Biguanide

Who should not take metformin?

Q: How common are metformin side effects?

GI side effects are by far the most common with metformin: diarrhea (up to 53% initially), nausea (up to 26%), vomiting, bloating, and a metallic taste. The good news is these typically improve significantly within 2-4 weeks, especially if you start at a low dose and take it with food. Extended-rele

Q: Are there natural alternatives to metformin?

Lifestyle interventions are actually the first-line recommendation for type 2 diabetes prevention and early management. The Diabetes Prevention Program (DPP) trial showed that intensive lifestyle changes (diet + 150 min/week exercise) reduced diabetes risk by 58%, compared to 31% for metformin alone

Direct Answer

Metformin is contraindicated in people with severe kidney disease (eGFR below 30), as the kidneys clear metformin and impaired clearance raises lactic acidosis risk. It should be temporarily stopped before procedures involving iodinated contrast dye and during acute illness with dehydration. People with severe liver disease, uncontrolled heart failure, or a history of lactic acidosis should not take it. Heavy alcohol use is a relative contraindication because alcohol independently raises lactate levels. For everyone else, metformin has one of the best safety profiles of any diabetes medication, with over 60 years of clinical use.

Based on published clinical trial data and FDA prescribing information. This is not medical advice — always consult your healthcare provider.

Supporting Evidence

Side Effects

Nausea25%

Diarrhea28%

Stomach upset / cramping20%

Vomiting7%

Metallic taste in mouth15%

Serious (rare)

Lactic acidosis (rare but potentially fatal)
Vitamin B12 deficiency (long-term)
Hypoglycemia (when combined with insulin/sulfonylureas)

Drug Interactions

MAJOR

Contrast dye— Stop 48h before imaging - kidney failure risk

MAJOR

Alcohol— Lactic acidosis (rare but serious)

MOD

Topiramate— Lactic acidosis risk

MOD

Carbonic anhydrase inhibitors— Lactic acidosis risk

Clinical Trials

A1C -1.5%, weight neutral, possible longevity benefits

DPP (NIH)MILES (Metformin Longevity)

Funding transparency: UKPDS: UK government funded. DPP: NIH funded. Most major metformin trials are government or non-profit funded, unusual for diabetes drugs. See full funding details

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