Short answer: Janumet is sitagliptin, the drug in Januvia, combined with metformin in one tablet.12 Januvia is 100 mg once daily, lowered for reduced kidney function. Janumet is taken twice daily with meals, up to sitagliptin 100 mg and metformin 2,000 mg a day, and is not used with an eGFR below 30. Janumet has a lactic acidosis boxed warning from metformin; Januvia has none.
| Januvia | Janumet | |
|---|---|---|
| What it contains | Sitagliptin, a DPP-4 inhibitor1 | Sitagliptin and metformin2 |
| Approved for | Blood sugar control in adults with type 2 diabetes1 | Blood sugar control in adults with type 2 diabetes2 |
| How taken | 100 mg once daily, with or without food1 | Twice daily with meals; tablets are not split2 |
| Strengths | 25 mg, 50 mg and 100 mg1 | Sitagliptin 50 mg with metformin 500 mg or 1,000 mg2 |
| Kidney limits | 50 mg daily with an eGFR of 30 to under 45; 25 mg daily below 30 or on dialysis1 | Not used with an eGFR below 30; not recommended at 30 to under 452 |
| Side effects in label trials | On its own vs placebo: stuffy or runny nose with sore throat 5.2% vs 3.3%1 | Started with metformin vs placebo: diarrhea 7.5% vs 4.0%, headache 5.9% vs 2.8%2 |
| Low blood sugar with insulin | Added to insulin: 15.5% vs 7.8% on placebo1 | Added to metformin and insulin: 15.3% vs 8.2% on placebo2 |
| Boxed warning | None1 | Lactic acidosis2 |
Both labels carry the sitagliptin warnings: pancreatitis, heart failure seen with two other DPP-4 inhibitors, acute kidney failure, low blood sugar with insulin or a sulfonylurea, serious allergic reactions, severe joint pain and a blistering skin condition called bullous pemphigoid.12 Janumet adds the metformin warnings: lactic acidosis and lower vitamin B12, with stops around some contrast scans and while food and fluids are restricted for surgery. The Janumet label says it is not recommended at an eGFR of 30 to under 45 because those people need a lower sitagliptin dose than the fixed tablet has.2
One trial in the Janumet label had separate arms: diarrhea was 2.8% on sitagliptin alone, 7.7% on metformin alone, 7.5% on the two together and 4.0% on placebo.2 The other numbers above come from separate trials. These numbers come from separate trials with different people, lengths and methods, so they are not a head-to-head comparison. Which, if either, fits is for your prescriber. More detail: Januvia side effects, Janumet side effects, the Januvia and Janumet dosing schedules, the Januvia missed-dose page, and Jardiance vs Januvia: how do the two diabetes tablets differ?.