What to Know About Prilosec (Omeprazole)

A Treatment for Acid Reflux, Ulcers, and Esophagitis

Prilosec tablets

Verywell / Anastasia Tretiak

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Prilosec (omeprazole) is a proton-pump inhibitor (PPI) used to help treat heartburn symptoms, ulcers, gastroesophageal reflux disease (GERD), and erosive esophagitis. Prilosec blocks an enzyme that allows acid to be released from proton pumps in gastric cells (a type of stomach cell). This prevents too much acid from harming the tissues lining your esophagus, stomach, and intestines.

Prescription Prilosec is for diseases that require diagnosis and monitoring by a healthcare provider, while over the counter (OTC) Prilosec is only used to treat heartburn. There are generic versions of both of these medications.

Prescription Prilosec comes in delayed-release capsules and an oral suspension that you mix with water and drink. Prilosec OTC comes in delayed-release tablets.


Prilosec OTC is used to treat heartburn. It is approved for adults ages 18 and up.

Prescription Prilosec is also used for heartburn and is a standard treatment for GERD, gastric ulcers (ulcers of the stomach lining), and duodenal ulcers (located in the duodenum of the small intestine). In addition, prescription Prilosec can be used to help heal erosive esophagitis or to treat Helicobacter pylori (H. pylori, a common ulcer-causing bacteria) as a combination therapy with antibiotics.

Prescription Prilosec can also be used in the management of rare hypersecretory conditions, such as Zollinger-Ellison syndrome, multiple endocrine adenomas, and systemic mastocytosis. In each of these conditions, tumors or cell groupings can produce excess gastric acid.

Prescription Prilosec is approved for use in children age 1 year and older who have GERD or erosive esophagitis. For all of its other approved uses, it is approved for people age 17 and up

It's important to note that you can experience relief from your symptoms while taking Prilosec even if you have a serious condition that needs evaluation and treatment. Be sure to see your healthcare provider.

Before Taking

Prilosec OTC is not an effective treatment for acute symptoms of heartburn (those affecting you right now). It is used daily for two weeks and takes one to four days to take full effect.

Consult your healthcare provider before taking Prilosec OTC, especially if you've had heartburn for more than three months. This can be a sign of a more serious condition.

Before prescribing Prilosec or recommending Prilosec OTC, your practitioner will take your medical history and may do a blood test to check for H. pylori, or a barium-swallow X-ray or other imaging to look for ulcers.

An endoscopy, a procedure in which a thin tube with a light and camera is inserted down your throat to view your upper digestive system, may also be recommended if there is a concern about your esophagus. This inside view can help identify ulcers or erosive esophagitis, tumors, and other esophageal conditions.

An ambulatory acid (pH) monitoring exam is an outpatient procedure in which a tube is inserted into your esophagus for 24 hours to measure acid. And esophageal manometry is a diagnostic procedure in which a tube is inserted to measure muscle contractions of the esophagus and to evaluate the action of your sphincter muscle.

Other PPI medications that are also available by prescription or over the counter include Prevacid (lansoprazole) and Nexium (esomeprazole). Similar prescription-only options include AcipHex (rabeprazole), Protonix (pantoprazole), and Dexilant (dexlansoprazole).

There does not appear to be a significant difference in efficacy in any of the different PPIs on the market.

Several studies show that medications like Prilosec provide better relief and overall healing from acidic damage than H2-blocking medications like Pepcid (famotidine) that decrease stomach acid by blocking histamine-2 (H2) receptors. This is true for both erosive and non-erosive inflammation in your esophagus, stomach, and intestine.

However, your healthcare provider may also recommend an H2-blocker if you have night-time acid reflux that isn't controlled by Prilosec.

Precautions and Contraindications

Certain medical circumstances can make taking Prilosec risky or even prohibit its use. These include:

  • Allergy or hypersensitivity: Severe allergic reactions to Prilosec can happen. If you have a known allergy or hypersensitivity to omeprazole, other PPIs, or substituted benzimidazoles, do not take Prilosec.
  • Black stools or bright red blood in stools: If you have black or bright red in your stools, you should seek medical attention rather than using Prilosec. This can be a sign of gastrointestinal bleeding so it is important for you to be evaluated by a healthcare provider.
  • Pregnancy: There are no adequate and well-controlled studies on the use of omeprazole during pregnancy. While some preliminary studies suggest that taking PPIs during the first trimester does not increase the risk of birth defects or adverse outcomes, you should discuss your options with your healthcare provider if you are pregnant or plan to become pregnant.
  • Nursing: Those who are breastfeeding may need to avoid Prilosec, as it may be transferred to the baby via breastmilk.

Talk to your healthcare provider about all medications, supplements, and vitamins that you currently take. While some drugs pose minor interaction risks, others may outright contraindicate use or prompt careful consideration as to whether the pros of treatment outweigh the cons in your case.


