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Metformin / pioglitazone Side Effects

Medically reviewed by Last updated on May 18, 2023.

Applies to metformin / pioglitazone: oral tablet.


Oral route (Tablet; Tablet, Extended Release)

May cause or worsen congestive heart failure, is not recommended in patients with symptomatic heart failure, and is contraindicated in patients with established NYHA Class III or IV heart failure. Monitor patients for signs and symptoms of heart failure after initiation or dose increases and if heart failure occurs, consider dose reduction or discontinuing metformin/pioglitazone (immediate and extended-release formulations) and manage according to current standards of care. Lactic acidosis can occur due to metformin accumulation during treatment with metformin / pioglitazone (immediate and extended-release formulations) and may result in death, hypothermia, hypotension, and resistant bradyarrhythmias; risk factors include renal impairment, concomitant carbonic anhydrase inhibitor use (eg, topiramate), age 65 years or greater, having a radiological study with contrast, surgery and other procedures, hypoxic states (eg, acute congestive heart failure), excessive alcohol intake, and hepatic impairment. Onset is often subtle with nonspecific symptoms such as malaise, myalgias, respiratory distress, somnolence, and abdominal pain; laboratory abnormalities include elevated blood lactate (greater than 5 mmol/L), anion gap acidosis (without ketonuria or ketonemia), increased lactate:pyruvate ratio, and metformin levels generally greater than 5 mcg/mL. If acidosis is suspected, discontinue treatment, hospitalize the patient immediately, and promptly initiate hemodialysis.

Serious side effects

Along with its needed effects, metformin / pioglitazone may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking metformin / pioglitazone:

More common

Less common


Other side effects

Some side effects of metformin / pioglitazone may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common

For Healthcare Professionals

Applies to metformin / pioglitazone: oral tablet, oral tablet extended release.



Common (1% to 10%): Edema


Very common (10% or more): Edema (26.7%)

Common (1% to 10%): Cardiac failure, chest pain[Ref]

Thiazolidinediones, including pioglitazone can cause dose-related fluid retention which can cause or exacerbate congestive heart failure in some patients. Combination with insulin and use in patients with NYHA Class I and II congestive heart failure may increase risk.[Ref]



Very common (10% or more): Abdominal pain, diarrhea, loss of appetite, nausea, vomiting

Uncommon (0.1% to 1%): Flatulence


Very common (10% or more): Abdominal pain, diarrhea, loss of appetite, nausea, vomiting[Ref]

Gastrointestinal events occur most frequently during initiation of therapy and resolve spontaneously in most cases.[Ref]



Common (1% to 10%): Anemia

Very rare (less than 0.01%): Vitamin B12 absorption decreased, lactic acidosis


Very rare (less than 0.01%): Vitamin B12 absorption decreased, lactic acidosis[Ref]



Common (1% to 10%): Weight increased


Very common (10% or more): Hypoglycemia (27.3%)

Common (1% to 10%): Weight gain[Ref]

Mean weight increase in patients receiving pioglitazone monotherapy for 1 year was 2 to 3 kg. In combination with metformin, mean weight increase over 1 year was 1.5 kg. The mechanism of weight gain is unclear, but probably involves a combination of fluid retention and fat accumulation.[Ref]



Common (1% to 10%): Upper respiratory infection

Uncommon (0.1% to 1%): Sinusitis


Common (1% to 10%): Upper respiratory infection, pharyngitis

Uncommon (0.1% to 1%): Sinusitis[Ref]

Nervous system


Common (1% to 10%): Hypoesthesia, headache, taste disturbance

Uncommon (0.1% to 1%): Insomnia


Common (1% to 10%): Taste disturbance


Common (1% to 10%): Hypoesthesia, headache[Ref]



Common (1% to 10%): Visual disturbances

Postmarketing reports: Macular edema


Common (1% to 10%): Visual disturbances

Frequency not reported: Macular edema[Ref]

Visual disturbances have been reported early in treatment and may be related to changes in blood glucose due to temporary alteration in the turgidity and refractive index of the lens. Macular edema has been reported postmarketing in patients taking pioglitazone or another thiazolidinedione. Some patients presented with blurred vision or decreased visual acuity, although some were diagnosed on routine ophthalmologic examination. Most patients had peripheral edema at time of diagnosis. Some patients improved with drug discontinuation.[Ref]



Very rare (less than 0.01%): Erythema, pruritus, urticaria


Very rare (less than 0.01%): Erythema, pruritus, urticaria[Ref]


Common (1% to 10%): Erectile dysfunction[Ref]


The most commonly reported adverse events included upper respiratory tract infection, edema, diarrhea, headache, and weight gain.[Ref]


There have been postmarketing reports of hepatic failure, including fatalities, in patients taking pioglitazone. The reports contain insufficient information to establish causality.[Ref]


Frequency not reported: Hepatitis, alanine aminotransferase increased, abnormal liver function tests


Frequency not reported: Hepatitis, abnormal liver function tests


Frequency not reported: Alanine aminotransferase increased

Postmarketing reports: Hepatic failure[Ref]



Common (1% to 10%): Bone fracture, arthralgia


Common (1% to 10%): Bone fracture, myalgia, extremity pain, back pain

Uncommon (0.1% to 1%): Serum creatine phosphokinase elevations[Ref]

In pooled analysis of bone fractures in 8100 patients receiving pioglitazone and 7400 receiving comparator treatment; a higher rate of fractures was observed in women receiving pioglitazone (2.6% versus 1.7%). Some epidemiologic studies have suggested a similarly increased risk of fracture in men.[Ref]



Uncommon (0.1% to 1%): Bladder cancer


Uncommon (0.1% to 1%): Bladder cancer[Ref]

The US FDA has released results of its review of pioglitazone and bladder cancer and concluded that the data suggests use of this drug may be linked to an increase risk of bladder cancer. A 10-year prospective cohort study in diabetic patients performed by the manufacturer (n=158,918 never users; n=34,181 ever users) identified 1075 newly diagnosed cases of bladder cancer in never users and 186 cases in ever users. The fully adjusted hazard ratio (HR) showed pioglitazone use was not associated with an increased risk (HR 1.06 (95% confidence interval 0.89 to 1.26). And while a modest trend towards higher risk with increasing duration was observed, this trend was not statistically significant. Compared to the interim 5-year results, the 10-year results found weaker associations that were not statistically significant. However, there are studies that have shown a statistically significant association between exposure to this drug and bladder cancer and an association between cumulative dose or cumulative duration of exposure and bladder cancer. Overall, this drug may be associated with an increase in the risk of urinary bladder tumors, however there is insufficient data to determine whether this drug is a tumor promoter for urinary bladder tumors.[Ref]


Common (1% to 10%): Hematuria[Ref]



Postmarketing reports: Hypersensitivity and allergic reactions (anaphylaxis, angioedema, and urticaria)


Postmarketing reports: Hypersensitivity and allergic reactions (anaphylaxis, angioedema, and urticaria)[Ref]


1. Product Information. Actoplus Met (metformin-pioglitazone). Takeda Pharmaceuticals America. 2005.

2. Cerner Multum, Inc. UK Summary of Product Characteristics.

3. US Food and Drug Administration. Updated FDA review concludes that use of type 2 diabetes medicine pioglitazone may be linked to an increased risk of bladder cancer. 2016.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.