Metformin Side Effects
Medically reviewed by Drugs.com. Last updated on Feb 11, 2022.
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 suspension extended release, oral tablet, oral tablet extended release, oral tablet extended release 24 hr
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:
- Abdominal or stomach discomfort
- cough or hoarseness
- decreased appetite
- fast or shallow breathing
- fever or chills
- general feeling of discomfort
- lower back or side pain
- muscle pain or cramping
- painful or difficult urination
- blurred vision
- chest discomfort
- cold sweats
- cool, pale skin
- difficult or labored breathing
- fast, irregular, pounding, or racing heartbeat or pulse
- feeling of warmth
- increased hunger
- increased sweating
- redness of the face, neck, arms, and occasionally, upper chest
- slurred speech
- tightness in the chest
- unusual tiredness or weakness
- Behavior change similar to being drunk
- difficulty with concentrating
- 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:
- Acid or sour stomach
- excess air or gas in the stomach or intestines
- full feeling
- loss of appetite
- metallic taste in the mouth
- passing of gas
- stomach upset or pain
- weight loss
- 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
- 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
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]
Common (1% to 10%): Hypoglycemia
Very rare (less than 0.01%): Lactic acidosis[Ref]
Common (1% to 10%): Asthenia, chills, flu syndrome, accidental injury[Ref]
Very rare (less than 0.01%): Liver function test abnormalities, hepatitis[Ref]
Common (1% to 10%): Chest discomfort, flushing, palpitation[Ref]
Common (1% to 10%): Rash, nail disorder, increased sweating
Frequency not reported: Reduction in thyrotropin (TSH) levels[Ref]
Very common (10% or more): Infection (20.5%)[Ref]
Common (1% to 10%): Myalgia[Ref]
Common (1% to 10%): Lightheadedness, taste disturbances[Ref]
Common (1% to 10%): Headache[Ref]
Common (1% to 10%): Rhinitis[Ref]
Frequently asked questions
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Related treatment guides
1. "Product Information. Glucophage (metformin)." Bristol-Myers Squibb (2001):
2. Cerner Multum, Inc. "UK Summary of Product Characteristics." O 0
3. Cerner Multum, Inc. "Australian Product Information." O 0
4. "Product Information. Fortamet (metformin)." Physicians Total Care (2014):
5. "Product Information. Glumetza (metformin)." Biovail Pharmaceuticals Canada (2014):
6. "Product Information. Riomet (metformin)." Ranbaxy Pharmaceuticals (2014):
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.