Prilosec OTC comes in 20 milligram (mg) doses that are taken once daily for 14 days. Additional 14-day treatment can be repeated every four months. If this is not enough to relieve symptoms, see your healthcare provider.

Prescription Prilosec comes in capsules that are available in 10, 20, or 40 mg doses. It is also available in oral suspension packets of 2.5 or 10 mg that are added to water. The medication will generally start taking effect in 30 minutes to 3.5 hours.

Usual doses of prescription Prilosec include 20, 40, or 60 mg once a day for adults. However, your healthcare provider may ask you to try 20 mg twice a day if you have symptom relief during the day but experience nighttime acid reflux or if you are taking Prilosec as part of combination therapy for H. pylori.

Usual doses of prescription Prilosec for children are 5, 10, or 20 mg once a day; a practitioner makes a recommendation based on body weight.

It is important that you follow your healthcare provider’s orders on dosing, as more Prilosec does not equal better results.

Dosages for Prescription Prilosec
Treatment Dose Frequency
Duodenal ulcers 20 mg Once daily for four weeks (an additional four weeks is sometimes needed)
Gastric ulcer 40 mg Once daily for four to eight weeks
GERD in adults 20 mg Once daily for four to eight weeks

Erosive esophagitis in adults
20 mg Once daily
GERD or erosive esophagitis in children Dose based on body weight.

11 to 22 lbs: 5 mg 

22 to 44 lbs: 10 mg

44 lbs or more: 20 mg
Once daily 
H. pylori  20 to 40 mg (depends on combination therapy with antibiotics) 40 mg taken once daily or 20 mg taken twice daily
Pathological hypersecretory conditions 60 mg (may vary) Once daily 

All listed dosages are according to the drug manufacturer. Check your prescription and talk to your healthcare provider to make sure you are taking the right dose for you.


Omeprazole has been shown to be twice as potent and to last hours longer in patients with chronic liver disease. Anyone with liver impairment who takes Prilosec, especially if it's as a long-term treatment for erosive esophagitis, may need to take a lower dose.

Elderly patients may clear the drug more slowly from their bodies and may need to take lower dosages.

How to Take and Store

Prilosec OTC should be taken in the morning before eating.

Prescription Prilosec should be taken at least one hour before a meal; preferably before breakfast. Capsules should be swallowed whole and not chewed. If you have swallowing difficulties, the contents of the Prilosec capsule may be mixed into applesauce or a similar soft food. Make sure that the pellets found within the capsule are not crushed or chewed when swallowing.

Store over-the-counter tablets in a dry place at room temperature that's ideally between 68 and 77 degrees F. Store prescription capsules at room temperature that's between 59 to 86 degrees F. Keep the container closed tightly and store it in a dry place that doesn't get a lot of light exposure.

When mixing the oral suspension into water:

  • Use a syringe to measure the liquid. You'll mix 5 milliliters (mL) to each 2.5 mg packet and 15 mL to each 10 mg packet.
  • Stir the medication and the water in a glass and let it sit for two to three minutes to thicken.
  • Stir again and drink within 30 minutes. If it has been longer than that, throw the dose away and prepare a new one.
  • If any medicine remains after drinking, add more water, stir, and drink right away. 

Store the oral suspension at room temperature that's ideally between 68 to 77 degrees F.

If you forget a dose (of either formulation), take it as soon as you remember. If it is almost time for your next dose, skip the missed dose. Do not take a double dose to make up for a missed dose. If you take too much Prilosec, contact your healthcare provider right away.

Side Effects

Prilosec is generally well-tolerated, but there can be some serious side effects and it's important to be aware of them when you begin taking the drug.


The main side effects of Prilosec in adults and children include:

  • Headache
  • Stomach pain
  • Nausea
  • Diarrhea
  • Vomiting
  • Flatulence

In addition to these, there are two additional common side effects in children specifically:

  • Respiratory infections
  • Fever

Tell your healthcare provider if you have any side effect that bothers you or that does not go away over time.


Severe or life-threatening adverse events can happen with proton-pump inhibitors, including allergic reactions or dangerously low magnesium levels. Seek urgent medical attention with any of the following symptoms:

  • Seizures
  • Dizziness
  • Abnormal or fast heart beat
  • Jitteriness
  • Jerking movements or shaking (tremors)
  • Muscle weakness
  • Spasms of the hands and feet
  • Cramps or muscle aches
  • Spasm of the voice box 
  • Rash, hives, or other skin reactions
  • Difficulty breathing
  • Wheezing
  • Difficulty swallowing
  • Unexpected weight loss

Warnings and Interactions

The drug-induced decrease in gastric acidity can interfere with diagnostic tests for neuroendocrine tumors. Always tell your healthcare provider what medications you are taking and especially if you are undergoing any testing.

