If you take Januvia (sitagliptin) and your clinician adds Ozempic, Mounjaro or another GLP-1 medicine, ask whether you should keep taking the Januvia. The American Diabetes Association’s 2026 Standards of Care say using the two classes together is not recommended because the combination adds no glucose-lowering benefit beyond the GLP-1 drug alone. Do not stop either medicine on your own, but make sure someone has made a deliberate decision, because the overlap is easy to miss when prescriptions come from different places or when sitagliptin is hidden inside a combination pill.
Two drugs aimed at the same peptide hormone
Both drug classes work through glucagon-like peptide-1 (GLP-1), a gut hormone that helps the pancreas release insulin after meals. The UniProt record for proglucagon shows GLP-1 is a short peptide cut from a larger precursor protein, the same one that yields glucagon. In the body, natural GLP-1 is quickly broken down by an enzyme called DPP-4, which UniProt describes as trimming two-amino-acid pieces from the front end of circulating peptides, including peptide hormones.
Januvia slows that cleanup. According to the Januvia prescribing information, sitagliptin is a DPP-4 inhibitor that raises levels of the body’s own active incretin hormones, GLP-1 and GIP. Ozempic takes a different route. The Ozempic label describes semaglutide as a GLP-1 analogue with 94% sequence homology to human GLP-1 that directly activates the GLP-1 receptor, and notes it is modified at position 8 so DPP-4 cannot easily break it down. Once a long-acting, DPP-4-resistant drug is already driving the receptor, there is little left for a DPP-4 inhibitor to add.
What the studies found
A small randomized crossover study in Diabetes, Obesity and Metabolism (2017) tested that idea in 16 people with type 2 diabetes already taking metformin and liraglutide, an older GLP-1 drug. A single sitagliptin tablet before a test meal raised intact GLP-1 by 78.4% and GIP by 90.2%, yet blood sugar, insulin and glucagon after the meal did not change significantly. The authors concluded that GLP-1 receptors had probably already been maximally stimulated, that their findings did not support the combination, and that longer trials were needed.
The evidence is not entirely one-sided. In a 20-week randomized trial in Diabetic Medicine (2012), people whose diabetes was not controlled on sitagliptin plus metformin either added exenatide, a short-acting GLP-1 drug taken twice daily, or switched from sitagliptin to exenatide. Keeping sitagliptin led to a somewhat larger A1C drop, about 0.68 versus 0.38 percentage points. That study used an older, shorter-acting drug than today’s weekly injections. The ADA cites it alongside the 2017 study and a case series when it advises against the combination.
What the guideline says
In Section 9 of the ADA Standards of Care in Diabetes 2026, the association states that GLP-1 receptor agonists, or the dual GIP and GLP-1 receptor agonist tirzepatide, used together with a DPP-4 inhibitor is not recommended, because there is no added glucose-lowering benefit beyond the GLP-1 drug alone. The same section advises avoiding all of these incretin medicines in people with a history of pancreatitis. The Januvia label also carries a pancreatitis warning and notes a higher risk of low blood sugar when sitagliptin is combined with insulin or drugs that push the pancreas to release insulin.
How to check your own medicine list
Sitagliptin is not always labeled as Januvia. MedlinePlus lists combination products that contain it, including Janumet and Janumet XR (with metformin), Steglujan (with ertugliflozin) and Zituvimet (with metformin). Other DPP-4 inhibitors exist too, so the simplest step is to bring every pill bottle, or a current pharmacy printout, to the visit where a GLP-1 medicine is started.
Questions worth asking: Should I stop my DPP-4 pill when I start the GLP-1 medicine, and if so, when? Does my combination pill need to change to a version without sitagliptin? Do any of my other diabetes medicines need adjusting? MedlinePlus advises telling your doctor and pharmacist about every prescription and nonprescription medicine before starting semaglutide, because doses of other medicines may need to change. Any switch should be planned with your prescriber, not made on your own.
By The Everyday Brief · AI-assisted editorial. Drafted with AI research assistance; claims checked against the linked sources (fetched 2026-10-06 PT). Not medical advice.
Sources
- American Diabetes Association Professional Practice Committee. 9. Pharmacologic Approaches to Glycemic Treatment: Standards of Care in Diabetes 2026. Diabetes Care, 2026.
- DailyMed: Januvia (sitagliptin) prescribing information
- DailyMed: Ozempic (semaglutide) prescribing information
- Nauck MA, et al. Addition of a dipeptidyl peptidase-4 inhibitor, sitagliptin, to ongoing therapy with the glucagon-like peptide-1 receptor agonist liraglutide. Diabetes, Obesity and Metabolism, 2017.
- Violante R, et al. A randomized non-inferiority study comparing the addition of exenatide twice daily to sitagliptin or switching from sitagliptin to exenatide twice daily. Diabetic Medicine, 2012.
- MedlinePlus (U.S. National Library of Medicine): Sitagliptin
- MedlinePlus (U.S. National Library of Medicine): Semaglutide Injection
- UniProt: Pro-glucagon, including glucagon-like peptide 1 (P01275)
- UniProt: Dipeptidyl peptidase 4 (P27487)