Should insulin be reduced when starting semaglutide or tirzepatide?

Insulin sometimes needs to be reduced when semaglutide or tirzepatide is started, especially if fasting glucose is already near goal or hypoglycemia is occurring. The decision depends on glucose readings, insulin type, A1C, diet, and medical history.

Can GLP-1 medications replace insulin or metformin?

Sometimes, but not automatically. Some patients may need less insulin or fewer diabetes medications after weight loss and A1C improvement. Others still need ongoing therapy. Diabetes medications should not be stopped without guidance from the treating clinician.

Which diabetes medications require extra caution with GLP-1 medications?

Insulin and sulfonylureas require the most caution because they can increase the risk of hypoglycemia when combined with semaglutide or tirzepatide. DPP-4 inhibitors are also usually not combined with GLP-1 medications because the added benefit is limited.

Can GLP-1 / GLP-1–GIP (semaglutide / tirzepatide) Medications Be Used With Diabetes Medications? (insulin, metformin, & what the evidence shows)

Q: Can semaglutide or tirzepatide be used with diabetes medications?

Yes. Semaglutide and tirzepatide are commonly used with other diabetes medications, including metformin and sometimes insulin. The main safety issue is low blood sugar when they are combined with insulin or medications that stimulate insulin release.

Q: Can you take semaglutide or tirzepatide with insulin?

Yes, but insulin doses may need adjustment. Semaglutide and tirzepatide can lower blood sugar, so combining them with insulin may increase the risk of hypoglycemia. Patients using insulin should monitor glucose closely and work with their treating clinician.

Joshua Silva, MD
2 days ago
5 min read

Medically authored by Joshua Silva, MD | Evidence-Based Weight Loss at Potere Health MD

Yes. GLP-1 receptor agonists (such as semaglutide) and dual GIP/GLP-1 receptor agonists (such as tirzepatide) can be used together with other diabetes medications, including insulin, when clinically appropriate.

The American Diabetes Association (ADA) explicitly supports combining GLP-1–based therapy with insulin in type 2 diabetes, with the important caveat that insulin dosing should be reassessed when GLP-1 therapy is started or intensified.¹

The primary safety issue when these drugs are combined with other diabetes medications is hypoglycemia (low blood sugar), particularly when used with insulin or sulfonylureas. This risk is described in FDA prescribing information for both semaglutide and tirzepatide.²–⁴

“Semaglutide and tirzepatide with metformin and insulin for type 2 diabetes, showing GLP-1 and GLP-1/GIP therapy lowering A1C and blood sugar safely.”

Quick Answer

GLP-1 and GLP-1/GIP medications can be used with most diabetes medications, including metformin and insulin.

However, when combined with insulin or sulfonylureas, dose adjustments and monitoring are often needed to reduce the risk of low blood sugar.¹–⁴

Diabetes medications that are usually safe to continue

Many people worry that starting semaglutide or tirzepatide means they must stop their other diabetes medications. In reality, most type 2 diabetes drugs can be continued safely, and some are routinely used together.

Medications that are generally compatible with GLP-1 and GLP-1/GIP therapy include:

Metformin
Basal insulin (with dose reassessment)¹–⁴
Mealtime insulin (with dose reassessment)¹–⁴

The American Diabetes Association specifically supports combining GLP-1–based therapy with insulin when clinically appropriate, with the recommendation that insulin dosing be reassessed as glucose control improves.¹

Why this question comes up so often

GLP-1 receptor agonists were originally developed and approved as type 2 diabetes treatments. Over time, they have become a core part of modern diabetes care because of their ability to improve blood sugar control and support weight loss. As a result, many patients already taking diabetes medications later start a GLP-1 or GLP-1/GIP medication.¹

Which GLP-1-based medications are included?

This includes:

GLP-1 receptor agonists such as semaglutide
Dual GIP/GLP-1 receptor agonists such as tirzepatide

Both classes are approved for glucose control in type 2 diabetes and have been studied in combination with insulin.¹,⁵,⁶

What happens when these drugs are added to existing diabetes therapy?