It is especially important that you tell your healthcare provider if you are taking any of the following medications or supplements, as they can interact with Prilosec. This list is incomplete. Your practitioner or pharmacist can run a check for interactions between your prescribed medications.

  • Antifungal or anti-yeast medications: The potency of either medication may be affected. Omeprazole leads to a higher gastric pH, which may affect how much of the antifungal drug Nizoral (ketoconazole) that your body is able to use, making it less effective. If omeprazole is combined with the antifungal Vfend (voriconazole), it can increase the potency of omeprazole. Dosages may need to be adjusted.
  • Benzodiazepines: Your body's elimination of central nervous system (CNS) depressants, including sedatives and anti-anxiety medications such as Valium (diazepam), can be prolonged when they are taken along with omeprazole. Blood tests may be needed to see if the dosage needs to be adjusted.
  • Synthroid (levothyroxine): PPIs can decrease the effectiveness of this drug for hypothyroidism and raise levels of thyroid-stimulating hormone (TSH). Blood tests may be needed to see if the dosage needs to be adjusted.
  • Lanoxin (digoxin): Your body's use of Lanoxin, which is used to treat heart failure or abnormal heart rhythms, may also be affected by gastric pH. In this case, a higher gastric pH can make digoxin at least 10% more potent. Patients who take both medications may need to be monitored for digoxin toxicity.
  • Calcium supplements: Absorption of certain calcium supplements, such as calcium carbonate, may be impaired due to gastric pH. If you are taking calcium carbonate, it's best to take it with a meal. You might also consider switching to calcium citrate, which may not be affected by gastric pH.
  • Iron supplements (iron salts): The amount of the iron supplement that enters your bloodstream may be lowered due to gastric pH while taking omeprazole.
  • Trexall (methotrexate): Blood levels of this drug used to treat cancer, rheumatoid arthritis, and psoriasis may be elevated and prolonged if taken along with omeprazole. Blood tests may be needed to check the dosage.
  • Dilantin (phenytoin): Your body's elimination of this anti-seizure drug can also be prolonged when taken with Prilosec. Blood tests may be needed to see if the dosage needs to be adjusted.
  • Antiretroviral drugs: Taking omeprazole along with antiviral therapies to treat HIV can cause an interaction that increases or decreases the potency of the antiretrovirals. Prilosec along with Reyataz (atazanavir) or Viracept (nelfinavir) can substantially decrease blood levels of these HIV drugs, while taking Prilosec with Norvir (saquinavir) may increase the potency of Norvir.
  • Immunosuppressive drugs: Blood levels of Prograf (tacrolimus), used to reduce the risk that your body will reject an organ transplant, can increase when it is taken with omeprazole. Your body's elimination of Sandimmune (cyclosporine), another drug used for transplants, may be prolonged when taken with omeprazole. Tests may be needed to check dosages.
  • Antabuse (disulfiram): Your body's elimination of this drug used to treat chronic alcohol dependence may be prolonged when taken along with omeprazole. Tests may be needed to check the dosage.
  • Ampicillin: This antibiotic can also be affected by gastric pH and may become less potent.
  • Rifadin (rifampin): Rifadin, which is used to treat tuberculosis (TB), can speed up how fast your liver processes omeprazole, making omeprazole less potent and effective.
  • Pletal (cilostazol): Concentrations of this drug, which is used to improve blood flow in the legs and treat leg pain, are increased when it is taken with omeprazole. Dosages of cilostazol may need to be reduced from 100 mg twice daily to 50 mg twice daily.
  • St. John's Wort: This supplement may speed up how fast your liver processes omeprazole, making omeprazole less potent and effective.

If you are using a combination therapy to treat H. pylori, the other drugs in the regimen—such as the antibiotic Bioxin (clarithromycin)—can have other serious drug interactions.

Complications with Long-Term Use

Over-the-counter PPIs are meant to only be taken for a few weeks, and ideally under the supervision of a practitioner. If you need these medications long term, you should discuss this treatment with your healthcare provider.

Prilosec and other proton-pump inhibitors may interfere with certain tests and have been linked to certain medical risks when they are taken long-term, such as:

  • Bone fractures: Taking Prilosec long-term and multiple times a day may increase your risk of bone fractures, including fractures of the wrist, spine, and hip. The highest number of such fractures occurs in people who take these drugs at high doses for a year or longer.
  • Low magnesium: In rare cases, prolonged treatment of omeprazole can lead to low magnesium, which can turn serious and become life-threatening since magnesium is needed for multiple body processes and organ functions. Your healthcare provider may want to do periodic blood tests to monitor your magnesium levels if you plan to take Prilosec for more than three months.
  • Gastritis: Chronic inflammation of the stomach lining can happen with long-term use of omeprazole.
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10 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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