Omeprazole: everything you need to know

Mike Bohl, MD, MPH, ALM - Contributor Avatar

Written by Chimene Richa, MD 

Mike Bohl, MD, MPH, ALM - Contributor Avatar

Written by Chimene Richa, MD 

last updated: Aug 11, 2020

5 min read

Omeprazole (brand name Prilosec or Prilosec OTC) is a medication used to treat conditions due to increased stomach acid, like heartburn and stomach ulcers. It is available both over the counter (OTC) and by prescription. Omeprazole is part of the proton pump inhibitor (PPI) class of drugs, which also includes esomeprazole, lansoprazole, and pantoprazole.

Proton pump inhibitors act on specialized pumps—called proton pumps—in stomach cells responsible for producing stomach acid (DailyMed, 2017). By inhibiting proton pumps, omeprazole decreases the amount of acid that the stomach makes, improving symptoms.


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Uses for omeprazole

Omeprazole helps decrease the amount of acid in the stomach, improving conditions caused or worsened by high stomach acid levels. These include (DailyMed, 2017):

  • Duodenal ulcers & gastric ulcers (peptic ulcer disease, or PUD)

  • Gastroesophageal reflux disease (GERD)

  • Heartburn

  • Zollinger-Ellison syndrome

Duodenal and gastric ulcers

Sores in your stomach (gastric ulcers) or small intestine (duodenal ulcers) are signs of peptic ulcer disease (PUD). PUD is most frequently caused by either a stomach infection from Helicobacter pylori (H. pylori) bacteria or from taking too many non-steroidal anti-inflammatory drugs (NSAIDs), like ibuprofen or naproxen (Vakil, 2020). 

The most common symptom of peptic ulcers is intermittent attacks of stomach pain. As you can imagine, stomach acid hitting the ulcers in your stomach or intestine is not always a comfortable sensation. Omeprazole can help treat your peptic ulcers by decreasing your stomach acid production and improving symptoms. It is often combined with antibiotics (like clarithromycin and amoxicillin) to treat the H. pylori stomach infections.

Gastroesophageal reflux disease (GERD)

GERD is often called “acid reflux” because stomach acid flows backward up the esophagus, causing uncomfortable heartburn symptoms. It’s normal to have occasional episodes of reflux. However, if you find that you are experiencing frequent symptoms, you may have GERD. Common symptoms of GERD include heartburn, regurgitation (food rising in the back of your throat), a sour taste in your mouth, and cough (Kahrilas, 2020).

Acid reflux/GERD does more than just make you feel uncomfortable. It can damage your esophagus (the tube that connects your mouth to your stomach). Some people go on to develop Barrett’s esophagus, a condition in which the lining of the esophagus becomes red and thickened from the frequent exposure to stomach acid. Barrett’s esophagus may increase your risk of getting esophageal cancer. GERD can also lead to sores and erosions in your esophagus called erosive esophagitis (Kahrilas, 2020).

Using PPIs like omeprazole can decrease your stomach acid production and help improve both your symptoms and the damage to your esophagus.

OC Omeprazole: everything you need to know image edb7006a-1de5-4d35-9068-ebef05feffe8


You may occasionally experience episodes of heartburn, especially after meals. These generally do not last long and are usually not a cause for concern. Taking omeprazole during these episodes can help decrease your stomach acid. However, if your heartburn becomes more frequent and uncomfortable, talk to your healthcare provider as you may need additional testing.

Zollinger-Ellison syndrome

In ZES, a rare condition, abnormal growths (gastrinomas) in the pancreas or the upper part of the small intestine release a substance called gastrin. Gastrin is a hormone that tells the stomach to secrete more acid. People with ZES produce so much acid that they often develop PUD and heartburn. Omeprazole can help decrease stomach acid production.

What is the dose of omeprazole?

Most people take omeprazole in the oral delayed-release capsule or tablet form. These pills should be swallowed whole (do not chew or crush) and should be taken 30–60 minutes before a meal—ideally breakfast (UpToDate, n.d.). Omeprazole capsules or tablets are available over-the-counter in 10 mg and 20 mg pills and by prescription in 40 mg pills. 

If you have difficulty swallowing pills, you can add the contents of the omeprazole delayed-release capsule to applesauce and swallow the applesauce without chewing it. Do not store the omeprazole/applesauce mixture for future use (UpToDate, n.d.). It is also available as an oral suspension.

What are the side effects of omeprazole?

