Omeprazole belongs to the family of medications called proton pump inhibitors (PPIs). It slows or prevents the production of acid within the stomach.

Omeprazole is used to treat conditions where reduction in acid secretion is required for proper healing, including stomach and intestinal ulcers (gastric and duodenal ulcers), the prevention and treatment of ulcers associated with medications known as NSAIDs, reflux esophagitis, Zollinger-Ellison syndrome, heartburn, and gastroesophageal reflux disease (GERD).

It is also used in combination with antibiotics to treat stomach ulcers caused by H. pylori bacteria.

This medication may be available under multiple brand names and/or in several different forms. Any specific brand name of this medication may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of this medication may not be used for all of the conditions discussed here.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

The usual recommended dose of omeprazole is 10 mg to 40 mg once daily. The dose and length of treatment depends on the condition being treated. This medication can be taken with or without food and should be swallowed whole with water.

When used to treat ulcers in the duodenum, the recommended adult dose is 20 mg taken once daily for 2 to 4 weeks.

To treat ulcers in the stomach, reflux esophagitis, and ulcers associated with the use of NSAIDs, the recommended adult dose is 20 mg taken once daily for 4 to 8 weeks.

For treatment of heartburn, the recommended adult dose is 20 mg daily.

When used to treat stomach ulcers caused by H. pylori in adults, the dose of omeprazole is 20 mg taken 2 times daily with 1,000 mg of amoxicillin 2 times daily and 500 mg of clarithromycin 2 times daily, all for 7 days. Another dosing regimen for H. pylori infections is 20 mg of omeprazole, 500 mg of metronidazole, and 250 mg of clarithromycin, all twice daily for 7 days.

If your ulcer continues to bother you, your doctor may suggest that you continue taking omeprazole for a period of time to make sure that your ulcer is fully healed.

When treating Zollinger-Ellison syndrome, the dose of omeprazole varies, but is often higher than the doses used to treat ulcers. Doses larger than 80 mg daily are often needed.

Many things can affect the dose of a medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones listed here, do not change the way that you are taking the medication without consulting your doctor.

It is important to take this medication exactly as prescribed by your doctor. If you miss a dose, take it as soon as possible and continue with your regular schedule. If it is less than 12 hours until your next dose, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

Store this medication at room temperature, protect it from moisture, and keep it out of the reach of children.

Each red-brown, circular, biconvex, enteric-coated tablet printed "OM20" on one side contains 20.6 mg of omeprazole magnesium, equivalent to 20 mg of omeprazole. Nonmedicinal ingredients: mannitol, microcrystalline cellulose, sodium starch glycolate, hydroxypropyl methylcellulose, talc, sodium stearyl fumarate, methacrylic acid copolymer, polyethylene glycol, titanium dioxide, red iron oxide, and yellow iron oxide; imprinting ink: shellac, isopropyl alcohol, iron oxide black, N-butyl alcohol, propylene glycol, and ammonium hydroxide.

Do not take this medication if you:

• are allergic to omeprazole or any ingredients of this medication
• are taking the medication rilpivirine

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

• abdominal or stomach pain
• altered sense of taste
• constipation
• diarrhea or loose stools
• dizziness
• dry mouth
• gas
• hair loss
• headache
• increased sweating
• muscle weakness
• nausea
• sensation of spinning
• sleepiness
• trouble sleeping
• vomiting

Although most of these side effects listed below don't happen very often, they could lead to serious problems if you do not seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

• agitation
• aggressive behaviour or hostility
• anxiety
• blurred vision
• breast development (in men)
• diarrhea (watery and severe; may also be bloody)
• confusion
• hallucination
• increased sensitivity to sunlight
• joint pain
• mild skin rash or itching
• mouth inflammation
• muscle aches or cramps
• pain or burning in the mouth or throat
• rash on cheeks or arms that gets worse in the sun
• sensation of burning, prickling, or numbness
• signs of electrolyte imbalance (e.g., muscle pain or cramps, weakness, irregular heartbeat, lack of coordination, thirst, confusion)
• signs of kidney problems (e.g., blood in the urine, decreased urine production)
• signs of liver damage (yellow skin or eyes, dark urine, loss of appetite, abdominal pain, fever, and fatigue)
• symptoms of low sodium levels in the blood (e.g., achy, stiff or uncoordinated muscles, confusion, tiredness, weakness)

Stop taking the medication and seek immediate medical attention if any of the following occur:

• signs of an allergic reaction (e.g., difficulty breathing, hives, swelling of the face or throat)
• signs of bleeding in the stomach (e.g., bloody, black, or tarry stools; spitting up of blood; vomiting blood or material that looks like coffee grounds)
• signs of a severe skin reaction such as blistering, peeling, a rash covering a large area of the body, a rash that spreads quickly, or a rash combined with fever or discomfort

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Before you begin using a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use this medication.

