What the label lists and what reports show
Metformin and pioglitazone side effects
Metformin and pioglitazone's FDA label: “Most common adverse reactions (>5%) are upper respiratory tract infection, edema, diarrhea, headache and weight gain.” FAERS holds 1,321 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 bladder cancer (306 reports).
- Generic listed
- Boxed warning
Check it at the source: the metformin and pioglitazone FDA label on DailyMed (effective December 3, 2025, Bryant Ranch Prepack); 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 pioglitazone and metformin hydrochloride tablets?Pioglitazone and metformin hydrochloride tablets may cause serious side effects, including: • See "What is the most important information I should know about pioglitazone and metformin hydrochloride tablets?" • low blood sugar (hypoglycemia). This can happen if Low blood sugar (hypoglycemia). If you take pioglitazone and metformin hydrochloride tablets 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 take pioglitazone and metformin hydrochloride tablets. Signs and symptoms of low blood sugar may include: o shaking or feeling jittery o sweating o fast heartbeat o change in vision o hunger o headache o change in mood o confusion o dizziness • Liver problems. […]
Source: FDA drug label, ANDA204802 (Macleods Pharms), as published by Bryant Ranch Prepack, effective December 3, 2025 (SPL set 86ca843a-441b-488d-be1d-2576aeee19cf), via openFDA; the full label on DailyMed
What does the label list?
From the label: adverse reactionsMost common adverse reactions (>5%) are upper respiratory tract infection, edema, diarrhea, headache and weight gain.
A table the label prints in its adverse reactions section without a title; its column headings name the groups compared
This table is printed in the Pioglitazone HCL and Metformin HCL label published by Torrent Pharmaceuticals Limited of September 1, 2026; the label quoted above does not print one.
| Reaction | Placebo + Sulfonylurea N=187 | Pioglitazone 15 mg + Sulfonylurea N=184 | Pioglitazone 30 mg + Sulfonylurea N=189 | Pioglitazone 30 mg + Sulfonylurea N=351 | Pioglitazone 45 mg + Sulfonylurea N=351 |
|---|---|---|---|---|---|
| At least one congestive | 2 (1.1%) | 0 | 0 | 1 (0.3%) | 6 (1.7%) |
| Hospitalized | 2 (1.1%) | 0 | 0 | 0 | 2 (0.6%) |
| At least one congestive | 0 | 2 (1.0%) | 2 (1.1%) | 3 (0.9%) | 5 (1.4%) |
| Hospitalized | 0 | 2 (1.0%) | 1 (0.5%) | 1 (0.3%) | 3 (0.9%) |
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.
From the label: adverse reactions, continuedThe following serious adverse reactions are discussed elsewhere in the labeling: • Congestive heart failure [see Boxed Warning, and Warnings and Precautions ( 5.1 )] • Lactic acidosis [see Boxed Warning and Warnings, and Precautions ( 5.2 )] • Edema [see Warnings and Precautions ( 5.3 )] • Fractures [see Warnings and Precautions ( 5.7 )] • Hypoglycemia with Concomitant Use with Insulin or Insulin Secretagogues [see Warnings and Precautions ( 5.4 )] • Hepatic Effects [see Warnings and Precautions ( 5.5 )] • Urinary Bladder Tumors [see Warnings and Precautions ( 5.6 )] • Fractures [see Warnings and Precautions ( 5.7 )] • Macular Edema [see Warnings and Precautions ( 5.8 ] • Vitamin B 12 Levels [see Warnings and Precautions ( 5.9 ] Most common adverse reactions (>5%) are upper respiratory tract infection, edema, diarrhea, headache and weight gain. ( 6.1 ) To report SUSPECTED ADVERSE REACTIONS, contact Macleods Pharma USA, Inc. at 1-888-943-3210 or 1-855-926-3384 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, ANDA204802 (Macleods Pharms), as published by Bryant Ranch Prepack, effective December 3, 2025 (SPL set 86ca843a-441b-488d-be1d-2576aeee19cf), via openFDA; the full label on DailyMed
What do FAERS reports show?
1,321 reports list metformin and pioglitazone among the medicines taken, each a report of something that happened, not proof the medicine caused it; 121 are coded as a death and 258 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 23 reactions below, 10 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 pioglitazone: 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