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Omeprazole Side Effects

For the Consumer

Applies to omeprazole: oral capsule delayed release, oral packet, oral powder for suspension, oral tablet delayed release

As well as its needed effects, omeprazole may cause unwanted side effects that require medical attention.

Severity: Major

If any of the following side effects occur while taking omeprazole, check with your doctor immediately:

  • Back, leg, or stomach pain
  • bleeding or crusting sores on the lips
  • blisters
  • bloody or cloudy urine
  • chills
  • continuing ulcers or sores in the mouth
  • difficult, burning, or painful urination
  • fever
  • frequent urge to urinate
  • general feeling of discomfort or illness
  • joint pain
  • loss of appetite
  • muscle aches or cramps
  • pain
  • red or irritated eyes
  • redness, tenderness, itching, burning, or peeling of the skin
  • skin rash or itching
  • sore throat
  • sores, ulcers, or white spots on the lips, in the mouth, or on the genitals
  • unusual bleeding or bruising
  • unusual tiredness or weakness
Incidence not known:
  • Drowsiness
  • fast, racing, or uneven heartbeat
  • mood or mental changes
  • muscle spasms (tetany) or twitching seizures
  • nausea or vomiting
  • trembling

If any of the following symptoms of overdose occur while taking omeprazole, get emergency help immediately:

Symptoms of overdose:
  • Blurred vision
  • confusion
  • dryness of the mouth
  • flushing
  • headache
  • increased sweating

Severity: Minor

Some omeprazole side effects may not need any medical attention. As your body gets used to the medicine these side effects may disappear. Your health care professional may be able to help you prevent or reduce these side effects, but do check with them if any of the following side effects continue, or if you are concerned about them:

Less common:
  • Body aches or pain
  • chest pain
  • constipation
  • cough
  • diarrhea or loose stools
  • difficulty with breathing
  • dizziness
  • ear congestion
  • gas
  • heartburn
  • loss of voice
  • muscle pain
  • nasal congestion
  • runny nose
  • sneezing
  • unusual drowsiness

For Healthcare Professionals

Applies to omeprazole: compounding powder, oral delayed release capsule, oral delayed release tablet, oral powder for reconstitution, oral powder for reconstitution delayed release, oral suspension


Omeprazole is generally well tolerated. Any drug which increases gastric pH would be anticipated to stimulate release of gastrin. Animal studies have demonstrated an increase in plasma gastrin concentrations following the administration of omeprazole. In addition, long term animal studies have revealed a dose-related increase in the incidence of gastric enterochromaffin-like (ECL) cell carcinoids. This has given rise to concern regarding the safety of long-term administration of omeprazole in humans. However, to date, long-term human studies of up to six years duration have not found any suggestion of gastric carcinoid formation due to omeprazole use.

In humans, plasma gastrin levels rise within days of initial treatment, generally peaking by 2 to 4 months. The usual increase is 2 to 4 fold over baseline, although some patients experience gastrin levels greater than 10 times normal. Hyperplasia of gastric enterochromaffin-like cells has been observed with long-term use, but no evidence of dysplasia, carcinoid tumors, or other neoplastic changes have been noted in humans.[Ref]


Gastric polyposis have been reported in three of eleven patients treated with long-term omeprazole therapy (20 to 40 mg daily). Hyperplastic and fundic gland polyps developed in the stomach of these patients. Neither dysplasia nor malignancy was present. The significance of these findings from a small case series is unknown. Controlled studies are needed to fully evaluate this effect.

Ninety-one patients receiving long-term maintenance therapy for gastroesophageal reflux disease were followed for 5 years. Hyperplasia of gastric enterochromaffin-like cells was noted in 20% of patients and atrophic gastritis in 25%. Effects were more pronounced in patients with very high serum gastrin levels. The significance of these observed changes is unknown. No evidence of dysplasia, carcinoid, or other forms of neoplasia were noted.[Ref]

Gastrointestinal side effects have included diarrhea (3.0% to 3.7%), abdominal pain (2.4%), nausea (2.2% to 4%), vomiting (1.5% to 3.2%), constipation (1.1%), anorexia, irritable colon, flatulence, dry mouth, esophageal candidiasis, and persistent achlorhydria in a Zollinger-Ellison patient. Gastric polyps, hyperplasia of gastric enterochromaffin-like cells, and atrophic gastritis have been reported after long-term therapy. Campylobacter gastroenteritis has been identified in one case-control study.

Rare cases of pancreatitis, some fatal, have been reported during the post marketing period.[Ref]


Endocrine side effects have included gynecomastia, breast enlargement in females, and breast tenderness.[Ref]


Hepatic side effects have included elevations in serum transaminases, alkaline phosphatase, bilirubin, and rare cases of hepatitis and hepatic encephalopathy. Fatal fulminant hepatic failure attributed to omeprazole has also been reported.[Ref]

A 62-year-old man with erosive esophagitis developed signs and symptoms of hepatic disease 17 days after the start of therapy with omeprazole 20 mg per day. Five days after presentation, the patient died from complications associated with fulminant hepatic failure. Autopsy findings included massive central zone necrosis and hemorrhage with proliferation of bile ducts.[Ref]


Renal side effects have included elevations in serum creatinine, rare reports of interstitial nephritis, and renal failure.[Ref]