Diarrhea: When gastric acid is decreased, the number of bacteria normally in the digestive system increases. Occasionally, this can cause serious infection in the digestive tract. If you experience watery, foul-smelling bowel movements after starting to take omeprazole, contact your doctor as soon as possible.

Fluid and electrolyte balance: Omeprazole, like other PPIs, may cause the levels of electrolytes such as potassium, sodium, magnesium, chloride, and calcium in the blood to change while taking this medication. If you experience symptoms of fluid and electrolyte imbalance such as muscle pains or cramps; dry mouth; numb hands, feet, or lips; or racing heartbeat, contact your doctor as soon as possible. Your doctor will do blood tests regularly to monitor the levels of these electrolytes in your blood while you are taking this medication.

Hypersensitivity reactions: Hypersensitivity reactions have been reported with the use of omeprazole. They may include a blistering, severe rash. In rare cases, Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS syndrome) may occur. This reaction involves symptoms including fever, swollen glands, yellowing of the skin or eyes, flu-like symptoms with skin rash or blistering, or other organ involvement. These reactions are medical emergencies. Get immediate medical attention if you have symptoms of a severe allergic reaction. If you experience any unusual symptoms, contact your doctor.

Liver function: Liver disease or reduced liver function may cause this medication to build up in the body. If you have liver problems, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed. Your doctor may want to test your liver function regularly with blood tests while you are taking this medication. People with severe liver disease should generally not take more than 20 mg of omeprazole daily.

Methotrexate interaction: Omeprazole, like other medications in this group, may interact with methotrexate when the 2 medications are used at the same time. This combination may lead to higher-than-expected amounts of methotrexate in the body and can cause serious side effects, including kidney damage, irregular heartbeat, anemia, or infection. If you take omeprazole and are also going to receive a dose of methotrexate, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Osteoporosis-related fractures: Studies suggest that the use of omeprazole, like other PPIs, may be related to an increased risk of fractures, particularly for people who take this medication for a year or longer. The lowest dose of this medication to control the symptoms, taken for the shortest period of time is less likely to cause these problems.

Severe stomach problems: If you have recurrent vomiting, difficulty swallowing, blood in the stool, coughing up of blood, or significant unintentional weight loss, check with your doctor immediately. These symptoms may be signs of a more serious stomach problem.

Subacute cutaneous lupus erythematosus (SCLE): Omeprazole, like other PPIs, has been rarely associated with SCLE, an autoimmune disease.  If you develop any skin lesions, especially in sun-exposed skin areas, and if accompanied by muscle aches or pains, contact your doctor immediately.

Vitamin B12: Long-term use of omeprazole may lead to vitamin B12 deficiency. If you are a vegetarian or have low vitamin B12 levels, discuss with your doctor whether any special monitoring is required.

Pregnancy: This medication should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking this medication, call your doctor immediately.

Breast-feeding: This medication passes into breast milk. If you are breast-feeding and are taking omeprazole, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: The safety and effectiveness of using this medication have not been established for children.

There may be an interaction between omeprazole and any of the following:

• amphetamines (e.g., dextroamphetamine, lisdexamfetamine)
• apalutamide
• "azole" antifungals (e.g., itraconazole, ketoconazole, voriconazole)
• bisphosphonates (e.g., alendronate, etidronate, risedronate)
• bosentan
• cannabis
• capecitabine
• cefuroxime
• clobazam
• clopidogrel
• clozapine
• cyclosporine
• dabigatran
• dexmethylphenidate
• digoxin
• doxycycline
• elagolix
• enzalutamide
• hepatitis C antivirals (e.g., dasabuvir, ledipasvir, ombitasvir, paritaprevir, ritonavir, velpatasvir)
• HIV protease inhibitors (e.g., atazanavir, indinavir, ritonavir, saquinavir)
• iron salts (e.g., ferrous fumarate, ferrous sulphate)
• lumacaftor
• mesalamine
• methotrexate
• methylphenidate
• multivitamins with iron, folate
• mycophenolate
• pazopanib
• phenytoin
• protein kinase inhibitors (e.g., bosutinib, dasatinib, nilotinib, pazopanib)
• raltegravir
• rifampin
• rilpivirine
• riociguat
• St. John's wort
• SSRI antidepressants (e.g., citalopram, escitalopram, fluoxetine, fluvoxamine)
• tacrolimus
• warfarin

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.