Naproxen 500 mg is a prescription-strength nonsteroidal anti-inflammatory drug (NSAID) used to treat pain, inflammation, and stiffness caused by conditions like arthritis, gout, menstrual cramps, tendinitis, and headaches including migraine. It works by blocking the enzymes responsible for producing prostaglandins, the chemical messengers that drive pain and swelling. Because a single dose lasts considerably longer than most over-the-counter pain relievers, naproxen 500 mg is often taken just twice a day, making it a convenient option for conditions that need steady, all-day relief.
How Naproxen Works
Your body produces prostaglandins through an enzyme called cyclooxygenase, which comes in two main forms (COX-1 and COX-2). When tissue is injured or inflamed, COX-2 ramps up prostaglandin production, leading to swelling, pain, and fever. Naproxen blocks both COX-1 and COX-2, which is why it reduces inflammation effectively but also why it carries certain side effects. Research into naproxen’s molecular structure has shown that its chemical scaffold fits snugly into the COX enzyme’s active site, and even small changes to the molecule’s shape sharply reduce its ability to block the enzyme.1Europe PMC. Molecular basis for cyclooxygenase inhibition by the non-steroidal anti-inflammatory drug naproxen
Blocking prostaglandin production is what makes naproxen useful for so many different types of pain. Whether the prostaglandins are being generated by an arthritic joint, a gout flare, or the lining of the uterus during menstruation, the same underlying mechanism is at work. That broad applicability is part of why naproxen is one of the most widely used NSAIDs worldwide, available both over the counter at lower doses and by prescription at 500 mg.
Arthritis and Joint Pain
Naproxen 500 mg is one of the most commonly prescribed medications for both osteoarthritis and rheumatoid arthritis. In osteoarthritis, inflammation in the synovial fluid surrounding the joint contributes to pain and stiffness. Lab research on human osteoarthritis tissue has shown that naproxen reduces the activity of key inflammatory pathways in joint fluid cells. Specifically, it cut the production of several inflammatory signaling molecules made by monocytes and macrophages in osteoarthritic synovial fluid.2PubMed Central. Naproxen with or without an antiemetic for acute migraine headaches in adults For people living with chronic joint pain, a typical prescription regimen is 500 mg taken twice daily, though your doctor may adjust this based on how you respond and which other medications you take.
In rheumatoid arthritis, naproxen does not slow the underlying autoimmune disease process, but it can meaningfully reduce the day-to-day pain, swelling, and morning stiffness that make the condition so disabling. It is often used alongside disease-modifying drugs that target the immune system directly.
Gout Flares
Acute gout causes sudden, severe joint inflammation, most often in the big toe, and NSAIDs are a first-line treatment for these flares. Early research found that naproxen was effective in alleviating the inflammation of acute gout, with a loading dose of 750 mg followed by 250 mg every eight hours producing rapid improvement in most patients.3PubMed. The treatment of acute gout with naproxen
A more recent head-to-head trial compared naproxen directly to low-dose colchicine, one of the oldest gout treatments available, and found no difference in pain intensity over seven days between the two drugs. Naproxen caused fewer side effects, supporting its use as a first-line treatment for gout flares in primary care when there are no contraindications.4Annals of the Rheumatic Diseases. What Is Naproxen 500 mg Used For? Uses & Side Effects That finding matters because colchicine frequently causes diarrhea and nausea at therapeutic doses, while naproxen tends to be better tolerated during the short course needed for a gout flare.
Menstrual Cramps
Painful periods, or dysmenorrhea, are driven by a surge of prostaglandins released from the uterine lining as it sheds. Those prostaglandins cause the uterus to contract, and the more prostaglandins produced, the worse the cramps. Naproxen sodium sharply reduces prostaglandin levels in menstrual fluid, and research has shown a direct positive correlation between prostaglandin levels and the severity of cramping. The drug was most effective at relieving severe menstrual cramps, though it had less effect on milder pain.5PubMed. Effects of naproxen sodium on menstrual prostaglandins and primary dysmenorrhea
For period pain, many people use the over-the-counter strength (220 mg naproxen sodium) and find it sufficient. When that is not enough, a doctor may prescribe the 500 mg tablet to be taken at the onset of symptoms and then every 12 hours until the cramps pass. Starting naproxen before the cramps peak seems to work better than waiting until pain is already severe, since the drug prevents new prostaglandin formation rather than neutralizing prostaglandins that have already been made.
