No. Furosemide and lithium should not be taken together. According to FDA-derived drug interaction data, this combination is contraindicated—meaning the drugs should be avoided together because furosemide reduces the kidney's ability to clear lithium from the body, creating a high risk of lithium toxicity. If you are currently taking both medications, or if a healthcare provider has suggested this combination, you must discuss this interaction with a pharmacist or physician before filling or taking any dose.
The interaction record controlling this article comes from FDA drug labeling data compiled by the National Library of Medicine. Here is what the authoritative source documents:
A "contraindicated" rating is one of the highest levels of interaction severity in clinical pharmacy. It means the combination carries serious risk and should generally be avoided unless there is no suitable alternative and a prescriber has explicitly weighed the benefits against the documented dangers. Unlike a "major" interaction (which may be managed with dose adjustment or close monitoring), contraindicated combinations are typically not managed through standard modifications—they are avoided.
Furosemide is a loop diuretic, a powerful water pill used to treat high blood pressure, heart failure, kidney disease, and other conditions characterized by fluid overload. It works by blocking sodium and chloride reabsorption in the thick ascending limb of the loop of Henle, a key filtering structure in the kidney. This action causes the kidneys to excrete much more sodium and water than they normally would—which is why it is so effective for reducing fluid buildup in the body.
Lithium is a mood-stabilizing medication used primarily to treat bipolar disorder and sometimes depression. Unlike most psychiatric medications, lithium is not metabolized (broken down) by the liver. Instead, the kidneys filter it almost unchanged from the blood into the urine. This means that lithium levels in the blood depend almost entirely on how efficiently the kidneys are clearing it.
The therapeutic range for lithium is narrow—the dose that helps is not far below the dose that harms. Lithium toxicity can cause tremor, confusion, nausea, diarrhea, irregular heartbeat, and in severe cases, kidney damage and seizures. Because the margin between therapeutic and toxic levels is so small, anything that slows lithium clearance can quickly push blood levels into the dangerous zone.
The source record specifies that furosemide reduces lithium's renal clearance. In plain language, this means furosemide interferes with the kidney's ability to filter lithium out of the bloodstream and into the urine. The result is that lithium accumulates in the body and in the blood.
How does a diuretic reduce lithium clearance? General renal physiology offers important background: loop diuretics like furosemide cause sodium depletion and reduce the volume of fluid in the bloodstream. The kidneys sense this reduced blood volume and activate compensatory mechanisms—they try to hold onto sodium and water to preserve circulation. When the kidneys are reabsorbing sodium more aggressively, they also reabsorb lithium (which follows sodium through the proximal tubule of the nephron). This increased reabsorption of lithium means less lithium is excreted in the urine, leading to higher blood levels. This is general pharmacology well established in clinical nephrology and psychiatry textbooks; the source record confirms that this mechanism applies to the furosemide–lithium pair.
In clinical pharmacy, "contraindicated" interactions typically mean the risk is not readily managed by standard interventions (closer monitoring, dose reduction, timing adjustments). Unlike some major interactions where a smaller dose of one drug or more frequent blood testing can mitigate risk, the structural problem here—that furosemide reduces lithium clearance—is difficult to overcome. Reducing the lithium dose might lower toxicity risk, but furosemide's effect on kidney sodium handling and fluid balance is not easily separated from its diuretic benefit. For this reason, the source documentation recommends avoiding the combination entirely.
Anyone currently taking both furosemide and lithium, or for whom both drugs have been recommended, should immediately discuss the interaction with a pharmacist or prescriber. This includes patients with:
Patients with reduced kidney function are at even higher risk, because baseline renal clearance of lithium is already compromised; adding furosemide on top of existing renal impairment makes lithium toxicity more likely and more severe.
The very young, the elderly, and patients taking other medications that affect kidney function or sodium balance should also discuss this combination carefully with a healthcare provider, as these populations are often more vulnerable to both the therapeutic and toxic effects of lithium.
Imagine a 58-year-old patient who has taken lithium for 20 years to manage bipolar disorder, with stable blood levels and good therapeutic response. The patient develops heart failure (weakening of the heart muscle) and a cardiologist prescribes furosemide to reduce fluid in the lungs and legs. Within days to weeks, the patient begins to feel confused, nauseated, and develops fine hand tremors. Blood work shows that lithium levels have risen from 0.8 mEq/L (therapeutic) to 1.5 mEq/L (toxic). This change did not occur because the patient took too much lithium or because kidney disease suddenly worsened—it occurred because furosemide reduced the kidneys' ability to clear lithium. This is a direct, documented consequence of the interaction described in the source record.
A patient taking lithium for mood stabilization visits their primary care doctor for high blood pressure. The doctor, noting swollen ankles and mild fluid retention, prescribes furosemide. If the patient or the doctor is not aware of the interaction, the patient might not have lithium levels checked. Over several weeks, lithium accumulates. The patient develops polyuria (excessive urination), polydipsia (excessive thirst), and worsening confusion—symptoms that can be mistaken for worsening mental illness rather than drug toxicity. Lithium toxicity damages the kidneys themselves, worsening the problem further. This scenario underscores why awareness of the interaction is critical: the harm can be subtle and easily misattributed.
Both scenarios illustrate the mechanism documented in the source record: furosemide reduces lithium clearance, and the result is elevated lithium levels and toxicity risk.
If you are taking lithium and furosemide has been recommended to you, or if you are taking furosemide and lithium has been recommended, bring this interaction to your healthcare provider's attention. Here are questions that may help structure that conversation:
Do not stop, skip, or change your medication on your own based on this article. Medication decisions must be made in consultation with your prescriber and pharmacist, who can weigh your individual health status, alternative options, and the severity of your conditions.
The interaction data in this article comes from FDA drug labeling as compiled and distributed by the National Library of Medicine through its RxNorm and drug interaction databases:
For more information on lithium toxicity, renal effects, and management, consult your pharmacist, physician, or psychiatrist. Clinical guidelines on lithium use in bipolar disorder are published by major psychiatric and medical societies, including the American Psychiatric Association and the National Institute of Mental Health.
If you are taking any combination of medications, use checkdruginteractions.com to identify potential interactions before they cause harm. Enter your full medication list—including over-the-counter drugs, supplements, and herbal products—and review the results with a pharmacist or physician. The goal is to catch dangerous combinations like furosemide and lithium before they result in adverse effects. Your pharmacist and doctor are your partners in safe medication use; do not hesitate to ask them about any interaction you discover or any concern you have about your medications.
CDI checks every pair across up to 20 drugs — backed by FDA and NIH data.
Drug interaction data sourced from U.S. FDA drug labeling via openFDA and the U.S. National Library of Medicine (NLM), National Institutes of Health. For informational purposes only. Always consult your pharmacist or physician before making any medication decisions.
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