Pharmacology · Nonsteroidal anti-inflammatory drugs (NSAIDs)

Naproxen !

A long-acting non-selective NSAID used in arthritis, acute gout and dysmenorrhoea. It can interfere with the antiplatelet effect of acetylsalicylic acid.

Updated 2026-11-01

Class: Nonsteroidal anti-inflammatory drugs (NSAIDs)
Enzyme: Cyclooxygenase 1 and 2 (COX-1/COX-2)
ATC code: M01AE02

Cyclooxygenase 1 and 2 (COX-1/COX-2)Naproxen

The figure shows naproxen in the channel of mouse COX-2, which keeps the same site as the human enzyme.

Target in 3D: Cyclooxygenase 1 and 2 (COX-1/COX-2). PDB structure 3NT1 (RCSB PDB, public domain). View the structure at RCSB PDB

Mechanism of action

Naproxen, a propionic acid derivative like ibuprofen, reversibly inhibits COX-1 and COX-2 and lowers the prostaglandins of inflammation, pain and fever. Its long half-life means that in some people platelet inhibition lasts through the whole dosing interval.

Reversibly occupies the channel of COX-1 and COX-2
Prostaglandin synthesis falls
Less inflammation, pain and fever
Its long half-life sustains the effect between doses

Pharmacokinetics

Absorption: Rapid and nearly complete oral absorption.
Distribution: Highly protein bound, saturating at high doses; the free fraction rises in older adults.
Metabolism: Liver to 6-O-desmethylnaproxen; both are conjugated as acyl glucuronides.
Elimination: Almost all in the urine, as conjugates.
Half-life: Long: about 12 to 17 hours.

Indications

Rheumatoid arthritis Rheumatoid arthritis →
Osteoarthritis Knee Osteoarthritis →
Ankylosing spondylitis Ankylosing spondylitis →
Acute gout Gout →
Primary dysmenorrhoea Dysmenorrhoea →
Tendinitis, bursitis and pain in general

Adverse effects

Common

Constipation and gas
Headache, dizziness and drowsiness
Trouble sleeping
Ringing in the ears

Contraindications

Hypersensitivity to the drug
Asthma, urticaria or another allergic reaction after acetylsalicylic acid or another NSAID
The setting of coronary artery bypass graft (CABG) surgery

Key interactions

Low-dose acetylsalicylic acid: Naproxen can interfere with its antiplatelet effect, above all when taken before the acetylsalicylic acid.
Anticoagulants (warfarin), antiplatelet agents, SSRIs and SNRIs: Add to the risk of bleeding.
ACE inhibitors, ARBs and diuretics: Blunt their antihypertensive and diuretic effect; in older or volume-depleted patients they can precipitate acute kidney injury.
Lithium: Raise its blood levels by lowering renal clearance.
Methotrexate: Raise the risk of methotrexate toxicity (neutropenia, thrombocytopenia, kidney damage).

What is monitored

Signs of gastrointestinal bleeding
Kidney function and potassium
Blood pressure and oedema

Administration and safety

There are naproxen and naproxen sodium; the two are not added together, nor with other over-the-counter NSAIDs.
Over-the-counter naproxen may be taken with food or milk to prevent nausea.

Nursing care

Before starting: history of ulcer, bleeding, kidney or cardiovascular disease, or asthma with NSAIDs.
Watch for black stools, vomiting blood, abdominal pain and signs of anaemia.
Watch blood pressure, oedema, urine output and creatinine, above all in older patients or those on diuretics.
In patients on acetylsalicylic acid for cardiovascular protection, report the possible effect of naproxen on its antiplatelet action.

Pregnancy and breastfeeding

From about week 20 it can cause fetal kidney dysfunction with oligohydramnios, and from about week 30 premature closure of the ductus arteriosus; so use is limited between those weeks and avoided late in pregnancy.

Test yourself

Think of the answer, then tap the question to see it.

What practical advantage does naproxen's long half-life give?

It keeps working with fewer daily doses than ibuprofen and, in some people, sustains platelet inhibition through the whole interval.

How does naproxen interact with low-dose acetylsalicylic acid?

It can occupy platelet COX-1 and get in the way of acetylation by acetylsalicylic acid, reducing its antiplatelet effect, above all when taken first.

Why can naproxen be more toxic in older adults?

Because its free fraction in plasma rises, which contributes to more gastrointestinal adverse effects.

Add to my cards (3)

← Back to the class: Nonsteroidal anti-inflammatory drugs (NSAIDs)

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: Naproxen: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); NAPROXEN tablet (DailyMed (U.S. National Library of Medicine), 2026); Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed., ch. 42 (McGraw Hill, 2023); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake

Representative model, for educational purposes only.