Nearly all patients benefit from an ulcer protective drug (e.g. highly dosed antacids, ranitidine 150 mg at bedtime, or omeprazole 20 mg at bedtime). Other common gastrointestinal complaints, including dyspepsia, heartburn and mild diarrhea are less serious and rarely require discontinuation of indometacin. Many NSAIDs, but particularly indometacin, cause lithium retention by reducing its excretion by the kidneys. Thus indometacin users have an elevated risk of lithium toxicity. For patients taking lithium (e.g. for treatment of depression or bipolar disorder), less toxic NSAIDs such as sulindac or aspirin are preferred. All NSAIDs, including indometacin, also increase plasma renin activity and aldosterone levels, and increase sodium and potassium retention. Vasopressin activity is also enhanced. Together these may lead to:

Edema (swelling due to fluid retention)
Hyperkalemia (high potassium levels)
Hypernatremia (high sodium levels)
HypertensionElevations of serum creatinine and more serious renal damage such as acute kidney failure, chronic nephritis and nephrotic syndrome, are also possible. These conditions also often begin with edema and high potassium levels in the blood. Paradoxically yet uncommonly, indometacin can cause headache (10 to 20%), sometimes with vertigo and dizziness, hearing loss, tinnitus, blurred vision (with or without retinal damage). There are unsubstantiated reports of worsening Parkinsons disease, epilepsy, and psychiatric disorders. Cases of life-threatening shock (including angioedema, sweating, severe hypotension and tachycardia as well as acute bronchospasm), severe or lethal hepatitis and severe bone marrow damage have all been reported. Skin reactions and photosensitivity are also possible side effects.
Clinical indications for indometacin include:Joint diseases

rheumatoid arthritis
ankylosing spondylitis
osteoarthritis
gouty arthritis
acute painful shoulder bursitis or tendinitisHeadaches

Trigeminal autonomic cephalgias
Paroxysmal hemicranias
Chronic paroxysmal hemicrania
Episodic paroxysmal hemicrania
Hemicrania continua
Valsalva-induced headaches
Primary cough headache
Primary exertional headache
Primary headache associated with sexual activity (preorgasmic and orgasmic)
Primary stabbing headache (jabs and jolts syndrome)
Hypnic headacheOthers

Patent ductus arteriosus

Contraindications
Concurrent peptic ulcer, or history of ulcer disease
Allergy to indometacin, aspirin, or other NSAIDs
Roux-en-Y gastric bypass and gastric sleeve patients
Patients with nasal polyps reacting with an angioedema to other NSAIDs
Children under 2 years of age (with the exception of neonates with patent ductus arteriosus)
Severe pre-existing renal and liver damage
Caution: pre-existing bone marrow damage (frequent blood cell counts are indicated)
Caution: bleeding tendencies of unknown origin (indometacin inhibits platelet aggregation)
Caution: Parkinsons disease, epilepsy, psychotic disorders (indometacin may worsen these conditions)
Concurrent with potassium sparing diuretics
Patients who have a patent ductus arteriosus dependent heart defect (such as transposition of the great vessels)
Significant hypertension (high blood pressure)
Concomitant administration of lithium salts (such as lithium carbonate)

Adverse effects
In general, adverse effects seen with indometacin are similar to all other NSAIDs. For instance,  indometacin inhibits both cyclooxygenase-1 and cyclooxygenase-2, which then inhibits the production of prostaglandins in the stomach and intestines responsible for maintaining the mucous lining of the gastrointestinal tract. Indometacin, therefore, like other non-selective COX inhibitors, can cause peptic ulcers. These ulcers can result in serious bleeding or perforation, requiring hospitalization of the patient. To reduce the possibility of peptic ulcers, indometacin should be prescribed at the lowest dosage needed to achieve a therapeutic effect, usually between 50 and 200 mg/day. It should always be taken with food.