Can type 2 diabetes medications be used for people with type 1 diabetes?

Recently, I was approached by a colleague who had seen a patient with type 1 diabetes using a glucagon-like peptide-1 (GLP-1) receptor agonist in combination with basal bolus insulin to manage their glucose levels. My colleague was confused by the addition of this medication, as one of the mechanisms of GLP-1 agonists is to stimulate the beta-cells of the pancreas to produce insulin, and these agents are indicated for people with type 2 diabetes.After conducting some research, I sent my colleague a summary of the evidence supporting the use of three type 2 diabetes medications/medication classes that may be considered in people with type 1 diabetes. I told my colleague that, in general, patients with type 1 diabetes may be started on medications typically reserved for those with type 2 diabetes to help reduce the amount of insulin they require. This may help lessen the risks of hypoglycemia and weight gain, and help stabilize glucose levels.1Patients with type 1 diabetes may develop insulin resistance, which is more common in patients with type 2 diabetes. Insulin resistance in type 1 diabetes historically has been confused with glucose toxicity due to chronic hyperglycemia. It can develop early and generally results from combined impairment of insulin sensitivity (need for higher insulin concentrations) and insulin responsiveness. Other factors may be involved, such as lipotoxicity, low grade inflammation, peripheral hyperinsulinemia and hyperglucagonemia.2Type 2 diabetes meds that may be used in type 1 diabetesUse of the medications described below for patients with type 1 diabetes is considered off-label use by Health Canada and should only be recommended by a specialist.1. Metformin1-6Metformin displays significant glucose-lowering and insulin-sensitizing properties. It helps to reduce hepatic gluconeogenesis, stimulate glucose disposal in muscle and improve lipid metabolism. Through these mechanisms, metformin has shown a reduction in insulin requirements, improvements in glycated hemoglobin (A1C), a reduction in whole-body insulin resistance, reduced body weight and improvements to vascular health when added to insulin therapy in patients with type 1 diabetes. In other words, it helps the body better respond to exogenous insulin.Metformin does increase the risk of gastrointestinal (GI) side effects; however, no increased incidence of diabetic ketoacidosis (DKA) or hypoglycemia has been seen when it is used in patients with type 1 diabetes receiving insulin. To help reduce the risk of GI side effects, try adjusting the dose gradually and suggest that patients take it at mealtime.2. SGLT2 inhibitors1,4,6-8Sodium-glucose cotransporter-2 (SGLT2) inhibitors (canagliflozin, empagliflozin, dapagliflozin) work to increase glucose excretion in the urine by inhibiting the SGLT2 transport protein in the kidneys. They have also been shown to reduce hyperglycemia, decrease glucotoxicity, promote weight loss and reduce systolic blood pressure in patients with type 1 diabetes.In type 1 diabetes, treatment with SGLT2 inhibitors has been shown to reduce insulin requirements, and decrease A1C, body weight and fasting plasma glucose. Currently, it is not known whether SGLT2 inhibitors exhibit the same cardiorenal benefits in patients with type 1 diabetes as in those with type 2 diabetes.The most common side effects are genital infections, such as vaginitis in females and balanitis in males. Adverse effects that may warrant discontinuation include urinary tract or genital infections and euglycemic ketoacidosis.3. GLP-1 receptor agonists1,2,9-12Glucagon-like peptide-1 (GLP-1) receptor agonists (semaglutide, dulaglutide, liraglutide) work to delay gastric emptying and glucose absorption from the intestinal tract, inhibit glucagon secretion and help patients lose weight. These effects may help to improve insulin sensitivity and may have a role in prevention of hyperglucagonemia. In patients with type 1 diabetes, GLP-1 receptor agonists have been shown to contribute to a reduction in A1C, body weight and insulin requirements.Tirzepatide, a dual GLP-1/ glucose-dependent insulinotropic polypeptide (GIP) receptor agonist, may also have benefit in patients with type 1 diabetes, leading to a reduction in insulin dose and weight. In general, if GLP-1 agonists are used in patients with type 1 diabetes, dose escalation schedules are similar to those used in type 2 diabetes, and doses are adjusted based on efficacy and tolerance of side effects.Using these drugs in type 1 diabetes6The medications discussed previously should never be used as initial treatment for type 1 diabetes or used without concomitant insulin therapy. The most recent update to the Diabetes Canada guidelines indicates these agents may be helpful in glucose control, weight loss and insulin resistance. When deciding which agent is best, it is important