Some of the more common side effects of omeprazole include (UpToDate, n.d.):

  • Headaches

  • Abdominal pain

  • Diarrhea or constipation

  • Nausea/vomiting

  • Flatulence (gas)

  • Dizziness

If you take omeprazole with antibiotics (like amoxicillin), there is an increased risk of having serious side effects. Rarely, people may experience anaphylaxis or a severe allergic reaction to the drug combination, especially if they already had a penicillin allergy. Also, the risk of developing a Clostridium difficile (C. diff) infection increases when using both PPIs and amoxicillin (DailyMed, n.d.).

Rarely, people who use PPIs long-term (over one year) develop fundic gland polyps, which are small masses in the upper part of the stomach. These polyps are not cancerous and often resolve after stopping the medication (DailyMed, n.d.). Another concern of long-term PPI use is the increased risk of osteoporosis-related bone fractures of the hip, wrist, or spine (UpToDate, n.d.). Consider calcium and vitamin D supplementation if you will be taking omeprazole for longer than three months.

Long-term use of PPIs may also cause low magnesium (hypomagnesemia). Hypomagnesemia may have no symptoms or, at its worst, it may cause muscle rigidity (tetany), seizures, and abnormalities of heart rhythms (cardiac arrhythmias) (UpToDate, n.d.). Again, stopping the medication restores the magnesium levels.

Some people who take omeprazole develop an allergic reaction that affects their kidneys—a condition called interstitial nephritis. Fortunately, this gets better after stopping the PPI. Using omeprazole for more than three years may decrease the absorption of vitamin B12, especially in women under 30, and lead to a vitamin B12 deficiency (UpToDate, n.d.). Certain autoimmune diseases, like cutaneous lupus erythematosus (CLE) or systemic lupus erythematosus (SLE), can get worse with PPIs (UpToDate, n.d.).

This list does not include all possible side effects and others may occur. Check with your pharmacist or healthcare provider for more information.

Drug interactions with omeprazole

Before starting any medicines, be sure to seek medical advice to discuss any potential drug interactions. Some medications that may interact with omeprazole include:

  • Clopidogrel (brand name Plavix): Taking PPIs with clopidogrel (a blood thinner) can decrease the effectiveness of clopidogrel (UpToDate, n.d.). 

  • Drugs metabolized by the liver: Medications broken down by the cytochrome P450 system in the liver (like warfarin, phenytoin, and diazepam) may be affected by PPIs, making them stay in your bloodstream for longer (DailyMed, n.d.).

  • Voriconazole: Voriconazole can more than double the amount of omeprazole in your body if you take this antifungal drug with PPIs (DailyMed, n.d.).

  • Atazanavir (brand name Reyataz): Taking atazanavir (HIV antiviral drug) along with PPIs decreases the levels of atazanavir, making it less effective at fighting off the HIV infection (DailyMed, n.d.). Nelfinavir is another antiviral drug that may be affected by omeprazole.

  • Tacrolimus: PPIs may increase the amount of tacrolimus (a drug for transplant recipients to prevent graft rejection) in your bloodstream (DailyMed, n.d.).

This list does not include all possible drug interactions with omeprazole and others may exist. Check with your pharmacist or healthcare provider for more information.

Who should not use omeprazole?

Certain groups of people should avoid using omeprazole or may need a reduced dose—these special populations include:

  • Pregnant women: Omeprazole is pregnancy category C. This means there is not enough information to determine the risk to the pregnancy (DailyMed, n.d.). Women and their healthcare providers should weigh the benefits of omeprazole against the risk to the fetus.

  • Nursing mothers: Omeprazole does get into the breastmilk, but no adverse effects have been reported. Women and their healthcare providers should weigh the risks and benefits of taking the medication (DailyMed, n.d.).

  • People with liver disease: Since the liver breaks down omeprazole, people with liver disease may have higher than expected levels of the drug in their system. They may need a lower dose of omeprazole (UpToDate, n.d.).

  • People of Asian descent: Asian populations, especially those being treated for erosive esophagitis, may need a lower dose to prevent side effects (UpToDate, n.d.).

This list does not include all at-risk groups. Talk to your healthcare provider or pharmacist for more information.


If you have any medical questions or concerns, please talk to your healthcare provider. The articles on Health Guide are underpinned by peer-reviewed research and information drawn from medical societies and governmental agencies. However, they are not a substitute for professional medical advice, diagnosis, or treatment.

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Every article on Health Guide goes through rigorous fact-checking by our team of medical reviewers. Our reviewers are trained medical professionals who ensure each article contains the most up-to-date information, and that medical details have been correctly interpreted by the writer.

Current version

August 11, 2020

Written by

Chimene Richa, MD

Fact checked by

Mike Bohl, MD, MPH, ALM

About the medical reviewer

Dr. Mike is a licensed physician and a former Director, Medical Content & Education at Ro.