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
Warning
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.
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
- shortness of breath
- 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
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
- Acid or sour stomach
- belching
- bloated
- excess air or gas in the stomach or intestines
- full feeling
- heartburn
- indigestion
- loss of appetite
- metallic taste in the mouth
- passing of gas
- stomachache
- stomach upset or pain
- vomiting
- weight loss
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
- metallic taste in mouth
- rash
- runny nose
- sneezing
- stuffy nose
- swollen joints
For Healthcare Professionals
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]
Resources & References
- Detailed information from drugs.com > https://www.drugs.com/sfx/metformin-side-effects.html
- “Product Information. Glucophage (metformin).” Bristol-Myers Squibb, Princeton, NJ.
- “Product Information. Fortamet (metFORMIN).” Physicians Total Care, Tulsa, OK.
- Cerner Multum, Inc. “UK Summary of Product Characteristics.” O 0
- “Product Information. Riomet (metFORMIN).” Ranbaxy Pharmaceuticals, Jacksonville, FL.
- Cerner Multum, Inc. “Australian Product Information.” O 0
- “Product Information. Glumetza (metFORMIN).” Biovail Pharmaceuticals Canada, Mississauga, IA.