What the label lists and what reports show
Metformin side effects
Metformin's FDA label lists its adverse reactions in its own words. FAERS holds 410,076 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 nausea (28,616 reports).
- Generic listed
- Boxed warning
Check it at the source: the metformin FDA label on DailyMed (effective September 3, 2026, Granules India Ltd); the FDA FAERS public dashboard.
What does the patient leaflet say about side effects?
From the patient leaflet: What are the side effects of metformin hydrochloride extended-release tablets?Lactic acidosis. Metformin, the active ingredient in metformin hydrochloride extended-release tablets, can cause a rare but serious condition called lactic acidosis (a buildup of an acid in the blood) that can cause death. Lactic acidosis is a medical emergency and must be treated in the hospital. Call your doctor right away if you have any of the following symptoms, which could be signs of lactic acidosis: you feel cold in your hands or feet you feel dizzy or lightheaded you have a slow or irregular heartbeat you feel very weak or tired you have trouble breathing you feel sleepy or drowsy you have stomach pains, nausea or vomiting Most people who have had lactic acidosis with metformin have other things that, combined with the metformin, led to the lactic acidosis. […]
Source: FDA drug label (Metformin Hydrochloride), Unichem Pharmaceuticals (USA), Inc., effective July 1, 2026 (SPL set 9eebed09-2562-4d21-b3b3-c06562fe3f99), via openFDA; the full label on DailyMed
What does the label list?
From the label: adverse reactionsThe following adverse reactions are discussed in more detail in other sections of the labeling: Lactic Acidosis [see Boxed Warning and Warnings and Precautions (5.1) ] Vitamin B 12 Deficiency [see Warnings and Precautions (5.2) ] Hypoglycemia [see Warnings and Precautions (5.3) ] Adverse reactions occurring >5% in metformin hydrochloride extended-release tablets clinical trials: hypoglycemia, diarrhea, and nausea. ( 6.1 ) To report SUSPECTED ADVERSE REACTIONS, contact Granules Pharmaceuticals Inc at 1-877-770-3183 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. …
Table 1: Adverse Reactions from Clinical Trials of metformin hydrochloride tablets Occurring >5% and More Common than Placebo in Patients with Type 2 Diabetes Mellitus
This table is printed in the Metformin Hydrochloride label published by Unichem Pharmaceuticals (USA), Inc. of July 1, 2026; the label quoted above does not print one.
| Reaction | Metformin Hydrochloride Tablets (n=141) | Placebo (n=145) |
|---|---|---|
| Diarrhea | 53% | 12% |
| Nausea/Vomiting | 26 % | 8% |
| Flatulence | 12% | 6% |
| Asthenia | 9% | 6% |
| Indigestion | 7% | 4% |
| Abdominal Discomfort | 6% | 5% |
| Headache | 6% | 5% |
Rows and numbers as the label prints them, under its own column headings (the first rows of a longer table where it runs on). A reaction in a trial table is not necessarily caused by the medicine, and trials differ from everyday use.
Source: FDA drug label, Granules India Ltd, effective September 3, 2026 (SPL set 73197cb5-3e23-4ac0-b189-f9bc848bce66), via openFDA; the full label on DailyMed
What do FAERS reports show?
410,076 reports list metformin among the medicines taken, each a report of something that happened, not proof the medicine caused it; 33,853 are coded as a death and 144,551 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 22 reactions below, 9 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: 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