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 Omeprazole. If you are concerned about side effects, discuss the risks and benefits of Omeprazole with your doctor.

The following side effects have been reported by at least 1% of people taking Omeprazole. 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
• Constipation
• Diarrhea or loose stools
• dizziness
• Dry Mouth
• gas
• headache
• 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:

• blurred vision
• diarrhea (watery and severe; may also be bloody)
• 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 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)

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 Omeprazole.

Each capsule with opaque pink body and opaque reddish-brown cap, printed "APO 020", contains 20 mg of omeprazole. Nonmedicinal ingredients: eudragit, magnesium hydroxide, mannitol, povidone, and triethyl citrate; capsule shell: gelatin, red iron oxide, and titanium dioxide; black ink: pharmaceutical shellac, ethyl alcohol, isopropyl alcohol, b-butyl alcohol, propylene glycol, ammonium hydroxide, and black iron oxide; may contain: potassium hydroxide, D&C Yellow No. 10 Aluminum Lake, FD&C Blue No. 1 Aluminum Lake, FD&C Blue No. 2 Aluminum Lake, or FD&C Red No. 40 Aluminum Lake.

Do not take Omeprazole if you:

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

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 Omeprazole. 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.

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 Omeprazole.

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 Omeprazole. 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 Omeprazole.

Liver function: Liver disease or reduced liver function may cause Omeprazole to build up in the body. If you have liver problems, discuss with your doctor how Omeprazole may affect your medical condition, how your medical condition may affect the dosing and effectiveness of Omeprazole, and whether any special monitoring is needed. Your doctor may want to test your liver function regularly with blood tests while you are taking Omeprazole. 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 two 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 Omeprazole may affect your medical condition, how your medical condition may affect the dosing and effectiveness of Omeprazole, 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 increase risk of fractures, particularly for people who take Omeprazole for a year or longer. The lowest dose of Omeprazole 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: Omeprazole should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking Omeprazole, call your doctor immediately.

Breast-feeding: Omeprazole passes into breast milk. If you are a breast-feeding mother 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 Omeprazole have not been established for children.

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 GERD (Gastroesophageal reflux disease) (GERD).

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

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

Your doctor may have suggested Omeprazole 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 Omeprazole, speak to your doctor. Do not stop taking Omeprazole without consulting your doctor.

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