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What are the most common side effects of taking metformin?
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Common side effects may include nausea, vomiting, diarrhea, stomach pain, bloating, gas, constipation, headache, and rash. Other rare but more serious side effects can include lactic acidosis (a buildup of lactic acid in the blood), kidney problems, low blood sugar levels, and liver damage. If you experience any of these symptoms while taking metformin, contact your doctor immediately.