Blood sugar control (A1C) improves — with measurable reductions

In randomized trials where GLP-1–based therapy was added to basal insulin, A1C fell substantially compared with placebo:

Tirzepatide added to insulin glargine (SURPASS-5, 40 weeks):

Mean A1C change from baseline at week 40:−2.11% (5 mg), −2.40% (10 mg), −2.34% (15 mg)vs −0.86% with placebo.

Semaglutide added to basal insulin (SUSTAIN-5, 30 weeks):

Mean A1C reductions at week 30 (baseline mean A1C 8.4%):−1.4% (0.5 mg) and −1.8% (1.0 mg)vs −0.1% with placebo.

These trial results support that GLP-1 and GLP-1/GIP medications can provide clinically meaningful A1C improvement even when a patient is already treated with insulin.

Insulin requirements may change

Because glucose control can improve substantially after starting GLP-1/GIP therapy, the ADA recommends that insulin dosing be reassessed when GLP-1–based therapy is initiated or intensified.¹

This aligns with FDA labeling for semaglutide and tirzepatide, which warns that hypoglycemia risk increases when used with insulin (or insulin secretagogues) and that dose reduction of those agents may be needed.²–⁴

Trial	Population/Background Therapy	Timepoint	Active drug (dose)	Mean A1C change	Placebo A1C change
SURPASS-5	T2D on titrated insulin glargine ± metformin	Week 40	Tirzepatide 5 mg	−2.11%	−0.86% (PMC)
			Tirzepatide 10 mg	−2.40%	−0.86% (PMC)
			Tirzepatide 15 mg	−2.34%	−0.86% (PMC)
SUSTAIN-5	T2D on basal insulin ± metformin	Week 30	Semaglutide 0.5 mg	−1.4%	−0.1% (PubMed)
			Semaglutide 1.0 mg	−1.8%	−0.1% (PubMed)

The key safety issue: hypoglycemia

GLP-1 and GIP/GLP-1 medications do not usually cause hypoglycemia by themselves, but they can increase the risk when combined with medications that actively lower glucose, such as insulin or sulfonylureas.

The FDA prescribing information for:

Semaglutide (Ozempic®)²
Tirzepatide (Mounjaro®)³
Tirzepatide (Zepbound®)⁴

all warn that hypoglycemia risk increases when these drugs are used with insulin or insulin secretagogues and recommend considering dose reductions of those agents.

Which diabetes medications require special attention?

Insulin

Insulin is commonly used with GLP-1–based therapy, but:

ADA guidelines recommend reassessing insulin dose when GLP-1 therapy is added or escalated.¹
FDA labeling warns of increased hypoglycemia risk when used together.²–⁴

Sulfonylureas

FDA labeling for both semaglutide and tirzepatide identifies sulfonylureas as medications that increase hypoglycemia risk when combined with GLP-1–based therapy, and dose reductions may be needed.²–⁴

DPP-4 inhibitors

The ADA states that DPP-4 inhibitors should not be used together with GLP-1 or GIP/GLP-1 receptor agonistsbecause the combination does not provide additional benefit.¹

Metformin

Metformin is commonly used alongside GLP-1 and GLP-1/GIP therapy. Unlike insulin and sulfonylureas, metformin does not increase the risk of hypoglycemia, which is why it typically does not require dose adjustment when GLP-1–based therapy is started.¹

Are these dangerous drug interactions?

The main concern is not toxicity or chemical interactions, but excess glucose lowering, which leads to hypoglycemia when insulin or sulfonylureas are not adjusted appropriately.¹–⁴

Who needs closer monitoring?

