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Metformin Side Effects

Medically reviewed by Drugs.com. Last updated on Nov 4, 2020.

In Summary

Commonly reported side effects of metformin include: lactic acidosis, diarrhea, nausea, nausea and vomiting, vomiting, and flatulence. Other side effects include: asthenia, and decreased vitamin b12 serum concentrate. See below for a comprehensive list of adverse effects.

For the Consumer

Applies to metformin: oral solution, oral tablet, oral tablet extended release, oral tablet extended release 24 hr

Warning

Oral route (Tablet; Tablet, Extended Release; Solution; Suspension, Extended Release)

Death, hypothermia, hypotension, and resistant bradyarrhythmias have been reported due to metformin-associated lactic acidosis. Onset may be subtle and include nonspecific symptoms such as malaise, myalgia, respiratory distress, somnolence, and abdominal distress; laboratory abnormalities include low pH, increased anion gap and elevated blood lactate. The risk of lactic acidosis increases with renal or hepatic impairment, aged 65 years or older, having a radiological study with contrast, surgery, or other procedures, hypoxic states, and excessive alcohol intake. If lactic acidosis is suspected, metformin hydrochloride should be discontinued, supportive measures started in a hospital setting. Prompt hemodialysis is recommended.

Side effects requiring immediate medical attention

Along with its needed effects, metformin 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:

More common

  • Abdominal or stomach discomfort
  • cough or hoarseness
  • decreased appetite
  • diarrhea
  • fast or shallow breathing
  • fever or chills
  • general feeling of discomfort
  • lower back or side pain
  • muscle pain or cramping
  • painful or difficult urination
  • sleepiness

Less common

  • Anxiety
  • blurred vision
  • chest discomfort
  • cold sweats
  • coma
  • confusion
  • cool, pale skin
  • depression
  • difficult or labored breathing
  • dizziness
  • fast, irregular, pounding, or racing heartbeat or pulse
  • feeling of warmth
  • headache
  • increased hunger
  • increased sweating
  • nausea
  • nervousness
  • nightmares
  • redness of the face, neck, arms, and occasionally, upper chest
  • seizures
  • shakiness
  • slurred speech
  • tightness in the chest
  • unusual tiredness or weakness

Rare

  • Behavior change similar to being drunk
  • difficulty with concentrating
  • drowsiness
  • lack or loss of strength
  • restless sleep
  • unusual sleepiness

Side effects not requiring immediate medical attention

Some side effects of metformin 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

Less common

  • Abnormal stools
  • bad, unusual, or unpleasant (after) taste
  • change in taste
  • difficulty with moving
  • discoloration of the fingernails or toenails
  • flu-like symptoms
  • joint pain
  • rash
  • sneezing
  • stuffy or runny nose
  • swollen joints

For Healthcare Professionals

Applies to metformin: compounding powder, oral solution, oral suspension extended release, oral tablet, oral tablet extended release

General

Gastrointestinal events such as nausea, vomiting, diarrhea, abdominal pain, and loss of appetite have been frequently reported during therapy initiation and resolve spontaneously in most cases.

Adverse events in the pediatric population appear to be similar in nature and severity to that published in adults.[Ref]

Metabolic

Common (1% to 10%): Hypoglycemia

Very rare (less than 0.01%): Lactic acidosis[Ref]

Gastrointestinal

Very common (10% or more): Diarrhea (53.2%), nausea/vomiting (25.5%), flatulence (12.1%)

Common (1% to 10%): Indigestion, abdominal discomfort, abnormal stools, dyspepsia, loss of appetite[Ref]

Hematologic

Very rare (less than 0.01%): Subnormal vitamin B12 levels[Ref]

Other

Common (1% to 10%): Asthenia, chills, flu syndrome, accidental injury[Ref]

Hepatic

Very rare (less than 0.01%): Liver function test abnormalities, hepatitis[Ref]

Cardiovascular

Common (1% to 10%): Chest discomfort, flushing, palpitation[Ref]

Dermatologic

Common (1% to 10%): Rash, nail disorder, increased sweating

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

Endocrine

Frequency not reported: Reduction in thyrotropin (TSH) levels[Ref]

Immunologic

Very common (10% or more): Infection (20.5%)[Ref]

Musculoskeletal

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

Nervous system

Common (1% to 10%): Lightheadedness, taste disturbances[Ref]

Psychiatric

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

Respiratory

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

References

1. "Product Information. Glucophage (metformin)." Bristol-Myers Squibb, Princeton, NJ.

2. "Product Information. Fortamet (metFORMIN)." Physicians Total Care, Tulsa, OK.

3. Cerner Multum, Inc. "UK Summary of Product Characteristics." O 0

4. "Product Information. Riomet (metFORMIN)." Ranbaxy Pharmaceuticals, Jacksonville, FL.

5. Cerner Multum, Inc. "Australian Product Information." O 0

6. "Product Information. Glumetza (metFORMIN)." Biovail Pharmaceuticals Canada, Mississauga, IA.

Frequently asked questions

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.