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Metformin side effects — what to expect and when to call
Metformin is highly effective and generally well-tolerated. Here's how to manage side effects and recognise serious reactions.
4 min read · Last reviewed 2026-05-03
Common side effects
Gastrointestinal effects are most common, especially when starting or increasing the dose.
- • Nausea and diarrhea
- • Metallic taste
- • Reduced appetite
How to minimise them
Most GI side effects settle within 1–2 weeks.
- • Take with meals
- • Start with a low dose and titrate slowly
- • Consider extended-release formulation
When to call a clinician
Rarely, metformin can cause lactic acidosis — usually in the context of kidney impairment, dehydration, or acute illness.
- • Severe vomiting or diarrhea
- • Deep, rapid breathing
- • Unusual muscle pain or weakness
Key takeaways
- ✓ Most side effects improve with time and dose adjustment.
- ✓ Hold metformin during acute illness with dehydration.
- ✓ Annual kidney function checks are recommended.
When to seek care
- • Severe or persistent GI symptoms
- • Any sign of lactic acidosis
Questions about a medication?
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FAQs
Does metformin cause low blood sugar?
On its own, very rarely. The risk increases when combined with insulin or sulfonylureas.
Medical oversight: Content aligned with NICE, WHO and CDC references. Educational, not a substitute for personal medical advice.