Naproxen Side Effects: What You Need to Know

Naproxen is a non-steroidal anti-inflammatory drug (NSAID) widely prescribed for pain relief, inflammation and fever.

Like all NSAIDs, it carries a well-documented side-effect profile that patients should understand before starting treatment.

The most frequently reported side effects involve the gastrointestinal tract.

Up to 15% of patients taking naproxen 500 mg twice daily experience some degree of stomach discomfort during the first week of treatment.

• Heartburn and indigestion: reported by roughly 10% of users in clinical trials
• Nausea: affects approximately 7% of patients, often improving after eating
• Abdominal pain: a dull, central discomfort that tends to settle within 3 to 5 days
• Constipation or diarrhoea: occurs in around 3 to 5% of patients
• Bloating and flatulence: usually mild and self-limiting

Other common side effects outside the gut include headache (reported in about 9% of users), dizziness (3 to 4%) and mild fluid retention.

Some patients notice slight drowsiness, particularly at higher doses. These effects are generally dose-dependent, meaning they are more likely at 1,000 mg per day than at lower doses.

Taking naproxen with or immediately after food significantly reduces the risk of gastric irritation.

Your pharmacist may also recommend a proton pump inhibitor such as omeprazole if you need naproxen for longer than a few weeks.

Although serious side effects of naproxen are uncommon, they can be significant and require prompt medical attention. Being aware of the warning signs allows you to act quickly if they occur.

Gastrointestinal bleeding and ulceration

All NSAIDs increase the risk of upper GI bleeding. The absolute risk with naproxen is estimated at 1 to 2 per 100 patient-years of use.

Symptoms to watch for include black or tarry stools, vomiting blood or material that looks like coffee grounds, and unexplained severe stomach pain.

The risk rises substantially in patients over 65, those with a previous ulcer history, and anyone taking concurrent corticosteroids or anticoagulants.

Cardiovascular events

NSAIDs as a class carry a small increase in cardiovascular risk. Among the traditional NSAIDs, naproxen appears to have the most favourable cardiovascular profile, with a relative risk close to 1.

0 for major vascular events in the PRECISION trial. Nevertheless, the MHRA advises caution in patients with established heart disease.

Kidney effects

Naproxen inhibits prostaglandin synthesis in the kidneys, which can reduce renal blood flow.

This is particularly relevant for patients who are dehydrated, elderly or already have impaired kidney function.

Signs of kidney problems include reduced urine output, swollen ankles and unexplained weight gain.

Allergic reactions

Rarely, naproxen can trigger bronchospasm, urticaria or anaphylaxis. Patients with aspirin-sensitive asthma are at greatest risk.

Seek emergency care for facial swelling, wheezing or difficulty breathing.

Certain patient groups face a higher likelihood of experiencing side effects from naproxen.

Understanding your individual risk helps you and your prescriber make an informed decision about whether naproxen is the right choice.

Older adults (over 65)

Age is one of the strongest risk factors for NSAID-related complications. The BNF recommends that elderly patients use the lowest effective dose for the shortest possible duration.

A gastroprotective agent such as omeprazole 20 mg daily is recommended when naproxen treatment exceeds one week in this age group.

Patients with a history of peptic ulcer disease

A previous upper GI bleed or ulcer increases the risk of recurrence by two to four times when an NSAID is introduced.

In many cases, an alternative analgesic such as paracetamol is preferred.

People with kidney or liver impairment

Reduced organ function slows the clearance of naproxen, raising plasma levels and the chance of toxicity.

The BNF advises dose reduction or avoidance in moderate to severe hepatic impairment and in patients with an eGFR below 30 mL/min.

Those on multiple medicines

Concurrent use of anticoagulants (warfarin, DOACs), SSRIs, corticosteroids or other NSAIDs significantly amplifies the bleeding risk.

Always tell your prescriber about every medicine you take, including over-the-counter products like ibuprofen.

