Sitagliptin / metformin (Janumet, Janumet XR, and others)

How Medicare covers it

Part D (tablets and extended-release tablets taken at home). Part A during a covered inpatient stay. No Part B clinician-administered form in the CMS Part B spending file.

What it treats

An adjunct (add-on) to diet and exercise to improve glycemic control (blood sugar control) in adults with type 2 diabetes mellitus. This entry follows the JANUMET XR extended-release label.

What it is for, in depth

JANUMET XR is a once-daily combination tablet for adults with type 2 diabetes whose blood sugar needs more than diet and exercise alone. It is prescribed for people who need both parts at once — someone starting metformin-based treatment, someone already on metformin who needs sitagliptin added, or someone already taking both who is being switched to the single extended-release tablet (keeping the same total daily dose when switching between JANUMET and JANUMET XR). Kidney function shapes the whole treatment path: eGFR is checked before starting and at least annually after, the drug is not used below an eGFR of 30, and it may need to be stopped around iodinated contrast imaging. The pinned label is the Janumet XR extended-release label, supplied as film-coated tablets in three strengths: 50 mg sitagliptin/500 mg metformin HCl extended-release, 50 mg/1,000 mg, and 100 mg/1,000 mg. The package record matches a wider set in the CMS formulary file: those extended-release combinations (in both orders of naming, including Janumet listings) and the immediate-release 50 mg/500 mg and 50 mg/1,000 mg sitagliptin/metformin tablets, including Zituvimet listings — the immediate-release forms are taken on their own schedules, so follow the directions for the exact form prescribed. The boxed warning about lactic acidosis is the central safety fact for anyone taking this combination.

How it works

JANUMET XR combines two blood-sugar-lowering (antihyperglycemic) medicines with complementary mechanisms of action, as the label's clinical pharmacology section puts it: sitagliptin, a dipeptidyl peptidase-4 (DPP-4) inhibitor, and metformin extended-release, a member of the biguanide class. The label extract for this product does not go further than that description of how the two parts work, so this page does not add a deeper mechanism from other sources. The practical idea stated in the label is that the two different-acting medicines are combined in one tablet to improve blood sugar control in adults with type 2 diabetes.

How it is taken

Extended-release tablets by mouth, once daily with a meal; patients taking two JANUMET XR tablets should take them together. The dose is individualized based on the patient's current regimen, effectiveness, and tolerability, and the maximum recommended daily dose is 100 mg of sitagliptin and 2,000 mg of metformin HCl extended-release. The recommended starting dose in patients not currently treated with metformin is 100 mg sitagliptin and 1,000 mg metformin HCl once daily, with gradual dose escalation to reduce the gastrointestinal effects due to metformin. For patients already treated with metformin, the starting dose should provide sitagliptin 100 mg and the metformin dose already being taken, given once daily; for patients taking metformin HCl 850 mg twice daily or 1,000 mg twice daily, the recommended starting dose is two 50 mg sitagliptin/1,000 mg metformin HCl extended-release tablets once daily. Keep the same total daily dose of sitagliptin and metformin when changing between JANUMET and JANUMET XR. Kidney function (eGFR) must be assessed before starting: do not use if eGFR is below 30 mL/min/1.73 m2, initiation is not recommended if eGFR is between 30 and 45, and if eGFR later falls below 45 the sitagliptin dose should be limited to 50 mg once daily. JANUMET XR may need to be discontinued at the time of, or before, iodinated contrast imaging procedures.

Common side effects

The FDA label extract for this product does not list common side effects with percentage rates. Its adverse reactions section does not give a table of frequent effects; instead, it lists the reactions that are discussed elsewhere in the labeling — lactic acidosis, pancreatitis, heart failure, acute renal failure, vitamin B12 deficiency, hypoglycemia (low blood sugar) when combined with insulin or insulin secretagogues, hypersensitivity (allergy) reactions, severe and disabling arthralgia (joint pain), and bullous pemphigoid (a blistering skin condition). The one everyday effect the extract does mention, in the dosage section, is the gastrointestinal effects due to metformin, which is why gradual dose escalation is recommended when starting. Because the extract gives no common-effects rates, this page does not fill them in from other sources.

