Indomethacin is a powerful anti-inflammatory medication used to treat several painful conditions, including rheumatoid arthritis, osteoarthritis, gout flares, ankylosing spondylitis, and certain rare headache disorders. It belongs to the class of nonsteroidal anti-inflammatory drugs (NSAIDs) but is considered stronger than common over-the-counter options like ibuprofen or naproxen, which is why it requires a prescription.
How Indomethacin Works
Like other NSAIDs, indomethacin reduces pain and inflammation by blocking enzymes called COX-1 and COX-2. These enzymes produce prostaglandins, chemicals your body releases in response to injury or disease that trigger swelling, pain, and fever. What makes indomethacin unusual is how tightly it binds to these enzymes. Most NSAIDs latch on temporarily, but indomethacin locks into the enzyme’s active site in a way that is functionally irreversible. A small structural feature on the molecule, a methyl group on its indole ring, inserts into a pocket within the enzyme and anchors it there. This tight binding is one reason indomethacin is more potent than many other NSAIDs, and also why it tends to cause more side effects.
Arthritis and Joint Inflammation
Indomethacin is FDA-approved for moderate to severe rheumatoid arthritis (including acute flares), moderate to severe osteoarthritis, and ankylosing spondylitis, a type of inflammatory arthritis that primarily affects the spine. For these chronic conditions, treatment typically starts at a low dose taken two or three times daily, then gradually increases over several weeks until symptoms improve or the maximum daily limit is reached.
It’s not a first-line choice for most people with arthritis. Doctors generally try milder NSAIDs first and turn to indomethacin when those aren’t enough, particularly for ankylosing spondylitis, where it has a long track record of effectiveness.
Acute Gout Flares
Gout attacks are one of the most common reasons indomethacin gets prescribed. When uric acid crystals build up in a joint and trigger sudden, severe inflammation, indomethacin can provide noticeable pain relief within 2 to 4 hours. Tenderness and heat in the joint typically subside within 24 to 36 hours, and swelling gradually disappears over 3 to 5 days.
For gout, the dosing strategy is different from chronic arthritis. You take a higher dose three times daily until the pain becomes tolerable, then taper off quickly and stop. It’s meant as a short burst of treatment, not something you stay on.
Headache Disorders That Respond Only to Indomethacin
One of indomethacin’s most distinctive roles is in diagnosing and treating a small group of rare headache syndromes. Two conditions, hemicrania continua and paroxysmal hemicrania, respond “absolutely” to indomethacin according to the International Headache Society. In fact, a complete response to indomethacin is part of the official diagnostic criteria for these disorders. If the headache goes away with indomethacin and nothing else works, that itself helps confirm the diagnosis.
Hemicrania continua causes a continuous, one-sided headache that varies in intensity, sometimes accompanied by tearing, nasal congestion, or eyelid drooping on the affected side. Paroxysmal hemicrania produces shorter but severe attacks on one side of the head, occurring multiple times per day. For people with these conditions, indomethacin can be life-changing, often eliminating pain entirely. Maintenance doses are typically lower than the initial therapeutic dose.
Use in Premature Infants
In a completely different setting, indomethacin has been used in neonatal intensive care to close a heart defect called patent ductus arteriosus (PDA). Before birth, a small blood vessel called the ductus arteriosus connects two major arteries and normally closes on its own shortly after delivery. In premature infants, it sometimes stays open, forcing the heart to work harder. Because prostaglandins help keep this vessel open, blocking their production with indomethacin can encourage it to close.
A large body of research, including 19 randomized trials involving nearly 2,900 infants, found that preventive use of indomethacin in extremely low birth weight babies significantly reduced rates of symptomatic PDA and severe bleeding in the brain. More recently, ibuprofen has become the more common choice for treating PDA because it has a similar closure rate with a better safety profile, but indomethacin remains an option.
Available Forms
Indomethacin comes in oral capsules (both immediate-release and extended-release), a rectal suppository, and an injectable form. Oral capsules are by far the most common for adults with arthritis, gout, or headache disorders. Suppositories may be used when someone can’t take medication by mouth, such as during severe nausea. The injectable form is primarily used in hospital settings, including for neonatal PDA closure.
How Quickly It Works
For acute conditions like gout, you can expect meaningful pain relief within a few hours. For chronic inflammatory conditions like rheumatoid arthritis or ankylosing spondylitis, it may take days to weeks of consistent use to reach full benefit. The medication has a half-life of about 4.5 hours, which is why it’s typically taken multiple times per day unless you’re using an extended-release capsule.
Risks and Side Effects
Indomethacin carries the same FDA boxed warnings as all prescription NSAIDs. The first warning concerns cardiovascular risk: NSAIDs increase the chance of serious blood clots, heart attack, and stroke. This risk can appear early in treatment and may grow with longer use. Indomethacin is specifically contraindicated after coronary artery bypass graft surgery.
The second boxed warning addresses the gastrointestinal tract. Indomethacin can cause bleeding, ulceration, or perforation of the stomach or intestines. These events can happen at any point during treatment, sometimes without any warning symptoms beforehand. Older adults face a higher risk of these serious GI complications.
Common, less serious side effects include headache, dizziness, nausea, and stomach upset. Because indomethacin is one of the more potent NSAIDs, these side effects tend to be more frequent than with milder alternatives. Taking it with food or milk can help reduce stomach irritation. Kidney function can also be affected, particularly in people who already have impaired kidneys or who are dehydrated, so doctors often monitor bloodwork during longer courses of treatment.
Who Should Avoid It
People with a history of allergic reactions to aspirin or other NSAIDs should not take indomethacin. It’s also avoided in late pregnancy because prostaglandin inhibition can cause premature closure of the ductus arteriosus in the fetus, the same mechanism that makes it useful for treating PDA in premature newborns after birth. Anyone with active GI bleeding or a recent history of stomach ulcers is generally not a candidate. Because of its cardiovascular risks, people with established heart disease or significant risk factors need careful evaluation before starting treatment.