Migraine
Naproxen 500 mg is a recognized treatment for acute migraine attacks, though it is not the strongest option available. A Cochrane review pooling data from multiple trials found that at two hours, roughly 45% of people taking naproxen had meaningful headache relief compared to 29% on placebo, and about 17% were completely pain-free compared to 8% on placebo.2PubMed Central. Naproxen with or without an antiemetic for acute migraine headaches in adults Naproxen also helped reduce nausea, vomiting, photophobia, and lightheadedness associated with migraine attacks.6PubMed. Treatment of acute migraine attack: naproxen and placebo compared
A separate meta-analysis confirmed that naproxen sodium was more effective than placebo for headache relief at two hours, with a pooled effect showing about 58% better odds of relief and roughly double the chance of being completely pain-free.7PubMed. Meta-analysis of the efficacy and safety of naproxen sodium in the acute treatment of migraine Those numbers are decent but not spectacular. Triptans, the other major class of acute migraine drugs, tend to work faster and for more people. Still, naproxen is useful as a first-line option for mild-to-moderate migraines, or in combination with other medications for more severe attacks. It is also a reasonable choice for people who cannot use triptans due to cardiovascular concerns.
Why Naproxen Lasts Longer Than Other NSAIDs
One of naproxen’s practical advantages is its long duration of action. The average elimination half-life of a 500 mg oral dose is about 25 hours, though the range across individuals can span from roughly 16 to 36 hours.8PubMed. Pharmacokinetics of naproxen, its metabolite O-desmethylnaproxen, and their acyl glucuronides in humans9PubMed Central. The pharmacokinetics of naproxen, its metabolite O-desmethylnaproxen, and their acyl glucuronides in humans. Effect of cimetidine Compare that to ibuprofen, which is typically cleared in four to six hours and needs to be taken three or four times a day to maintain relief. The long half-life is why naproxen 500 mg can be dosed just twice daily for most conditions, reducing the number of pills you need to remember.
Food slows naproxen’s absorption somewhat but does not change how much of the drug ultimately reaches your bloodstream. Research has also shown that even sucralfate, a drug used to coat stomach ulcers, slowed naproxen’s absorption rate but did not reduce the total amount absorbed.10The American Journal of Medicine. Effects of food and sucralfate on the pharmacokinetics of naproxen and ketoprofen in humans In practice, taking naproxen with food is often recommended not because it changes how well the drug works, but because it may reduce stomach upset.
Prescription Versus Over-the-Counter Doses
Naproxen is available in two main forms: naproxen (the free acid) and naproxen sodium (the sodium salt, which absorbs slightly faster). Over-the-counter naproxen sodium comes in 220 mg tablets, typically taken every 8 to 12 hours for general pain relief. Prescription naproxen comes in 250 mg, 375 mg, and 500 mg tablets of the free acid, or 275 mg and 550 mg naproxen sodium tablets. The 500 mg free-acid tablet and the 550 mg naproxen sodium tablet deliver essentially the same amount of active drug.
Interestingly, even over-the-counter doses of naproxen sodium have a noticeable effect on blood platelets. Research found that OTC doses (220 mg taken two or three times daily) produced an antiplatelet effect similar to low-dose aspirin (81 mg) and to prescription-strength naproxen sodium (550 mg twice daily).11PubMed. Platelet inhibitory effects of OTC doses of naproxen sodium compared with prescription dose naproxen sodium and low-dose aspirin This is worth knowing if you take aspirin for heart protection, since the interaction between naproxen and aspirin at the platelet level can be clinically relevant.
