Supplements and Furosemide.
Furosemide, sold under the brand name Lasix, is a loop diuretic: it inhibits sodium and chloride reabsorption in the loop of Henle, producing a strong diuresis.
Furosemide is the most prescribed loop diuretic in England. It is used for fluid overload in heart failure, chronic kidney disease, and resistant hypertension. It inhibits the Na-K-2Cl cotransporter in the loop of Henle, driving a strong sodium and water diuresis. The metabolic consequences sit at the centre of the supplement question. Furosemide depletes potassium and magnesium. Chronic use depletes thiamine (B1) too. The thiamine signal in heart failure patients on chronic loop diuretic was first reported in the late 1990s and confirmed in multiple cohorts since. Some clinicians prescribe oral thiamine routinely. Potassium and magnesium loss can drive arrhythmia, cramping, and fatigue, and supplementation is often co-prescribed. Calcium and zinc absorption are also affected, though less prominently. The interaction with NSAIDs (ibuprofen and naproxen) is documented. They blunt furosemide's diuretic effect and add to renal stress in patients with established kidney impairment.
Below are the 4 documented pairs we have explicitly assessed against Furosemide in the Distil database: 4 amber. The pairs cluster around 2 mechanisms: Additive blood-pressure lowering and Renal magnesium wasting (drug-induced). Every call is cited to either a clinical reference (PMID) or the British National Formulary. Anything not on this list is either still to be assessed or beyond our database scope. The checker beneath surfaces assessments by supplement, and the missing-item form at the bottom of the page routes any uncatalogued supplement into our next curation pass.
Documented interactions
Additive blood-pressure lowering
Taken at night, melatonin can modestly lower blood pressure during sleep. Combined with a blood-pressure or fluid medicine like furosemide this may add up to a slightly larger drop than the medicine alone. This is usually mild, but if you notice dizziness or lightheadedness, check your blood pressure and mention it to your prescriber.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Renal magnesium wasting (drug-induced)
Furosemide makes the kidneys pass out more magnesium in the urine, so people on it long term often run low on magnesium. This works the opposite way to most interactions: the medicine lowers your magnesium rather than the supplement affecting the medicine, so taking magnesium is generally a supportive response rather than a hazard. If you take furosemide long term, especially for heart failure, it is worth asking your GP for a magnesium blood test and letting them know you supplement, since low magnesium can affect heart rhythm.
Furosemide makes the kidneys pass out more magnesium in the urine, so people on it long term often run low on magnesium. This works the opposite way to most interactions: the medicine lowers your magnesium rather than the supplement affecting the medicine, so taking magnesium is generally a supportive response rather than a hazard. If you take furosemide long term, especially for heart failure, it is worth asking your GP for a magnesium blood test and letting them know you supplement, since low magnesium can affect heart rhythm.
Furosemide makes the kidneys pass out more magnesium in the urine, so people on it long term often run low on magnesium. This works the opposite way to most interactions: the medicine lowers your magnesium rather than the supplement affecting the medicine, so taking magnesium is generally a supportive response rather than a hazard. If you take furosemide long term, especially for heart failure, it is worth asking your GP for a magnesium blood test and letting them know you supplement, since low magnesium can affect heart rhythm.
What this list does not say. Pairs not flagged here are not implicitly safe. They are either not yet in our database, or fall outside our inclusion scope (food-supplement interactions only; for drug-drug interactions, the BNF is authoritative). Use the checker below to surface any supplement, and submit a missing item if you take something we have not catalogued.
How we grade severity, choose what's in scope, and what we exclude.
Every call on this page is reasoned. We publish the full rubric for severity tiers, the medication inclusion logic, the evidence grades we accept, and what we deliberately leave out. About three thousand words. Worth reading once if you use this tool more than occasionally.
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