Is Thiamine (B1) Safe with Furosemide?
Free · No account · based on published sources including NIH ODS, FDA drug labels, and peer-reviewed literature
Patients on long-term furosemide, especially those with heart failure or poor nutritional intake, should discuss thiamine supplementation with their provider. A daily B-complex or thiamine 100mg/day is often recommended in clinical practice.
Why this interaction occurs
Furosemide increases urinary thiamine excretion. Chronic loop diuretic use has been associated with clinically significant thiamine deficiency, which can worsen cardiac function (high-output heart failure, Wernicke's encephalopathy). Studies in heart failure patients on furosemide show measurable reductions in thiamine status compared to controls.
Evidence
Evidence level: moderate.
Reported safety data
The FDA’s adverse event reporting system (FAERS) has received 274,011 reports mentioning Furosemide. This reflects reported cases involving the medication in general — not confirmed causation, and not specific to the Furosemide + supplement combination on this page.
FAERS reports are voluntary and cannot prove that a drug caused an event. Do not use report counts to assess the safety of this specific drug-supplement pair.
Frequently asked questions
Related interactions
All Thiamine (B1) interactions → · All Furosemide interactions →
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Educational only — not medical advice.
Always confirm with your doctor or pharmacist.