulin [1] | 397 people, against placebo, 30 weeks | Confirmed at 56 mg/dL or below, or severe: 5.3% placebo; 8.3% and 10.7% on the two doses | 0% placebo; 0% and 1.5% |
| Mounjaro®, SURPASS-5 [3] | 475 people, added to insulin glargine, against placebo, 40 weeks | Below 54 mg/dL: 13% placebo; 14% to 19% across doses | 0% placebo; 0% to 2% |
| Rybelsus®, added to insulin [2] | Against placebo, 52 weeks | Below 54 mg/dL: 32% placebo; 26% and 30% on the two doses | 1% placebo; 0% and 1% |
| Trulicity®, with mealtime insulin [4] | 884 people, against insulin glargine, 26-week primary endpoint | Below 54 mg/dL in a 52-week trial: 77% and 69% on the two doses | 2.7% and 3.4% |
| Byetta®, added to insulin glargine [6] | 259 people, against placebo, 30 weeks | Any reported episode: 29.5% placebo; 24.8% exenatide | 0.8% placebo; 0% |
| Saxenda®, weight trial on basal insulin [8] | Against placebo | No meaningful difference below 54 mg/dL | 1% placebo; 1.5% |
Two injections, kept apart
- Separate injections: Ozempic®, Mounjaro®, Trulicity®, Victoza® and Byetta® all say the GLP-1 and insulin are given as separate injections [1][3][4][5][6].
- Never mixed: the labels say never to mix the two, and the Ozempic®, Victoza® and Byetta® patient materials repeat it: do not combine them in the same injection [1][5][6].
- Same area is allowed: both can go into the same body region, such as the stomach area, but the injection sites should not be next to each other [1][3].
- No sharing: Ozempic® (5.4), Victoza® (5.3), Byetta® (5.2) and the Mounjaro® KwikPen® (5.10) labels say a pen must never be shared, even with a new needle, because of the risk of passing on blood-borne infections [1][3][5][6].
Other warnings that matter more with insulin
Eyes: the Ozempic® label reports more diabetic retinopathy complications on semaglutide in a two-year trial and notes that a rapid improvement in blood sugar has been associated with temporary worsening (5.3). The Mounjaro® label, updated in 08/2026, says the same about rapid improvement and asks for monitoring of people with a history of retinopathy (5.7) [1][3]. That matters when a GLP-1 and insulin together bring blood sugar down quickly.
Dehydration: vomiting and diarrhea can lead to kidney injury, and the labels ask prescribers to monitor kidney function in people who report them (Ozempic® 5.6, Mounjaro® 5.5) [1][3]. Vomiting also matters for anyone on insulin, because the European documents link quick insulin cuts with ketoacidosis, which itself causes nausea and vomiting [9][14].
What the Medication Guides and NIDDK ask of you
The Ozempic® Medication Guide asks you to talk through low blood sugar, and what to do when it happens, with your provider before the first dose, and to mention every other diabetes medicine you use, insulin included. Its list of signs includes dizziness, blurred vision, sweating, slurred speech, confusion or drowsiness, shakiness, headache and a fast heartbeat [1]. It also asks you to keep a list of your medicines to show each clinician and pharmacist.
The NIH’s diabetes institute, NIDDK, explains that lows come on quickly, can happen during sleep and can go unnoticed, and that alcohol without enough food makes them more likely. It describes treating a low with fast-acting carbohydrate and re-checking, and glucagon for severe lows, and suggests asking your care team about a glucagon kit and teaching family or friends when to use it [13]. Your own plan, including the numbers to act on, comes from your care team.
Ozempic®, Rybelsus®, Wegovy®, Saxenda® and Victoza® are registered trademarks of Novo Nordisk A/S. Mounjaro®, Trulicity® and KwikPen® are registered trademarks of Eli Lilly and Company. Byetta® is a trademark of the AstraZeneca group of companies. PepLabo is not affiliated with or endorsed by Novo Nordisk, Eli Lilly and Company or AstraZeneca.
When to get help
| Sign | Who to contact | How fast | Source |
|---|---|---|---|
| Losing consciousness or having a seizure during a low | Emergency services (911 or your local number); the people around you call after giving glucagon | Emergency | NIDDK [13] |
| Fruity-smelling breath, deep rapid breathing, or nausea and vomiting with diabetes | Emergency services or the emergency room | Emergency | MedlinePlus [14] |
| Low blood sugar episodes that are new or more frequent since starting the GLP-1 | Your prescriber | Today | Ozempic® Medication Guide [1]; Mounjaro® label, section 17 [3] |
| Changes in vision during treatment | Your prescriber | Today | Ozempic® Medication Guide [1]; Mounjaro® label, section 17 [3] |
| Vomiting or diarrhea that keeps you from drinking enough | Your prescriber | Today | US labels, kidney injury warnings [1][3] |
