Naproxen 500 mg is a prescription-strength anti-inflammatory drug, and its most common side effects involve the stomach: pain, heartburn, nausea, and gas. These digestive symptoms are the ones most people notice first, but naproxen can also affect your heart, kidneys, and skin, especially with longer use. Here’s what to expect and what to watch for.
Common Side Effects
The side effects most people experience with naproxen 500 mg are mild and centered on the digestive system. Stomach pain, bloating, gas, heartburn, and constipation are all typical. You may also notice headaches, dizziness, drowsiness, or lightheadedness, particularly in the first few days of use.
Some less obvious but still common effects include excessive thirst, difficulty sleeping, ringing in the ears, and a burning or tingling sensation in your arms or legs. These tend to be manageable for most people and often improve as your body adjusts. If any of them persist or get worse over time, that’s worth a conversation with your doctor rather than something to push through.
Stomach and Digestive Risks
Gastrointestinal damage is the most well-documented serious risk of naproxen. The FDA places a black box warning on naproxen for this reason: it can cause bleeding, ulceration, and even perforation of the stomach or intestines. These events can happen at any point during use and sometimes occur without any warning symptoms beforehand.
The numbers are striking. In clinical trials where patients took naproxen 500 mg twice daily for up to six months, roughly 28% developed ulcers detectable by endoscopy. Among long-term users of NSAIDs broadly, 15% to 30% develop endoscopic ulcers, and 2% to 4% of those ulcers lead to serious complications like bleeding or perforation. Elderly patients and anyone with a history of peptic ulcer disease face the highest risk.
Your risk also goes up if you take naproxen alongside low-dose aspirin, corticosteroids, or SSRI antidepressants. Taking naproxen with food or milk can reduce everyday stomach irritation, but it doesn’t eliminate the deeper risk of ulcer formation with prolonged use.
Heart and Stroke Risk
All NSAIDs carry an FDA black box warning for increased risk of heart attack and stroke. This risk can appear early in treatment and tends to grow the longer you take the medication. Naproxen is contraindicated after coronary artery bypass graft surgery.
That said, naproxen consistently shows a better cardiovascular safety profile than other common NSAIDs. In a large study of patients with serious coronary heart disease, naproxen users had the lowest rates of heart attack and cardiovascular death compared to nonusers and users of other NSAIDs. Diclofenac users had a 44% higher risk of serious coronary events compared to naproxen users, and ibuprofen users had a 25% higher risk of serious cardiovascular events or death. This relative safety advantage is one reason doctors sometimes prefer naproxen for patients who need long-term anti-inflammatory treatment.
Effects on the Kidneys
Naproxen reduces the production of certain chemicals (prostaglandins) that help maintain blood flow to your kidneys. Under normal circumstances, your kidneys handle this fine. But when your body is already under stress, such as during dehydration, blood loss, or if you have reduced kidney function, naproxen can tip the balance and cause a sudden drop in kidney performance.
The risk of acute kidney injury is most pronounced in people with mild to moderate chronic kidney disease, particularly if they’re also taking blood pressure medications that affect the same system (like ACE inhibitors) or diuretics. Signs to watch for include noticeably decreased urination, swelling in your ankles or feet, unexplained weight gain, and cloudy or bloody urine.
Skin and Allergic Reactions
Naproxen can trigger allergic reactions ranging from mild to severe. Common skin-related effects include rashes, itching, and hives. More concerning reactions involve swelling of the face, lips, tongue, or throat, difficulty breathing or swallowing, and blistering or reddening of the skin. These warrant immediate medical attention, as they can signal a serious allergic response.
Short-Term vs. Long-Term Use
How long you take naproxen significantly changes your risk profile. A few days of use for a headache, muscle strain, or menstrual cramps carries relatively low risk for most people. The common side effects (stomach discomfort, headache, mild dizziness) are what you’re most likely to encounter with occasional use.
With weeks or months of daily use, the picture shifts. Ulcer risk climbs steadily, cardiovascular risk accumulates, and the potential for kidney problems increases. The FDA warning specifically notes that cardiovascular risk “may increase with duration of use.” This is why doctors generally recommend using the lowest effective dose for the shortest time needed.
Drug Interactions to Know About
Naproxen interacts with several commonly prescribed medications. If you take lithium for bipolar disorder, adding naproxen can push lithium levels dangerously high by reducing how quickly your kidneys clear it. In one documented case, adding an NSAID to a patient’s lithium regimen triggered fatal toxicity. Blood thinners are another major concern: naproxen increases the risk of bleeding on its own, and combining it with anticoagulants amplifies that risk substantially.
SSRIs, a widely used class of antidepressants, also raise the chance of gastrointestinal bleeding when combined with naproxen. The same is true for corticosteroids and low-dose aspirin. If you’re taking any of these medications, that combination deserves specific attention from your prescriber.
Higher Risk for Older Adults
People over 65 are more vulnerable to nearly every serious side effect of naproxen. Their stomachs are more prone to ulceration, their kidneys are more sensitive to blood flow changes, and they’re more likely to be taking other medications that interact with naproxen. Confusion, which can be mistaken for age-related cognitive changes, is also a potential side effect worth being aware of in this group.
Signs of Overdose
Taking too much naproxen can cause severe symptoms including agitation, confusion, blurred vision, seizures, severe stomach pain with possible internal bleeding, slow or labored breathing, and in extreme cases, coma. Even moderate overdoses may produce intense drowsiness, severe headache, nausea, vomiting, and ringing in the ears. If you suspect an overdose, this is a situation that requires emergency care, not a wait-and-see approach.