Based on NIH | Can metformin cause muscle pain, and how do I know if it’s a sign of lactic acidosis?

Metformin can be linked to muscle pain in rare situations, and it can also be one of the warning signs of a serious condition called lactic acidosis. ^[1] Lactic acidosis is an uncommon but urgent complication in which acid (lactate) builds up in the blood, and it requires immediate medical care. ^[2]

Quick answer

• Yes, unusual muscle pain can occur with metformin and is specifically listed as a potential warning sign of lactic acidosis. ^[1]
• If you have unusual muscle pain along with symptoms like severe fatigue, shortness of breath, stomach discomfort, feeling cold, dizziness, or a slow/irregular heartbeat, you should stop metformin and seek urgent medical help. ^{[1] [3]}

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What muscle symptoms matter

• Unusual muscle pain (myalgia) is highlighted in official patient guides as a sign to watch for. ^[1]
• Muscle pain by itself can have many causes (e.g., exercise, statin medicines, viral illness), but with metformin, “unusual muscle pain” is a red-flag symptom when it appears with other warning signs. ^[1]

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Signs that suggest lactic acidosis

• Very weak, tired, or uncomfortable feeling. ^[1]
• Unusual muscle pain. ^[1]
• Trouble breathing. ^[1]
• Unusual or unexpected stomach discomfort, nausea, vomiting, or diarrhea. ^{[1] [4]}
• Feeling cold, especially hands/feet. ^{[1] [2]}
• Feeling dizzy or lightheaded. ^{[1] [2]}
• Suddenly developing a slow or irregular heartbeat. ^[1]

If these symptoms appear, stop metformin and get urgent medical care; lactic acidosis is a medical emergency treated in a hospital and may need hemodialysis to remove metformin. ^{[2] [3] [5]}

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Who is at higher risk

• Kidney problems or sudden dehydration (e.g., vomiting, diarrhea, poor fluid intake). ^[6]
• Sepsis, severe infections, heart failure, or liver disease. ^[7]
• Older age or acute illnesses that can impair kidney function. ^[6]
• In real-world reports, most lactic acidosis cases involved other medical problems (often acute kidney injury) or inappropriate use. ^{[7] [6]}

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How common is it

• Lactic acidosis with metformin is very rare when the drug is used correctly, but it is serious when it happens. ^[8]
• Reviews show few cases relative to how widely metformin is used, and many cases had other clear reasons for lactic acidosis (like sepsis or renal failure). ^[8]
• Risk is considered low with appropriate prescribing and monitoring. ^[9]

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What to do if you have muscle pain

If it’s mild and you feel otherwise well

• Consider other causes (exercise, new medications like statins), stay hydrated, and monitor for any additional warning signs.
• If muscle pain persists or worsens, contact your clinician to discuss whether metformin or another cause is responsible.

If muscle pain is “unusual” and you also have red-flag symptoms

• Stop metformin and seek urgent evaluation immediately. ^[1]
• Emergency care is needed because lactic acidosis must be treated in a hospital, and prompt hemodialysis may be recommended. ^{[2] [3] [5]}

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Practical prevention tips

• Know the symptoms above and act quickly if they occur. ^[1]
• Hold metformin during acute illnesses that may dehydrate you (severe vomiting/diarrhea) and contact your clinician for guidance. ^[6]
• Have kidney function checked regularly and before dose changes; impaired kidneys increase risk. ^{[7] [6]}
• Inform your care team about new medications or conditions that could affect kidneys, heart, or liver. ^[7]

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At-a-glance: When to worry

Situation	Likely action	Why it matters
Mild muscle soreness after exercise, no other symptoms	Monitor; stay hydrated; discuss if persistent	Common and usually benign, not typical for lactic acidosis
Unusual muscle pain + severe fatigue or shortness of breath	Stop metformin and seek urgent care	Cluster of warning signs suggests possible lactic acidosis. [1]
Unusual muscle pain + stomach upset (nausea, vomiting, diarrhea) + feeling cold/dizzy	Stop metformin and seek urgent care	Multiple hallmark symptoms; emergency evaluation needed. [1] [2]
Any slow/irregular heartbeat with the above symptoms	Emergency care now	High‑risk presentation; hospital treatment may include hemodialysis. [1] [3] [5]

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Bottom line

• Metformin can be associated with unusual muscle pain, and this symptom can be an early warning sign of lactic acidosis especially when it appears with breathing trouble, severe fatigue, stomach symptoms, feeling cold, dizziness, or a slow/irregular heartbeat. ^[1]
• Although lactic acidosis is rare with proper use, it is serious and needs urgent care; stop metformin and seek immediate medical attention if these signs occur. ^{[2] [8] [3] [5]}