Serious warnings

JANUMET XR has a boxed warning for metformin-associated lactic acidosis (see boxed_warning). Beyond that, the label warns about: pancreatitis — postmarketing reports include fatal and non-fatal hemorrhagic or necrotizing pancreatitis in patients treated with sitagliptin, and JANUMET XR should be promptly discontinued if pancreatitis is suspected; heart failure, which has been observed with two other members of the DPP-4 inhibitor class, so risks and benefits should be considered in patients with heart failure risk factors and patients monitored for signs and symptoms; acute renal (kidney) failure, reported postmarketing and sometimes requiring dialysis, with kidney function to be assessed before starting and at least annually after; vitamin B12 deficiency, because metformin may lower B12 levels (blood parameters yearly and B12 every 2 to 3 years); hypoglycemia when used with insulin or an insulin secretagogue, where a lower dose of the insulin or secretagogue may be required; serious hypersensitivity reactions with sitagliptin, including anaphylaxis, angioedema, and exfoliative skin conditions including Stevens-Johnson syndrome — stop the drug promptly if these occur; severe and disabling joint pain reported with DPP-4 inhibitors; and bullous pemphigoid, reported postmarketing with DPP-4 inhibitors and sometimes requiring hospitalization — patients should report blisters or erosions, and the drug should be stopped if it is suspected.

Boxed warning

Postmarketing cases of metformin-associated lactic acidosis have resulted in death, hypothermia (low body temperature), hypotension (low blood pressure), and resistant bradyarrhythmias (slow heart rhythms that do not respond to treatment). The onset is often subtle, with only nonspecific symptoms such as malaise (feeling unwell), myalgias (muscle pain), respiratory distress, somnolence (sleepiness), and abdominal pain. In the reported cases, blood lactate was elevated (above 5 mmol/Liter), there was anion gap acidosis without ketonuria or ketonemia, an increased lactate/pyruvate ratio, and metformin plasma levels generally above 5 mcg/mL. Risk factors include renal (kidney) impairment, use of certain other drugs (for example, carbonic anhydrase inhibitors such as topiramate), age 65 or older, a radiological study with contrast, surgery and other procedures, hypoxic states (such as acute congestive heart failure), excessive alcohol intake, hepatic (liver) impairment, and mitochondrial diseases. If metformin-associated lactic acidosis is suspected, JANUMET XR should be stopped immediately and general supportive measures started in a hospital setting; prompt hemodialysis is recommended.

Who should be careful

You must NOT take JANUMET XR if you have severe renal impairment (eGFR below 30 mL/min/1.73 m2), if you have acute or chronic metabolic acidosis including diabetic ketoacidosis, or if you have a history of a serious hypersensitivity reaction to JANUMET XR, sitagliptin, or metformin, such as anaphylaxis or angioedema — those are the label's contraindications. Be careful and expect extra monitoring if your eGFR is between 30 and 45 (starting is not recommended there, and the sitagliptin dose is limited to 50 mg once daily if eGFR falls below 45), if you are 65 or older (kidney function should be assessed more frequently in geriatric patients, and age 65 or greater is a lactic acidosis risk factor), if you have liver impairment (the label says to avoid use in hepatic impairment), if you drink alcohol excessively, if you are having a contrast imaging study or surgery, or if you take insulin or an insulin secretagogue. Premenopausal females should be advised of the potential for an unintended pregnancy, per the label's populations section.

Major interactions

The interaction warning in this label extract is about lactic acidosis risk: using JANUMET XR with specific other drugs may increase the risk of metformin-associated lactic acidosis — namely drugs that impair renal (kidney) function, result in significant hemodynamic change (a big change in blood flow/blood pressure), interfere with acid-base balance, or increase metformin accumulation — so more frequent monitoring of patients should be considered. The boxed warning names one example group: carbonic anhydrase inhibitors such as topiramate are a risk factor for lactic acidosis. The warnings section adds a related combination point: using JANUMET XR together with insulin or an insulin secretagogue (a drug that makes the body release insulin) raises the risk of hypoglycemia (low blood sugar), and a lower dose of the insulin or secretagogue may be required. The label extract does not list a longer table of specific interacting drugs, so tell your prescriber about every medicine you take, especially kidney-affecting drugs and diabetes drugs.

