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8 Uses of Omeprazole (Prilosec) & Side Effects

Written by Mathew Eng, PharmD | Last updated:
Jonathan Ritter
Puya Yazdi
Medically reviewed by
Jonathan Ritter, PharmD, PhD (Pharmacology), Puya Yazdi, MD | Written by Mathew Eng, PharmD | Last updated:

Omeprazole is available by prescription and is also sold over-the-counter for stomach disorders. It is used for several conditions, including heartburn, indigestion, and stomach ulcers. Read on to learn more about how omeprazole works, its other uses and its side effects.

What Is Omeprazole?

Omeprazole (brand name Prilosec, Zegerid, or Losec) is a medication used to reduce the release of acid in the stomach. Stomach acid helps break down proteins from food, but too much stomach acid can cause problems, like ulcers and heartburn [1].

Omeprazole is available both over-the-counter and as a prescription drug. Over-the-counter omeprazole is only intended for frequent heartburn [2].

Prescription doses of omeprazole may be higher than over-the-counter doses and typically are used to treat more severe conditions, such as stomach ulcers and Zollinger-Ellison syndrome [3].

Mechanism of Action

Omeprazole belongs to a class of drugs called proton pump inhibitors (PPIs).

PPIs, such as omeprazole, reduce acid release in the stomach by blocking hydrogen-potassium ATPase, which is an enzyme that increases acid levels. By reducing the release of acid, omeprazole can help treat various stomach disorders such as ulcers and heartburn [4].

Research also shows that omeprazole may increase superoxide dismutase and aquaporin-4 in the stomach (mucosal cells). Superoxide dismutase is an important antioxidant enzyme, and aquaporin-4 is a molecule that helps maintain water balance in cells [5, 6].

Uses of Omeprazole

Over-the-Counter Uses

When taking over-the-counter medications, always carefully read the directions, warnings, and side effects. Consult your doctor or pharmacist if you have any questions.

1) Heartburn

Heartburn occurs when acid in the stomach travels up into the esophagus, causing a burning sensation. Over-the-counter omeprazole is only intended for the treatment of frequent heartburn. According to the FDA, frequent heartburn is defined as heartburn that occurs 2 or more days a week.

A number of clinical trials have found that 20 mg of omeprazole (the over-the-counter strength) each day for 14 days can reduce the symptoms of heartburn.

For example, two randomized placebo-controlled trials (with 331 and 320 patients) found that over-the-counter omeprazole significantly reduces heartburn after a 14-day regimen [7].

Prescription Uses


Gastroesophageal reflux disease (GERD), also referred to as acid reflux, is a chronic condition where contents inside the stomach rise up into the esophagus, which can cause heartburn, pain, regurgitation, and other complications.

A randomized placebo-controlled trial of 355 patients with GERD found that omeprazole may reduce symptoms of heartburn, regurgitation, nausea, pain, and difficulty swallowing [8].

Another randomized trial of 216 patients with mild GERD suggests that taking omeprazole on a daily basis reduces the return of symptoms better compared to taking the medication as needed [9].

A meta-analysis of patients with erosive GERD found that omeprazole may reduce symptoms better than H2 blockers or antacids. According to the researchers, omeprazole is more cost-effective and may be the best option for patients with GERD who did not respond to other treatments [10].

A long-term study of 240 patients with GERD examined the safety and effectiveness of omeprazole for up to 11 years of use. The researchers concluded that long-term use of omeprazole is effective and safe for the treatment of GERD [11].

3) Indigestion

Indigestion, also known as dyspepsia, is characterized by symptoms such as bloating, fullness, heartburn, belching, and pain [12].

A randomized controlled trial of 471 patients with indigestion found that omeprazole reduced pain at nighttime, especially in those with a high BMI [13].

In a randomized placebo-controlled trial of 1,262 patients with indigestion, omeprazole showed only a modest benefit over placebo [14].

Another randomized placebo-controlled trial looked at 829 patients with indigestion and found that omeprazole may reduce symptoms of pain, discomfort, bloating, and nausea better than placebo. The patients who received omeprazole also returned to the doctor less often over the following year [15].

4) Zollinger-Ellison Syndrome

Zollinger-Ellison syndrome is a disorder in which the stomach produces too much acid because of either a tumor or enlargement of the pancreas, which can lead to the development of ulcers [16].

In a 9-year long study of 116 patients, researchers concluded that omeprazole is safe and effective for reducing the high levels of stomach acid in those with Zollinger-Ellison syndrome [17].

Other studies suggest that the omeprazole dose may be gradually lowered once stomach acid levels are adequately controlled [18, 19].

5) Gut Bleeding

A randomized placebo-controlled trial of 220 patients with gut ulcers and signs of recent bleeding found that omeprazole significantly reduces recurrent bleeding and recurrent surgery compared to placebo (but not in those with arterial sprouting or oozing) [20].

