Naproxen is one of the most widely used over-the-counter pain relievers, but it carries a real list of side effects that range from mild stomach discomfort to serious cardiovascular and gastrointestinal events. The FDA requires a boxed warning (the most serious type) on naproxen for both heart-related and stomach-related risks. Understanding these side effects helps you weigh the benefits against the risks, especially if you take it regularly.
Common, Everyday Side Effects
The side effects most people notice first are digestive. Heartburn, nausea, stomach pain, and a general feeling of indigestion are the most frequently reported complaints. These tend to show up within the first few days of use and often persist as long as you keep taking the drug. Headache, dizziness, and drowsiness round out the common side effects. Some people also experience mild swelling in the hands, feet, or ankles from fluid retention.
These reactions are usually more annoying than dangerous, but they’re not trivial. Persistent nausea or stomach pain can affect your appetite and quality of life. Taking naproxen with food or a full glass of water can reduce stomach irritation for some people, though it won’t eliminate the risk entirely.
Stomach Bleeding and Ulcers
This is where naproxen’s risks become serious. The drug works by blocking enzymes that produce inflammation, but those same enzymes also help maintain the protective lining of your stomach. When that lining weakens, stomach acid can damage the tissue directly, leading to ulcers, bleeding, or in rare cases, a hole in the stomach wall (perforation).
Among people who take naproxen or similar anti-inflammatory drugs regularly, 2 to 4% develop a symptomatic peptic ulcer each year, and 1 to 3% experience a serious upper GI complication like significant bleeding. That’s a three- to fivefold increase compared to people who don’t use these drugs. The FDA’s boxed warning states these events “can occur at any time during use and without warning symptoms,” meaning you won’t necessarily feel an ulcer forming before it becomes an emergency.
Your risk is higher if you’re over 65, have a history of stomach ulcers, drink alcohol regularly, or take blood thinners at the same time. Black or tarry stools, vomiting blood, or sudden severe stomach pain are signs of GI bleeding that need immediate medical attention.
Heart Attack and Stroke Risk
Naproxen, like all anti-inflammatory painkillers in its class, increases the risk of heart attack and stroke. The FDA’s boxed warning is direct: this risk “may occur early in treatment and may increase with duration of use.” You don’t need to take it for months before the danger kicks in.
That said, naproxen has generally fared better in cardiovascular comparisons than some of its relatives. In the large PRECISION trial, which followed thousands of arthritis patients, the rate of cardiovascular death, heart attack, or stroke was 2.5% with naproxen, compared to 2.7% with ibuprofen and 2.3% with celecoxib. The differences were small, and all three drugs were considered broadly comparable in cardiovascular safety. Still, any increase matters if you already have heart disease, high blood pressure, or other cardiovascular risk factors. Naproxen is completely off-limits if you’re recovering from coronary artery bypass surgery.
Kidney Damage
Your kidneys rely on the same inflammation-related chemical signals that naproxen suppresses. Blocking those signals reduces blood flow to the kidneys, which can impair their ability to filter waste. For most healthy people taking naproxen occasionally, this isn’t a meaningful concern. But for anyone with existing kidney problems, it can tip the balance toward real damage.
The National Kidney Foundation recommends that people with chronic kidney disease avoid naproxen and similar drugs entirely if their kidney filtration rate (eGFR) is below 60, a number your doctor can check with a simple blood test. Even without prior kidney issues, long-term daily use of naproxen can gradually reduce kidney function, particularly in older adults or people who are dehydrated.
Signs of kidney trouble include noticeably decreased urination, swelling in the legs or feet, unexplained fatigue, and confusion. These symptoms develop gradually, so they’re easy to dismiss.
Blood Pressure and Fluid Retention
Naproxen can raise blood pressure by causing your body to hold onto sodium and water. If you’re already managing high blood pressure with medication, naproxen can partially counteract what those drugs are doing. This is one of the most overlooked interactions: people take their blood pressure medication faithfully, then grab naproxen for a sore back, and their readings creep up without an obvious explanation.
The fluid retention can also worsen heart failure in people who are already at risk. Swollen ankles, sudden weight gain over a few days, and shortness of breath are warning signs that your body is retaining too much fluid.
Dangerous Drug Interactions
Naproxen interacts with several common medications in ways that multiply its risks:
- Blood thinners: Naproxen reduces your blood’s ability to clot by interfering with platelet function. Combined with anticoagulant medications, this can significantly raise the risk of serious bleeding. Research published by the American Heart Association found that naproxen increases blood levels of certain anticoagulants, compounding the bleeding risk beyond what either drug would cause alone.
- Blood pressure medications: As noted above, naproxen can blunt the effectiveness of drugs used to treat high blood pressure, including ACE inhibitors, diuretics, and similar medications.
- Other anti-inflammatory painkillers: Taking naproxen alongside ibuprofen or aspirin doesn’t double the pain relief, but it does stack the stomach and kidney risks. Low-dose aspirin for heart protection is a particular concern, because naproxen can interfere with aspirin’s protective effect on platelets.
- Certain antidepressants: SSRIs, one of the most commonly prescribed types of antidepressants, also affect platelet function. The combination with naproxen increases bleeding risk more than either drug alone.
Risks for Older Adults
People over 65 face a higher incidence of nearly every serious naproxen side effect. The stomach lining becomes more vulnerable with age. Kidney function naturally declines. Cardiovascular risk factors accumulate. And older adults are more likely to be taking multiple medications that interact with naproxen.
The FDA’s labeling specifically calls out elderly patients as being at greater risk for serious gastrointestinal events. This doesn’t mean naproxen is never appropriate for older adults, but the threshold for concern is lower, and shorter courses at the lowest effective dose become more important. Prescription maximum doses go up to 1,500 mg per day for conditions like rheumatoid arthritis, but many older adults should stay well below that ceiling.
Less Common but Notable Effects
Beyond the major risks, naproxen can cause a range of less frequent side effects. Some people develop rashes, ringing in the ears, or blurred vision. Liver enzyme elevations occur occasionally, though serious liver injury is rare. Allergic reactions, including facial swelling and difficulty breathing, are uncommon but possible, particularly in people who are sensitive to aspirin or other anti-inflammatory drugs.
Prolonged use has also been linked to anemia, because chronic low-level bleeding in the digestive tract can slowly deplete your iron stores without producing obvious symptoms. If you take naproxen regularly and feel increasingly tired or short of breath during normal activities, that connection is worth exploring with a blood test.