Omeprazole is generally well-tolerated and most adverse reactions have been mild and transient.
Nervous System Effects:
Headache, vertigo, dizziness, weakness (asthenia), pain, fatigue, malaise, paresthesia, hemifacial dysesthesia, and psychic disturbances (e.g., depression, aggression, confusion, anxiety, agitation, insomnia, nervousness, tremors, apathy, dream abnormalities, somnolence, and hallucinations) have been reported but not directly attributable to the drug in many cases.
Constipation and diarrhea, nausea, vomiting, abdominal pain, flatulence, and acid regurgitation. Occasionally, dysphagia, abdominal swelling, irritable colon, fecal discoloration, pancreatitis (sometimes fatal), esophageal candidiasis, gastric hypermotility, mucosal atrophy of the tongue, taste disturbances, anorexia, stomatitis, dry mouth, dysgeusia, and tongue discoloration have been reported. Benign gastric fundic polyps have been rarely reported but resolve upon discontinuation of omeprazole therapy.
Back pain, muscle cramps, myalgia, muscle weakness, arthralgia, joint pain, and leg pain have been occasionally reported with the use of omeprazole.
Observational studies have shown that long term use and high dose proton pump inhibitor therapy may increase the risk of hip fracture in patients 50 years and older.
Dermatologic and Sensitivity Reactions:
Rash, severe generalized reactions (e.g., toxic epidermal necrolysis), Stevens-Johnson Syndrome, erythema multiforme, exfoliative dermatitis, and lichenoid eruptions. Other effects include skin inflammation, photosensitivity, urticaria, purpura and/or petechiae, bullous eruption, angioedema, pruritus, alopecia, dry skin, and hyperhydrosis. Allergic reactions, including rare cases of anaphylaxis have also been reported.
Acute interstitial nephritis and sexual disturbances such as priaprism have been occasionally reported with the use of omeprazole. Urinary tract infection, microscopic pyuria, urinary frequency, elevated serum creatinine concentration, proteinuria, hematuria, glycosuria, and testicular pain have also been reported but in many cases not attributed to omeprazole.
There have been rare reports of increases in serum aspartate aminotransferase (AST), alanine aminotransferase (ALT), γ-glutamyltransferase (GGT), γ-glutamyltranspeptidase (GGTP), alkaline phosphatase and bilirubin concentrations. Symptomatic liver disease including hepatocellular, cholestatic, or mixed hepatitis, jaundice, liver necrosis, hepatic failure, and hepatic encephalopathy have occurred rarely.
Upper respiratory tract infections and cough. Epistaxis and pharyngeal pain have been reported occasionally. Acute respiratory distress syndrome, respiratory failure, and pneumothorax have occurred in some patients. Other effects that were reported with combined omeprazole and clarithromycin therapy were rhinitis, pharyngitis and flu syndrome.
The use of proton pump inhibitors has been associated with an increased risk of developing community-acquired pneumonia. These drugs should only be used when clearly needed using the lowest effective dose in patients with severe community-acquired pneumonia.
Chest pain, angina pectoris, tachycardia, bradycardia, palpitation, hypotension, hypertension, and peripheral edema have been reported occasionally. Atrial fibrillation, ventricular tachycardia, bradycardia, palpitation, and peripheral edema have also been reported.
Leukocytosis, neutropenia, pancytopenia, agranulocytosis, leukopenia, anemia, hemolytic anemia, and thrombocytopenia have been reported rarely.
Blurred vision, ocular irritation, dry eye syndrome, optic atrophy, anterior ischemic optic neuropathy, optic neuritis, and double vision have been reported.
Other Adverse Effects:
Fever, tinnitus, weight gain, acute gout, hypophosphatemia, hypocalcemia, fluid overload, hyperglycemia, hypomagnesemia, hypokalemia, sweating, hyponatremia, and otitis media. Edema, gynecomastia, oral candidiasis, and candidal infection have also occurred.