Another randomized placebo-controlled trial of 149 patients with a high-risk peptic ulcer suggests that omeprazole may decrease the duration of hospital stay (average 11.3 hours less than placebo), rebleeding, and the need for blood transfusions [21].

A meta-analysis of 10 clinical trials including 1,283 patients with bleeding in the stomach found that omeprazole may be more effective at preventing rebleeding than H2 blockers [22].

6) NSAID Protection

NSAIDs, which are common anti-inflammatory drugs (aspirin, ibuprofen, naproxen, etc.), increase the risk of peptic ulcers. Omeprazole is sometimes prescribed along with NSAIDs to reduce acid levels and protect the stomach [23, 24].

A randomized controlled trial 156 patients with ulcers and who were receiving long-term NSAID treatment found that omeprazole may be safe and effective for the treatment of NSAID-induced ulcers [25].

In a randomized controlled trial of 935 patients who required long-term NSAID treatment, omeprazole reduced ulcers, pain, and heartburn [26].

Another randomized controlled trial of 541 patients taking NSAIDs over a prolonged period of time found that omeprazole may heal and prevent ulcers more effectively than ranitidine, another type of medication used to reduce stomach acid [27].

7) H. pylori Infections

H. pylori is a type of bacteria that is commonly found in the stomach. While it does not always lead to symptoms, it can sometimes cause ulcers and lead to stomach cancer [28].

Omeprazole given with antibiotics (amoxicillin, clarithromycin, or metronidazole), also known as triple therapy, is used to eradicate H. pylori. This same treatment also seems to be effective for children with H. pylori [29, 30].

A meta-analysis of 89 patients with H. pylori found that omeprazole given along with 2 antibiotics (clarithromycin and metronidazole) may eradicate H. pylori in 85 to 95% of patients [31].

8) Peptic Ulcers

In an open-label study of 30 patients with ulcers that did not respond to other anti-ulcer medications, omeprazole treatment healed peptic ulcers in 29 out of 30 patients [32].

A multicenter trial including more than 600 patients with stomach ulcers found that omeprazole may be more effective at healing ulcers than ranitidine, an H2 blocker [33].

Safety of Omeprazole

Side Effects

Omeprazole can cause several side effects. If any side effects persist or worsen, let your doctor know. This is also not a complete list of possible side effects. Tell your doctor if you experience any serious side effects or notice any effects not listed here.

Some common side effects include [34]:

  • Headache
  • Abdominal pain
  • Nausea
  • Diarrhea
  • Vomiting
  • Flatulence

Some serious side effects include [34]:

  • Blood or mucus in the stool
  • Persistent diarrhea
  • Irregular heartbeat
  • Persistent muscle spasms


Clostridium difficile Associated Diarrhea

Clostridium difficile is a type of bacteria that can cause severe infection. Omeprazole use may be associated with this type of infection. Patients taking omeprazole should be aware of the signs and symptoms of Clostridium difficile, which includes persistent diarrhea and blood or mucus in the stool [35].

Bone Fractures

Long-term use of omeprazole has been associated with an increased risk of osteoporosis-related fractures [35].


Those who are allergic or hypersensitive to omeprazole or any of its components should not take this medication [34].

Pregnancy and Breastfeeding

There is some evidence that omeprazole is safe for use during pregnancy, but clinical research is limited. If you are pregnant or plan to become pregnant, talk to your doctor before using omeprazole [34, 36].

There is also some evidence that omeprazole may be excreted in breast milk. A doctor will weigh the benefits and risks when determining if the use of omeprazole is appropriate during breastfeeding [34].

Drug Interactions

The following drugs have been reported to interact with omeprazole. However, this is not a complete list, let your doctor know of all the medications you are currently taking to avoid any unexpected interactions.

  • Atazanavir
  • Nelfinavir
  • Tacrolimus
  • Saquinavir
  • Voriconazole
  • Warfarin
  • Diazepam
  • Phenytoin
  • Cyclosporine
  • Ketoconazole
  • Clopidogrel
  • Methotrexate

Forms and Dosage of Omeprazole

The dosing of omeprazole can vary. Always take this medication as directed by a doctor.

Omeprazole is available in immediate and delayed-release tablets, capsules, orally disintegrating tablets (ODTs), and oral suspensions.

Over-the-counter omeprazole is available as a 20 mg delayed-release tablet, which should be taken once a day for up to 14 days.

Prescription doses of omeprazole can vary depending on the condition being treated.

About the Author

Mathew Eng

Mathew Eng

Mathew received his PharmD from the University of Hawaii and an undergraduate degree in Biology from the University of Washington.
Mathew is a licensed pharmacist with clinical experience in oncology, infectious disease, and diabetes management. He has a passion for personalized patient care and believes that education is essential to living a healthy life. His goal is to motivate individuals to find ways to manage their chronic conditions.


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