What the label lists and what reports show
Metformin and sitagliptin side effects
Metformin and sitagliptin's FDA label: “The most common adverse reactions reported in ≥5% of patients simultaneously started on sitagliptin and metformin and more commonly than in patients treated with placebo were diarrhea, upper respiratory tract infection, and headache.” FAERS holds 21,442 reports naming it through July 30, 2026; the reaction reported most often, leaving out the conditions it is used for, product-use terms and outcomes, is blood glucose increased (1,506 reports).
- Generic listed
- Boxed warning
Check it at the source: the metformin and sitagliptin FDA label on DailyMed (effective August 11, 2026, Merck Sharp & Dohme LLC); the FDA FAERS public dashboard.
What does the patient leaflet say about side effects?
From the patient leaflet: What are the possible side effects of JANUMET XR?JANUMET XR may cause serious side effects, including: See " What is the most important information I should know about JANUMET XR? ". Kidney problems, sometimes requiring dialysis. Low vitamin B 12 (vitamin B 12 deficiency). Using metformin for long periods of time may cause a decrease in the amount of vitamin B 12 in your blood, especially if you have had low vitamin B 12 blood levels before. Your doctormay do blood tests to check your vitamin B 12 levels. Low blood sugar (hypoglycemia). If you take JANUMET XR with another medicine that can cause low blood sugar, such as a sulfonylurea or insulin, your risk of getting low blood sugar is higher. The dose of your sulfonylurea medicine or insulin may need to be lowered while you use JANUMET XR. […]
Source: FDA drug label, Merck Sharp & Dohme LLC, effective August 11, 2026 (SPL set 64beb3d2-3aeb-4cd5-ba11-dacf6c9a5b50), via openFDA; the full label on DailyMed
What does the label list?
From the label: adverse reactionsThe most common adverse reactions reported in ≥5% of patients simultaneously started on sitagliptin and metformin and more commonly than in patients treated with placebo were diarrhea, upper respiratory tract infection, and headache.
From the label: adverse reactions, continuedThe following adverse reactions are also discussed elsewhere in the labeling: Lactic Acidosis [see Warnings and Precautions (5.1) ] Pancreatitis [see Warnings and Precautions (5.2) ] Heart Failure [see Warnings and Precautions (5.3) ] Acute Renal Failure [see Warnings and Precautions (5.4) ] Vitamin B 12 Deficiency [see Warnings and Precautions (5.5) ] Hypoglycemia with Concomitant Use with Insulin or Insulin Secretagogues [see Warnings and Precautions (5.6) ] Hypersensitivity Reactions [see Warnings and Precautions (5.7) ] Severe and Disabling Arthralgia [see Warnings and Precautions (5.8) ] Bullous Pemphigoid [see Warnings and Precautions (5.9) ] The most common adverse reactions reported in ≥5% of patients simultaneously started on sitagliptin and metformin and more commonly than in patients treated with placebo were diarrhea, upper respiratory tract infection, and headache. ( 6.1 ) To report SUSPECTED ADVERSE REACTIONS, contact Merck Sharp & Dohme LLC at 1-877-888-4231 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch. 6.1 Clinical Trials Experience Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice.
Source: FDA drug label, Merck Sharp & Dohme LLC, effective August 11, 2026 (SPL set 64beb3d2-3aeb-4cd5-ba11-dacf6c9a5b50), via openFDA; the full label on DailyMed
What do FAERS reports show?
21,442 reports list metformin and sitagliptin among the medicines taken, each a report of something that happened, not proof the medicine caused it; 2,107 are coded as a death and 6,972 as a hospital stay. Counts follow how widely a medicine is used and watched, and they are not a measure of how risky it is. Of the 18 reactions below, 8 are named by the same term (in US spelling) in the label's adverse reactions, warnings or patient leaflet; a reaction the label does not name may still be there under another word, and a report does not show that the medicine caused it.
Reports received each year
The 25 most reported reactions
Source: FDA Adverse Event Reporting System (FAERS) via openFDA, reports through July 30, 2026; reactions as MedDRA preferred terms
What next?
- Metformin and sitagliptin: the full record
- label, generics, price, shortages, recalls
- Report a side effect to the FDA
- MedWatch
- Side effects hub
- the most reported medicines and reactions