Stomach and Digestive Side Effects
The most common side effects of naproxen are gastrointestinal. Because COX-1 helps maintain the protective mucus lining of the stomach, blocking it leaves the stomach more vulnerable to acid damage. This can range from mild indigestion, nausea, or heartburn up through more serious problems like stomach ulcers. NSAID inhibition of COX enzymes, together with acid and digestive juices acting on a weakened lining, can lead to erosions and ulcers, with potential complications including bleeding, protein loss, stricture formation, and perforation.12Gastroenterology. The mechanisms of gastrointestinal damage induced by nonsteroidal anti-inflammatory drugs
The risk of serious stomach problems rises with higher doses, longer use, older age, a history of ulcers, and concurrent use of alcohol or blood thinners. If you need naproxen long-term, your doctor may prescribe a proton pump inhibitor (PPI) to take alongside it.13PubMed Central. Coprescribing proton-pump inhibitors with nonsteroidal anti-inflammatory drugs: risks versus benefits A Cochrane review found that PPIs cut the risk of both stomach and duodenal ulcers by roughly 50 to 60% in people taking NSAIDs regularly.14PubMed Central. Prevention of NSAID-induced gastroduodenal ulcers Taking naproxen with food, using the lowest effective dose, and avoiding alcohol are the simplest ways to reduce everyday stomach discomfort.
Cardiovascular Risk
All NSAIDs carry warnings about increased cardiovascular risk, but naproxen consistently looks like the safest of the group in this regard. A large network meta-analysis of multiple NSAIDs found that while none could be considered completely safe for the cardiovascular system, naproxen seemed least harmful.15PubMed. Cardiovascular safety of non-steroidal anti-inflammatory drugs: network meta-analysis
The PRECISION trial, one of the largest cardiovascular safety trials ever conducted for pain medications, compared naproxen head-to-head against ibuprofen and celecoxib in over 24,000 arthritis patients with cardiovascular risk factors. Major cardiovascular events occurred at similar rates across all three drugs: roughly 2.5% for naproxen, 2.7% for ibuprofen, and 2.3% for celecoxib over the study period.16PubMed. Cardiovascular Safety of Celecoxib, Naproxen, or Ibuprofen for Arthritis In several head-to-head clinical trials, naproxen has not been associated with increased cardiovascular risk compared to other NSAIDs, leading many guidelines to consider it the preferred NSAID for patients with higher cardiovascular risk.17US Pharmacist. Cardiovascular Risk Associated With NSAIDs and COX-2 Inhibitors
The explanation likely lies in naproxen’s antiplatelet effect. Because naproxen inhibits COX-1 in platelets for an extended period (thanks to that long half-life), it has a mild blood-thinning effect similar to low-dose aspirin. Other NSAIDs like ibuprofen and diclofenac do not sustain this effect as consistently, which may be why they carry slightly higher cardiovascular risk. That said, “least harmful” is not the same as “harmless.” If you have established heart disease or significant risk factors, your doctor should weigh the risks and benefits of any NSAID.
Kidney Concerns
Prostaglandins play a key role in maintaining blood flow to the kidneys, especially when the body is stressed by dehydration, low blood pressure, or existing kidney disease. By blocking prostaglandin production, naproxen can reduce blood flow to the kidneys and cause the body to retain salt and water, leading to swelling and increased blood pressure.18PubMed. Acute kidney injury associated with non-steroidal anti-inflammatory drugs In at-risk patients, this vasoconstriction can lead to acute kidney injury.
The risk is highest in people who are already dehydrated, those with pre-existing kidney problems, older adults, and anyone taking other medications that affect the kidneys such as certain blood pressure drugs or diuretics. Both forms of the COX enzyme contribute to kidney function, and their inhibition appears to have somewhat opposing effects on blood pressure and sodium balance.19PubMed Central. Kidney damage from nonsteroidal anti-inflammatory drugs-Myth or truth? Review of selected literature For most healthy people taking naproxen for short courses, kidney problems are uncommon. But long-term use warrants periodic monitoring, especially if you have any of the risk factors mentioned above. Staying well hydrated while taking naproxen is one of the simplest protective measures.