Cost and saving notes

Medicare facts: sitagliptin/metformin is sold under the brand names Janumet and Janumet XR and in generic forms (the package record's formulary matches include generic extended-release and regular tablets, including a Zituvimet listing), so ask whether a generic form is the lower-cost option on your plan. In the package record's 2027 CMS formulary file, the most common (modal) tier for sitagliptin/metformin was tier 3. If your own Part D plan places it on a higher tier than expected, you or your prescriber can ask the plan for a tier exception when the lower-tier options would not work as well for you. If you qualify for Extra Help (the Part D Low-Income Subsidy), your premiums and copays drop a lot. In 2027, what you pay out of pocket for covered Part D drugs is capped at $2,400 for the year, and the Medicare Prescription Payment Plan lets you spread those costs into monthly payments instead of paying large amounts at the pharmacy counter. Ask your pharmacist or your plan what you would actually pay before you fill.

Why it is in its tier

Sitagliptin / metformin (Janumet, Janumet XR, and others) sits on Tier 3 in 91.26% of the plans that list it (5015 of 5495 listing plans). Tier 3 is the preferred brand tier — mid-level copays or coinsurance. The data-visible drivers: It is sold both as a brand product and in generic form, and the CMS dashboard puts its average Part D spending at about $4,451 per beneficiary for 2024 — a mid-cost drug, which matches where plans place it. It is listed by 100.0% of Part D plans. The tier shown is the most common one; individual plans vary.

Sources

• JANUMET XR (SITAGLIPTIN AND METFORMIN HYDROCHLORIDE) TABLET, FILM COATED, EXTENDED RELEASE [MERCK SHARP & DOHME LLC] — DailyMed
• MedlinePlus — Sitagliptin

What official patient guides say

Sitagliptin comes as a tablet to take by mouth, at around the same time every day, with or without food. Take it exactly as directed — do not take more, less, or take it more often than prescribed by your doctor. Sitagliptin helps to control high blood sugar but does not cure diabetes. Continue to take it even if you feel well, and do not stop taking it without talking to your doctor. If you miss a dose, take it as soon as you remember. If it is almost time for the next dose, skip the missed dose and go back to your regular schedule. Do not take a double dose. Keep the tablets in the container they came in, tightly closed and out of reach of children. Store them at room temperature, away from extra heat and moisture, and not in the bathroom.

Source: MedlinePlus — Sitagliptin

Part D formulary coverage

Source: CMS Prescription Drug Plan Formulary, Pharmacy Network, and Pricing Information Files — Monthly file 2026-10-15 (plan year 2027), file 2027_20261008.zip (data.cms.gov dataset ed1496ea-23e7-41f1-9292-172fa842ccfb): basic drugs formulary file + plan information file, both dated 20261031 inside the zip; downloaded and aggregated 2026-10-30. Medication RxCUI sets resolved through the NLM RxNav (RxNorm) API.

What you pay

Without insurance, the cash benchmark is $5.2788 per unit (JANUMET 50-1,000 MG TABLET) — about $158.36 for 30 units. NADAC benchmark — the average price pharmacies pay (CMS, as of 2026-11-04). Pharmacy shelf prices vary.

A tier is not a price; what you pay depends on your plan, pharmacy, and benefit stage; Extra Help or Medicaid can lower it further.

Sources: CMS Plan Benefit Package + formulary data; CMS NADAC · Checked 2026-11-08

Coverage by plan and tier

Of the 5,495 Medicare drug plans we track for 2027, 5,495 list Sitagliptin / metformin (Janumet, Janumet XR, and others) — 100% of plans. Most of those plans put it on Tier 3: 5,015 plans, 91.3% of the plans that list it. Other plans place it on Tier 2 (317 plans), Tier 1 (135 plans) or Tier 6 (20 plans). For example: Aetna Medicare Dual Extra (HMO D-SNP) puts it on Tier 3; Aetna Medicare Dual Extra Care (PPO D-SNP) puts it on Tier 3; Aetna Medicare Value Plus (PPO) puts it on Tier 3. You can compare these plans side by side on our Medicare Advantage hub. A tier is not a price. What you pay also depends on whether you have met your plan's deductible, whether the drug costs a flat copay or a share of the price, and whether you get Extra Help or Medicaid.

Read next

• Part D in 2027: The $700 Deductible, the $2,400 Cap, and the $35 Insulin Rule
• Extra Help in 2027: Lower Drug Copays and Who Qualifies
• Checking Medicare Savings Programs and Extra Help

Part D spending averages (2024)

Source: CMS Medicare Part D Spending by Drug (Drug Spending Dashboard), release RY26 P04 V10, data through 2024 (DSD_PTD_RY26_P04_V10_DY24_BGM.csv), downloaded 2026-10-30

Companies covering this drug

Part D and Medicare Advantage plan sponsors that list this drug on a formulary, 50 at a time.