| The most common side effects (1-10% of patients) are headache, abdominal pain, constipation, diarrhoea, flatulence and nausea/vomiting.The following adverse drug reactions have been identified or suspected in the clinical trials programme for omeprazole and post-marketing. None was found to be dose-related. Adverse reactions listed below are classified according to frequency and System Organ Class (SOC). Frequency categories are defined according to the following convention: Very common ( 1/10), Common ( 1/100 to < 1/10), Uncommon ( 1/1,000 to < 1/100), Rare ( 1/10,000 to < 1/1,000), Very rare (< 1/10,000), Not known (cannot be estimated from the available data).SOC/frequency | Adverse reaction | Blood and lymphatic system disorders | Rare: | Leukopenia, thrombocytopenia | Very rare: | Agranulocytosis, pancytopenia | Immune system disorders | Rare: | Hypersensitivity reactions e.g. fever, angioedema and anaphylactic reaction/shock | Metabolism and nutrition disorders | Rare: | Hyponatraemia | Very rare: | Hypomagnesaemia | Psychiatric disorders | Uncommon: | Insomnia | Rare: | Agitation, confusion, depression | Very rare: | Aggression, hallucinations | Nervous system disorders | Common: | Headache | Uncommon: | Dizziness, paraesthesia, somnolence | Rare: | Taste disturbance | Eye disorders | Rare: | Blurred vision | Ear and labyrinth disorders | Uncommon: | Vertigo | Respiratory, thoracic and mediastinal disorders | Rare: | Bronchospasm | Gastrointestinal disorders | Common: | Abdominal pain, constipation, diarrhoea, flatulence, nausea/vomiting | Rare: | Dry mouth, stomatitis, gastrointestinal candidiasis | Hepatobiliary disorders | Uncommon: | Increased liver enzymes | Rare: | Hepatitis with or without jaundice | Very rare: | Hepatic failure, encephalopathy in patients with pre-existing liver disease | Skin and subcutaneous tissue disorders | Uncommon: | Dermatitis, pruritus, rash, urticaria | Rare: | Alopecia, photosensitivity | Very rare: | Erythema multiforme, Stevens-Johnson syndrome, toxic epidermal necrolysis (TEN) | Musculoskeletal and connective tissue disorders | Rare: | Arthralgia, myalgia | Very rare: | Muscular weakness | Renal and urinary disorders | Rare: | Interstitial nephritis | Reproductive system and breast disorders | Very rare: | Gynaecomastia | General disorders and administration site conditions | Uncommon: | Malaise, peripheral oedema | Rare: | Increased sweating | Irreversible visual impairment has been reported in isolated cases of critically ill patients who have received omeprazole intravenous injection, especially at high doses, but no causal relationship has been established. | |