Pregnant or breastfeeding women

Naproxen is contraindicated from 30 weeks of pregnancy and should be used with caution earlier in pregnancy. Small amounts pass into breast milk, so medical advice is essential before use.

There are several practical strategies that can help minimise side effects while you are taking naproxen.

Many of these are simple lifestyle adjustments that make a measurable difference to tolerability.

Take it with food

Swallowing naproxen tablets with or just after a meal creates a food buffer in the stomach, reducing direct contact between the drug and the gastric lining.

This single step can cut the incidence of dyspepsia by roughly half.

Use the lowest effective dose

Naproxen is available in 250 mg and 500 mg tablets. Starting at the lower dose and increasing only if needed keeps side-effect exposure to a minimum.

For acute musculoskeletal pain, short courses of 5 to 7 days are often sufficient.

Stay well hydrated

Drinking at least 1.5 to 2 litres of water daily supports kidney perfusion and helps offset the fluid-retaining tendency of NSAIDs.

Avoid excessive caffeine and alcohol, which can worsen gastric irritation.

Consider gastroprotection

If you need naproxen for more than two weeks, or if you have risk factors for GI bleeding, a proton pump inhibitor (PPI) such as omeprazole or lansoprazole provides effective protection.

NICE Clinical Knowledge Summaries recommend co-prescribing a PPI for all high-risk patients.

Monitor your symptoms

Keep a brief daily note of any new symptoms during the first week of treatment.

This helps your doctor distinguish drug-related effects from other causes and decide whether to continue, adjust or switch your medication.

Patients often ask how naproxen compares to other painkillers in terms of safety. While every NSAID shares a core set of risks, there are meaningful differences between individual drugs.

Naproxen vs ibuprofen

Both belong to the same drug class, but naproxen has a longer half-life (12 to 17 hours versus 2 to 4 hours for ibuprofen), so it is taken less frequently.

The GI side-effect rates are broadly similar at equivalent anti-inflammatory doses. However, naproxen consistently shows a lower cardiovascular risk than ibuprofen in large meta-analyses.

For more detail, see our dedicated comparison at naproxen and ibuprofen.

Naproxen vs diclofenac

Diclofenac carries a higher cardiovascular risk than naproxen.

The Coxib and Traditional NSAID Trialists' Collaboration found that diclofenac 150 mg daily increased the rate of major vascular events by about a third, whereas naproxen 1,000 mg daily did not.

For this reason, NICE guidance favours naproxen over diclofenac when an oral NSAID is needed in patients with cardiovascular risk factors.

Naproxen vs paracetamol

Paracetamol is not an NSAID and works differently. It has a much lower risk of GI and cardiovascular side effects but provides less anti-inflammatory benefit.

For conditions driven primarily by inflammation, such as rheumatoid arthritis or acute gout, naproxen is usually more effective.

See our guide on naproxen and paracetamol for advice on combining the two safely.

Your prescriber will weigh these trade-offs against your medical history to recommend the most appropriate option.

Most naproxen side effects are mild and resolve on their own, but certain symptoms require urgent medical assessment.

Knowing the difference between a minor nuisance and a potentially serious reaction is important for your safety.

Seek same-day medical advice if you experience:

• Persistent stomach pain that does not improve after stopping naproxen
• Unusual bruising or bleeding from the gums
• Swollen ankles or unexplained weight gain of more than 1 kg in a few days
• A skin rash, itching or hives that develop after taking naproxen
• Dark urine or reduced urine output lasting more than 24 hours

Call 999 or go to A&E immediately if you notice:

• Black, tarry or bloody stools
• Vomiting blood or dark, coffee-ground-like material
• Chest pain, sudden breathlessness or weakness on one side of the body
• Severe swelling of the face, lips, tongue or throat
• Difficulty breathing or wheezing that comes on rapidly

If in doubt, contact NHS 111 for advice. It is always better to check than to ignore a warning sign.

When you attend, bring your medication packet so the clinician can see the exact product and dose you have been taking.

For broader NHS guidance on naproxen, see our naproxen NHS information page.