Nitrofurantoin, a widely prescribed antibiotic for urinary tract infections, causes nausea and stomach upset in a significant number of people who take it. Most side effects are mild and go away once you finish the course, but this drug can also cause rare, serious reactions involving the lungs, liver, and nerves, especially with long-term use.
Stomach Problems and Nausea
The most common complaint with nitrofurantoin is nausea, sometimes accompanied by vomiting, loss of appetite, or diarrhea. These symptoms are usually mild and tend to improve over the course of treatment. Taking the medication with food or a glass of milk reduces stomach irritation and also helps your body absorb the drug more effectively, so this is worth doing every time you take a dose.
Headaches and dizziness can also occur during treatment. These are generally short-lived and resolve once you stop the medication.
Dark Urine Is Normal
Your urine may turn dark yellow or brownish while you’re taking nitrofurantoin. This is completely harmless and happens because of how the drug is processed and excreted by your kidneys. Your urine will return to its normal color after you finish the course. It’s worth knowing about this in advance so it doesn’t catch you off guard.
Lung Reactions
Nitrofurantoin can cause two distinct types of lung injury, depending on how long you’ve been taking it. The acute form typically appears around nine days into a short course of therapy and can cause sudden shortness of breath, chest pain, cough, and fever. These symptoms can look a lot like pneumonia, which sometimes leads to a delayed diagnosis.
The chronic form develops after months or years of continuous use, most often in people taking nitrofurantoin as a long-term preventive measure against recurrent UTIs. Symptoms come on gradually: a persistent dry cough, increasing breathlessness during everyday activities, and fatigue. The chronic form is particularly concerning because it can cause lasting lung damage if not caught early. If you’re on long-term nitrofurantoin and notice a new cough or worsening shortness of breath, that warrants prompt medical attention.
Nerve Damage
Nitrofurantoin can cause peripheral neuropathy, which means damage to the nerves in your hands, arms, legs, or feet. You might notice numbness, tingling, burning pain, or weakness in these areas. This side effect is more common with prolonged use, but it can happen during shorter courses too.
The critical thing to know is that this nerve damage can be severe and, in some cases, irreversible. If you start feeling any unusual tingling or numbness in your extremities while taking nitrofurantoin, report it right away so the medication can be stopped before permanent damage occurs. People with reduced kidney function face a higher risk of neuropathy because their bodies clear the drug more slowly, allowing it to build up in the blood.
Liver Injury
Nitrofurantoin can cause liver damage, and this can happen even with short courses of treatment. Warning signs include yellowing of the skin or eyes, pain in the upper right side of your abdomen, unusually dark urine (darker than the expected brownish tinge from the drug itself), pale or grey stools, itching, and joint pain or swelling.
People who have experienced liver problems from nitrofurantoin in the past should never take it again. Those with existing liver conditions can sometimes use it, but need closer monitoring. For anyone on long-term therapy, periodic liver function checks are recommended to catch problems before they become serious.
Blood Disorders and G6PD Deficiency
Nitrofurantoin can trigger a condition called hemolytic anemia, where red blood cells break down faster than your body can replace them. This risk is especially relevant for people with G6PD deficiency, a genetic condition that affects how red blood cells handle oxidative stress. G6PD deficiency is particularly common in people of African, Mediterranean, and Southeast Asian descent.
Clinical guidelines classify nitrofurantoin as a medium-risk drug for people with G6PD deficiency. If you have G6PD deficiency without chronic anemia, the drug can be used cautiously with close monitoring for signs of anemia (fatigue, paleness, rapid heartbeat, dark urine). If you have G6PD deficiency with an existing chronic form of hemolytic anemia, nitrofurantoin should be avoided entirely.
Kidney Function Matters
Your kidneys play a central role in how nitrofurantoin works. The drug concentrates in urine to fight bacteria in the urinary tract, so when kidney function is impaired, two things go wrong: the drug doesn’t reach high enough levels in urine to be effective, and it accumulates in the blood, raising the risk of side effects like nerve damage.
Current guidelines set a clear threshold. Nitrofurantoin is not recommended for people whose kidney filtration rate (eGFR) falls below 45. In a narrow range of 30 to 44, a short course of 3 to 7 days may be considered, but only when other antibiotics aren’t suitable and the infection involves drug-resistant bacteria. Below 30, the drug is simply too risky and too ineffective to use.
Risks in Late Pregnancy
Nitrofurantoin is generally considered safe in the first and second trimesters of pregnancy, but it’s avoided during the third trimester and especially during labor and delivery. The concern is that a newborn’s red blood cells lack the mature enzyme systems needed to handle the oxidative stress the drug creates. This creates a theoretical risk of hemolytic anemia in the baby, where red blood cells break down in the first days of life. For this reason, other antibiotics are typically preferred for UTIs late in pregnancy.
How to Reduce Side Effects
The simplest and most effective strategy is to always take nitrofurantoin with food. This significantly cuts down on nausea and stomach discomfort while improving absorption. If you’re prescribed the macrocrystalline form (the most common version), it’s specifically designed for slower release to reduce GI symptoms compared to older formulations.
Stay alert for symptoms that go beyond ordinary stomach upset. Tingling or numbness in your hands or feet, unexplained shortness of breath, a persistent cough, yellowing skin, or unusual fatigue are all signals that something more serious may be developing. Most people complete their course of nitrofurantoin without any problems beyond mild nausea, but knowing what to watch for makes a real difference in catching the rare serious reactions early enough to prevent lasting harm.