Nitrofurantoin changes your urine color because the drug is rapidly filtered out through your kidneys, and the drug itself has a brown pigment that tints your urine on the way out. The color shift typically ranges from rust-yellow to brown, and it’s a normal, harmless side effect that doesn’t mean anything is wrong with your kidneys or bladder.
What Causes the Color Change
Nitrofurantoin is an antibiotic used to treat urinary tract infections. Unlike many drugs that are broken down primarily by the liver, nitrofurantoin is rapidly excreted through the urine in high concentrations. That’s actually the whole point of the drug: it concentrates in the urinary tract, which is where the infection lives. As a side effect of all that drug passing through, the natural pigment of nitrofurantoin tints your urine.
The FDA prescribing information states it plainly: “Nitrofurantoin is rapidly excreted in urine, to which it may impart a brown color.” The color you see isn’t a metabolic byproduct or a sign of kidney stress. It’s the drug itself, dissolved in your urine.
What Color to Expect
Most people notice their urine turns somewhere in the range of rust-yellow to brown. The exact shade varies from person to person and can look different depending on how hydrated you are. If you’re drinking plenty of fluids, your urine will be more dilute and the tint lighter. If you’re less hydrated, the color can look noticeably darker, closer to a deep brown.
This color change can start with your first dose and continues throughout the course of treatment. It’s not something that builds up over time or signals that the drug is accumulating to dangerous levels.
When the Color Returns to Normal
Your urine will return to its usual color once you stop taking nitrofurantoin. Because the drug clears through the kidneys quickly, most people notice the color normalizing within a day or so of finishing their prescription. The NHS confirms this directly: “Your pee will return to its usual colour once you stop taking nitrofurantoin.”
Color Changes That Aren’t Normal
The rust-yellow to brown tint from nitrofurantoin is expected and harmless. But certain color changes alongside other symptoms can signal a real problem. If you notice dark urine combined with pale-colored stool, or if the whites of your eyes or your skin develop a yellowish tint, that pattern can indicate a liver or gallbladder issue rather than the normal drug pigment effect. On darker skin tones, yellowing may be easier to spot in the whites of the eyes than on the skin itself.
The key distinction: brown-tinted urine on its own while taking nitrofurantoin is the drug doing what it does. Brown urine paired with pale stool, yellowing eyes, or yellowing skin is a different situation entirely and warrants prompt medical attention.
Staining Beyond Urine
Because nitrofurantoin’s pigment is concentrated in urine, it can stain underwear or clothing if urine comes into contact with fabric. Some people also notice that the drug can temporarily discolor contact lenses if you touch them after handling the medication without washing your hands. Using a panty liner during treatment and washing hands before touching contacts or light-colored fabrics can save you minor hassle.
The color change doesn’t affect urine in any way that matters for your health, but it can interfere with certain urine tests. If you’re having a urinalysis done for another reason while taking nitrofurantoin, let the lab know you’re on the medication so they can account for the discoloration when interpreting results.