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Omeprazole: 7 things you should know

Medically reviewed by Carmen Fookes, BPharm. Last updated on Aug 17, 2022.

1. How it works

  • Omeprazole may be used to treat certain stomach conditions by decreasing levels of stomach acid.
  • Omeprazole reduces the production of stomach acid and works by irreversibly blocking the actions of an enzyme responsible for acid production, called H+/K+ ATPase (also known as the gastric proton pump). The proton pump is located in the parietal cells of the stomach wall. Both baseline gastric acid secretion and stimulated gastric acid secretion are affected; the degree that they are affected depends upon the dose of omeprazole.
  • This allows damaged tissue in the esophagus, stomach, and duodenum to heal, and reduces the risk of new ulcers from forming. PPIs are also used to treat other gastrointestinal disorders characterized by excessive acid secretion.
  • Omeprazole belongs to the class of medicines known as proton pump inhibitors (PPIs).

2. Upsides

  • May be considered for the short-term treatment of gastroesophageal reflux disease (GERD) (also known as heartburn) and erosive esophagitis (a severe inflammation of the lining of the esophagus - the tube that carries food from the mouth to the stomach).
  • May be used in addition to antibiotics to eradicate Helicobacter pylori (a bacteria found in the gut that is linked to gastric ulcers).
  • Can be used for the short-term treatment of active duodenal ulcer in adults. Most people heal within 4 weeks.
  • Useful in the treatment of hypersecretory conditions such as Zollinger-Ellison syndrome.
  • Usually only up to 4 weeks of treatment is required; however, some people may require an additional 4 weeks.
  • Omeprazole may also be used to maintain the healing of erosive esophagitis.
  • No dosage adjustment is needed in people with kidney disease; however, a dosage reduction should be considered in those with liver disease, particularly when omeprazole is used to heal erosive esophagitis.
  • Omeprazole is available as a tablet and capsule formulation in various strengths and also as an oral suspension.
  • Generic omeprazole is available.

3. Downsides

If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:

  • Diarrhea, a headache, drowsiness, abdominal pain, nausea or vomiting, or tongue discoloration. May also interfere with some laboratory tests.
  • Taste disturbances have also been reported but these usually resolve on discontinuation of therapy.
  • Prolonged treatment (greater than 24-36 months) may cause vitamin B12 deficiency. The risk is greater in women, people younger than 30, and with higher dosages.
  • PPIs (including omeprazole) have been associated with an increased risk of osteoporosis-related fractures of the hip, wrist, or spine. People on high-dose or long-term therapy are more at risk.
  • Has also been associated with other conditions such as lupus erythematosus and magnesium deficiency.
  • Administration of PPIs (such as omeprazole) has been associated with acute interstitial nephritis, a severe inflammation of the kidneys. May occur on medication initiation or at any point of therapy. Symptoms include fever, rash and generalized aches and pains. Discontinue omeprazole and seek medical advice.
  • Has been associated with a greater risk of Clostridium difficile-associated diarrhea. See your doctor if you develop diarrhea that does not improve.
  • May interact with some other medications including methotrexate and sometimes warfarin. Omeprazole can also reduce the absorption of drugs that are dependant on a certain gastric pH for their absorption. It may also interact with drugs metabolized through the cytochrome P450 pathway (particularly CYP2C19 and CYP3A4).
  • Some studies have suggested PPIs (such as omeprazole) are associated with a higher risk of stomach cancer and kidney disease.
  • There are no adequate or well-controlled studies of omeprazole during pregnancy but animal studies have shown changes in bone morphology in offspring of rats dosed throughout pregnancy and lactation. Use only if potential benefits justify the risk. It is unknown how omeprazole affects a breastfeeding infant.

Note: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. View complete list of side effects

4. Bottom Line

  • Omeprazole decreases stomach acid production which promotes the healing of gastric and duodenal ulcers and other inflamed areas of gastrointestinal tissue. The risk of interactions with omeprazole is greater than with other PPIs such as lansoprazole and pantoprazole. Omeprazole is best used short-term.

5. Tips

  • Usually taken once daily; however, take as directed by your doctor.
  • Use the lowest dose for the shortest amount of time appropriate to the condition being treated.
  • Administer on an empty stomach at least one hour before a meal.
  • Do not crush or chew tablets or capsules. Swallow whole.
  • Capsules can be opened and the contents mixed with applesauce and swallowed immediately in patients who have difficulty swallowing capsules. Do not heat, chew, or store the applesauce for later.
  • A commercially prepared suspension is available. A pharmacist can also make one.
  • See your doctor if you develop any unexplained fever, rash (particularly one that gets worse after you have been in the sun), new or worsening joint pain, persistent diarrhea, or generalized aches and pains.
  • Also see your doctor if you develop any muscle cramps, spasms, or weakness; jitteriness; abnormal heartbeat; dizziness; seizures; or any other symptoms of concern.
  • Tell your doctor if you are breastfeeding, pregnant, or intending to become pregnant because omeprazole may not be suitable for you.

6. Response and effectiveness

  • Acid-suppressing effects occur within an hour of dosing, with the maximal effect occurring within 2 hours. Effects last for up to 72 hours.
  • Acid levels return to previous levels within 3 to 5 days of discontinuation.

7. Interactions

Medicines that interact with omeprazole may either decrease its effect, affect how long it works for, increase side effects, or have less of an effect when taken with omeprazole. An interaction between two medications does not always mean that you must stop taking one of the medications; however, sometimes it does. Speak to your doctor about how drug interactions should be managed.

Common medications that may interact with omeprazole include:

  • aminophylline or theophylline
  • amphetamine
  • ampicillin
  • astemizole
  • bisphosphonates, such as alendronate, etidronate, or risedronate
  • capecitabine
  • cefuroxime
  • citalopram
  • clopidogrel
  • clozapine
  • cyclosporine
  • CYP2C19 inducers such as enzalutamide, rifampin, tocilizumab, or St John's Wort
  • CYP2C19 inhibitors such as amitriptyline, clomipramine, fluconazole or ticlopidine
  • delavirdine
  • digoxin
  • diuretics
  • doxycycline
  • HIV medications (eg, atazanavir, indinavir, ritonavir, or saquinavir)
  • iron supplements
  • mesalamine
  • methotrexate
  • methylphenidate
  • medications that rely on a certain gastric pH for absorption, such as ampicillin, bisacodyl, dasatinib, erlotinib, iron salts, ketoconazole/itraconazole, mycophenolate mofetil, or nilotinib
  • moclobemide
  • multivitamins that contain vitamins A, D, E, or K; folate; or iron
  • sucralfate
  • tacrolimus
  • tumor necrosis factor inhibitors such as adalimumab, etanercept, or infliximab
  • warfarin.

In addition, omeprazole may affect some diagnostic tests, for example, those for neuroendocrine tumors or the secretin stimulation test. There have also been reports of false-positive urine screening tests for tetrahydrocannabinol (THC) in patients receiving PPIs, such as omeprazole.

Note that this list is not all-inclusive and includes only common medications that may interact with omeprazole. You should refer to the prescribing information for omeprazole for a complete list of interactions.


Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use omeprazole only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Copyright 1996-2023 Revision date: August 16, 2022.