to look at the risks and benefits for the patient. Metformin has modest effects on A1C and weight loss, and moderate GI adverse effects. SGLT-2 inhibitors have a greater effect on A1C, but patients experience less weight loss and have a higher risk for ketoacidosis. Caution needs to be used if patients are in situations where ketones can develop (e.g., illness, infections, surgery, pump failure). Careful patient monitoring should occur for symptoms of DKA, such as nausea, vomiting and general malaise, keeping in mind that the patient’s glucose levels may not be elevated. GLP-1 agonists offer the greatest weight loss and modest lowering of A1C. However, they have the highest risk for GI side effects. Patients that have gastroparesis may experience further delays in gastric emptying.Initial doses of these drugs are generally the same as those used for patients with type 2 diabetes, but patients may derive benefit from even lower doses. Upon initiation of these medications, patients should be assessed to determine whether insulin doses need to be lowered. For example, a patient may not need a reduction in their insulin dose if their glucose levels are elevated; however, if they are mostly within the target range, they may benefit from a 10%–20% dose reduction. Regardless, patients should be monitored for an increase in hypoglycemia.Medications not recommended in type 1 diabetesI also explained to my colleague that not all drugs for type 2 diabetes are useful as add-ons to insulin in patients with type 1 diabetes. The following three categories of drugs are not recommended in type 1 diabetes.Thiazolidinediones (pioglitazone and rosiglitazone) are used in type 2 diabetes to reduce insulin resistance. In type 1 diabetes, they have been shown to lower A1C and postprandial glucose, but have no effect on fasting plasma glucose, insulin requirements or body mass index. Any potential benefits of these medications in type 1 diabetes would be offset by their side effects, including weight gain, bone fractures and precipitation of congestive heart failure.2,6Acarbose has been studied as an adjunctive therapy in type 1 diabetes. However, it was not found to be beneficial, and patients reported an increased incidence of GI side effects such as flatulence, diarrhea and abdominal pain.1,6Dipeptidyl peptidase 4 (DPP-4) inhibitors (gliptins) have no reported effects on modulating blood glucose in patients with type 1 diabetes.1,6Rhonda Roedler is a pharmacist in Calgary, AB. She maintains an ambulatory clinical practice in diabetes.This article was originally published in print in our sister publication Pharmacy Practice + Business magazine. References:Cai X, Lin C, Yang W, et al. Non-insulin antidiabetes treatment in type 1 diabetes mellitus: a systematic review and meta-analysis. Diabetes Metab J 2021;45:312-25.Apostolopoulou M, Lambadiari V, Roden M, et al. Insulin resistance in type 1 diabetes: pathophysiological, clinical and therapeutic relevance. Endocr Rev 2025;46:317-48.Type 1 BETTER project. Treating type 1 diabetes with insulin…and medication? May 12, 2025. (accessed January 16, 2026).Beysel S, Unsal I, Kizilgul M, et al. The effects of metformin in type 1 diabetes mellitus. BMC Endocr Disord 2018;18:1. DOI 10.1186/s12902-017-0228-9.Xu L, Wang W, Song W. A combination of metformin and insulin improve cardiovascular and cerebrovascular risk factors in individuals with type 1 diabetes mellitus. Diabetes Res Clin Pract 2022;191:110073.Halperin IJ, Wicklow B, Amed S, et al. Glycemic management across the lifespan for people with type 1 diabetes: a clinical practice guideline. Can J Diabetes 2025;49:5-18.Taylor SI, Blau JE, Rother KI, et al. SGLT2 Inhibitors as adjunctive therapy for type 1 diabetes: balancing benefits versus risks. Lancet Diabetes Endocrinol 2019;7(12):949-58.Maffei P, Bettini S, Busetto L, et al. SGLT2 inhibitors in the management of type 1 diabetes (T1D): an update on current evidence and recommendations. Diabetes Metab Syndr Obes 2023;16:3579-98.Lisco G, De Tullio A, Disoteo OE, et al. Incretin-based adjunct to background insulin treatment for managing body weight excess in type 1 diabetes: an expert opinion viewpoint from the Italian association of clinical endocrinologists. Diabetes Metab Res Rev 2025;41:e70073.Park J, Ntelis S, Yunasan E, et al. Glucagon-like peptide 1 analogues as adjunctive therapy for patients with type 1 diabetes: an updated systematic review and meta-analysis. J Clin Endocrinol Metab 2024;109:279-92.Guyton J, Jeon M, Brooks A. Glucagon-like peptide 1 receptor agonists in type 1 diabetes mellitus. Am J Health-Syst Pharm 2019;76:1739-48.Smith JR, Frampton R, Samocha-Bonet D, et al. Tirzepatide in adults with type 1 diabetes: a phase 2 randomized placebo controlled clinical trial. Diabetes Care;49(1):161-70.

Can type 2 diabetes medications be used for people with type 1 diabetes?

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