Interactions With Blood Thinners and Aspirin
Naproxen’s interaction with aspirin is one of the more underappreciated drug interactions. If you take low-dose aspirin to protect your heart, naproxen can physically compete with aspirin for the same binding site on the COX-1 enzyme in platelets. Research has shown that naproxen, when present, reduces aspirin’s ability to permanently shut down the enzyme, allowing platelet function to recover faster than it should.20PubMed. Pharmacodynamic interaction of naproxen with low-dose aspirin in healthy subjects This interaction could undermine the sustained platelet inhibition that gives aspirin its cardioprotective effect. Lab testing confirmed that naproxen is among several NSAIDs that interfere with aspirin’s antiplatelet activity, while certain others like diclofenac and acetaminophen do not.21PubMed. Drug/drug interaction of common NSAIDs with antiplatelet effect of aspirin in human platelets
If you need both drugs, many guidelines suggest taking aspirin at least 30 minutes before naproxen to give aspirin time to bind to platelets first. But this is a conversation worth having with your doctor, since the timing matters and the stakes can be high.
Naproxen also increases bleeding risk when combined with anticoagulants. Among patients taking direct oral anticoagulants, concurrent use of antiplatelet drugs was associated with an increased risk of major bleeding.22PubMed Central. Risk of major bleeding among users of direct oral anticoagulants combined with interacting drugs: A population-based nested case-control study Since naproxen itself has antiplatelet properties, combining it with prescription blood thinners amplifies the chance of a bleeding event, whether from the stomach, the urinary tract, or elsewhere.
Naproxen During Pregnancy
The safety of NSAIDs during pregnancy is a concern that comes up frequently. A large prospective cohort study looked at over 6,500 pregnant women who used one or more of four common NSAIDs (ibuprofen, diclofenac, naproxen, and piroxicam) and found no effect on rates of infant survival, congenital malformation, or structural heart defects. No associations with other neonatal complications were found for naproxen specifically.23Wiley Online Library (BJOG). Effects of ibuprofen, diclofenac, naproxen, and piroxicam on the course of pregnancy and pregnancy outcome: a prospective cohort study
However, that reassuring finding applies mainly to use in the first and second trimesters. All NSAIDs, including naproxen, are generally avoided after about 30 weeks of pregnancy because they can cause premature closure of the ductus arteriosus, a blood vessel in the fetal heart that needs to stay open until birth. NSAIDs in the third trimester can also reduce amniotic fluid levels and potentially affect fetal kidney function. For these reasons, most doctors will switch pregnant patients to acetaminophen or other alternatives well before the third trimester.
Other Side Effects Worth Knowing About
Beyond the stomach, heart, and kidney effects already covered, naproxen can cause a handful of other problems, most of which are uncommon but worth recognizing:
- Fluid retention: Mild ankle swelling or puffiness is relatively common, driven by the same prostaglandin-mediated salt retention that affects the kidneys. It typically resolves when the drug is stopped.
- Headache and dizziness: Some people experience central nervous system symptoms, especially at higher doses. These are usually mild.
- Skin reactions: Rashes and, rarely, photosensitivity (increased susceptibility to sunburn) can occur.
- Elevated blood pressure: Because NSAIDs promote sodium retention, they can raise blood pressure by a few points, enough to matter if yours is already borderline or you are on antihypertensive medication.
- Liver enzyme elevations: Occasional mild increases in liver enzymes appear in blood tests but rarely progress to significant liver damage.
Allergic reactions to naproxen can range from hives to more serious swelling of the face or throat. People who have had an allergic reaction to aspirin or another NSAID are at higher risk and should generally avoid naproxen entirely. A subset of people with asthma find that NSAIDs trigger bronchospasm, a phenomenon sometimes called aspirin-exacerbated respiratory disease. If you have nasal polyps and asthma, this is a risk your doctor should evaluate before prescribing naproxen.
Who Should Avoid Naproxen
Certain groups face enough risk that naproxen is either contraindicated or should be used only with careful medical supervision. People with active stomach or intestinal ulcers should not take it. Those with severe kidney disease or severely impaired liver function need to avoid it or use much lower doses under close monitoring. Anyone about to undergo coronary artery bypass surgery should not use any NSAID, including naproxen, in the perioperative period because of increased cardiovascular risk.
Older adults deserve particular caution. Kidney function declines naturally with age, the stomach lining becomes more vulnerable, and the chance of being on interacting medications goes up. Many guidelines recommend that adults over 65 use the lowest effective dose for the shortest possible time, with a PPI co-prescribed if treatment extends beyond a few days. For chronic conditions in this age group, your doctor may prefer topical NSAIDs or other drug classes that avoid the systemic side effects entirely.