The absorption of cyanocobalamin (vitamin B12) has been studied before and after administration of omeprazole 20 mg or 40 mg per day for 14 days in ten healthy subjects. Omeprazole produced a dose-dependent reduction in protein-bound cyanocobalamin absorption. Because the effects of long-term omeprazole therapy on cyanocobalamin disposition are unknown, it may be prudent to monitor cyanocobalamin levels in patients receiving long-term omeprazole therapy.[Ref]

Hematologic side effects have included rare reports of hemolytic anemia, pancytopenia, thrombocytopenia, neutropenia, anemia, agranulocytosis and leukocytosis.[Ref]


Respiratory side effects have included cough, and rare reports of epistaxis and pharyngeal pain.[Ref]

A 42-year-old female with postoperative heartburn experienced chronic, persistent cough coincident with omeprazole therapy. The cough was permanent, dry, exhausting, and worsened at night. Omeprazole treatment was continued for 4 months because the persistent cough was thought to be related to gastroesophageal reflux disease. However, no cause of the chronic cough was identified. After omeprazole was discontinued, the cough resolved.[Ref]

Nervous system

Nervous system side effects have included headache, dizziness, somnolence, vertigo, hemifacial dysesthesia and numbness, paresthesias of the extremities, seizures, and a report of reversible gait ataxia.[Ref]


Cardiovascular side effects have been reported rarely. These have included angina, tachycardia, bradycardia, palpitations, hypertension, and peripheral edema.[Ref]


Cutaneous leukocytoclastic vasculitis has been reported to occur in a 71-year-old woman. Three weeks after the start of omeprazole 20 mg daily for epigastric pain, patient presented with palpable skin rash on both hands and legs and the abdomen, accompanied with pruritus. Histopathological studies of affected tissue confirmed small vessel vasculitis. Skin lesions completely resolved within a few days after discontinuation of omeprazole treatment.

An 81-year-old female with severe reflux esophagitis experienced dermatomyositis coincident with omeprazole therapy. She presented with a progressive pruritic erythematous eruption which began as a vesicular rash on her dorsal hands and then spread to her face and most of her lower limbs. Three days prior to the onset of skin eruption, she had started omeprazole 40 mg daily. She was diagnosed with dermatomyositis. Omeprazole was replaced with ranitidine and mometasone furoate ointment twice daily was administered for the rash. After 1 week, her rash had also settled significantly with less erythema and edema, particularly over her dorsal hands.[Ref]

Dermatologic side effects have included rash and rare reports of pruritus, alopecia, dry skin, hyperhidrosis, and cases of disseminated epidermal necrosis, furunculosis, and exfoliative dermatitis. At least one case of vasculitis has been reported, in addition to a case of dermatomyositis.[Ref]


Hypersensitivity side effects have included urticaria and angioedema. One case report of anaphylaxis upon a second use of omeprazole is documented.[Ref]


Metabolic side effects have included hypoglycemia, hyponatremia, weight gain, and increased uric acid levels. It has also been reported that omeprazole may cause hypomagnesemia if taken for prolonged periods of time (in most cases, longer than one year). Patients who develop hypomagnesemia may experience seizures, dizziness, abnormal or fast heart beat, or skipped heartbeat, jitteriness, jerking movements or tremors, muscle weakness, spasms of the hands and feet, cramps or muscle aches, and spasm of the voice box.[Ref]

A case report of omeprazole associated with symptomatic hyponatremia, probably secondary to inappropriate ADH secretion, has been reported.

Two case reports have suggested that omeprazole may rarely cause increased uric acid levels and acute gout attacks.

Two cases of hospitalized patients with refractory chronic hypokalemia and hypocalcemia secondary to hypomagnesemia were resolved after withdrawal of omeprazole.[Ref]


Psychiatric side effects have been reported rarely. These have included depression, nervousness, hallucinations, insomnia, anxiety, dream disturbances, and apathy.[Ref]


Genitourinary side effects have included impotence and rare reports of urinary tract infection, pyuria, urinary frequency, proteinuria, hematuria, glycosuria, and testicular pain.[Ref]


The risk of hip fracture was significantly increased among patients prescribed long-term high dose PPIs.

A 71-year-old male was admitted to the emergency department complaining of severe epigastric pain. He was administered a single dose of omeprazole 40 mg. After 12 hours, the epigastric pain continued and the patient was hospitalized. Blood analysis at this time showed an increase in creatinine kinase, creatinine kinase isoenzymes, and myoglobin levels, without concomitant symptoms of muscle injury. Omeprazole-induced myopathy was suspected, the drug discontinued, and no other gastrointestinal drugs were given. After one week, he recovered from epigastralgia with a concomitant improvement in laboratory parameters.[Ref]

Musculoskeletal side effects have included the development of a nonspecific polyarthritis, which appears to resolve after withdrawal of omeprazole. Hip and other bone fractures have been reported. At least one case of acute severe myopathy has also been reported.[Ref]


Immunologic side effects have been reported rarely. These have included a single case report of an autoimmune disorder with the development of fever, arthralgias, Raynaud's phenomenon, and a positive ANA titer.[Ref]


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It is possible that some side effects of omeprazole may not have been reported. These can be reported to the FDA here. Always consult a healthcare professional for medical advice.

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