Based on ADA guidance and FDA labeling, patients who need the most careful monitoring are those who:

Use insulin
Use sulfonylureas
Have a history of hypoglycemia¹–⁴

Bottom line

GLP-1 and GLP-1/GIP medications can be safely combined with other diabetes medications, including insulin, when managed appropriately. The key clinical responsibility is to reassess insulin and sulfonylurea doses to reduce hypoglycemia risk, as recommended by both the ADA and the FDA.¹–⁴

Disclaimer

This article is for educational purposes only and is not a substitute for medical advice.

About the Author

Dr. Joshua Silva, MD, is a licensed physician and Medical Director of Potere Health MD. He earned his medical degree from the University of Hawaiʻi John A. Burns School of Medicine and completed residency training in Occupational and Environmental Medicine at the University of Utah, where he also earned a master’s degree in Occupational Health. He later completed a Master of Business Administration with an emphasis in health care administration at Ohio University.

Dr. Silva specializes in evidence-based weight management, including GLP-1 and GIP therapies such as semaglutide and tirzepatide. He provides in-person and virtual care for patients in Salt Lake City, St. George, and Cedar City, Utah.

Can semaglutide or tirzepatide be used with diabetes medications?

Yes. Semaglutide and tirzepatide can be used with many diabetes medications, including metformin and insulin, when clinically appropriate. The main safety concern is low blood sugar when they are combined with insulin or sulfonylureas.

Can you take semaglutide or tirzepatide with metformin?

Yes. Metformin is commonly continued when starting semaglutide or tirzepatide. Metformin has a low risk of low blood sugar and is often used alongside GLP-1 or GLP-1/GIP medications for type 2 diabetes.

Can you take semaglutide or tirzepatide with insulin?

Yes, but insulin dosing should be reassessed. Semaglutide and tirzepatide can improve blood sugar, so patients using insulin may need closer glucose monitoring and possible dose adjustment to reduce hypoglycemia risk.

Do GLP-1 medications cause low blood sugar?

GLP-1 medications usually have a low risk of low blood sugar when used alone or with metformin. The risk is higher when they are combined with insulin or sulfonylureas.

Which diabetes medications need extra caution with GLP-1 medications?

Insulin and sulfonylureas need the most caution because they can increase hypoglycemia risk. DPP-4 inhibitors are also usually not combined with GLP-1 or GIP/GLP-1 medications because added benefit is limited.

Sources

American Diabetes Association Professional Practice Committee for Diabetes. 9. Pharmacologic approaches to glycemic treatment: Standards of Care in Diabetes—2026. Diabetes Care. 2026;49(Suppl 1):S183-S215. doi:10.2337/dc26-S009. https://pubmed.ncbi.nlm.nih.gov/41358900/
U.S. Food and Drug Administration. Ozempic (semaglutide) injection [prescribing information]. Revised January 2025. https://www.accessdata.fda.gov/drugsatfda_docs/label/2025/209637s025lbl.pdf
U.S. Food and Drug Administration. Mounjaro (tirzepatide) injection [prescribing information]. Revised 2025. https://www.accessdata.fda.gov/drugsatfda_docs/label/2025/215866s039lbl.pdf
U.S. Food and Drug Administration. Zepbound (tirzepatide) injection [prescribing information]. Revised 2025. https://www.accessdata.fda.gov/drugsatfda_docs/label/2025/217806s031lbl.pdf
Dahl D, Onishi Y, Norwood P, et al. Effect of subcutaneous tirzepatide vs placebo added to titrated insulin glargine on glycemic control in patients with type 2 diabetes: The SURPASS-5 randomized clinical trial. JAMA.2022;327(6):534-545. doi:10.1001/jama.2022.0078. https://pubmed.ncbi.nlm.nih.gov/35133415/
Rodbard HW, Lingvay I, Reed J, et al. Semaglutide added to basal insulin in type 2 diabetes (SUSTAIN 5): A randomized, controlled trial. J Clin Endocrinol Metab. 2018;103(6):2291-2301. doi:10.1210/jc.2018-00070. https://pubmed.ncbi.nlm.nih.gov/29688502/