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Omeprazole

Brand names: Prilosec, Prilosec OTC

Omeprazole is a proton pump inhibitor (PPI) that lowers stomach acid to treat heartburn, reflux, and ulcers.

Brand namesPrilosec, Prilosec OTC
Type of medicineProton pump inhibitor (acid reducer)
Prescription?Both prescription and over the counter
ImportantThis page is general information, not a prescription. Don't start, stop, or change a medicine without talking to your provider or pharmacist.

Overview

It turns down the pumps in the stomach lining that make acid. It takes 1 to 4 days to work fully, so it's not for instant heartburn relief.

What it's used for

  • Frequent heartburn and acid reflux (GERD)
  • Stomach and duodenal ulcers
  • Healing an irritated esophagus
  • Part of treatment for H. pylori infection

How to take it

  • Take it before a meal, usually 30 to 60 minutes before breakfast.
  • Swallow capsules whole. Some capsules can be opened and sprinkled on applesauce; check your label.
  • The over-the-counter version is a 14-day course. Don't repeat it more than every 4 months without seeing a provider.

Your dose depends on your health and other medicines. Always follow your prescription label, and ask your pharmacist if anything is unclear.

Side effects

Common side effects

  • Headache
  • Stomach pain, gas, nausea
  • Diarrhea or constipation
Call your provider todaySevere, watery diarrhea that won't stop (possible C. diff infection)
Call your provider todayMuscle cramps, shakiness, or a jumpy heartbeat (possible low magnesium)
Call your provider todayPeeing less, blood in urine, or a rash with joint pain

Warnings

  • Long-term use is linked to low magnesium and B12 and a higher risk of bone fractures.
  • See a provider if you have trouble swallowing, vomiting blood, black stools, or unplanned weight loss; these need checking.
  • Don't stop suddenly after long use without asking; heartburn can rebound.

Other medicines, foods, and alcohol

  • It can weaken clopidogrel (Plavix).
  • It can change levels of methotrexate, some HIV medicines, and tacrolimus.
  • It lowers absorption of some medicines that need stomach acid, like certain antifungals and iron.

Tell your provider and pharmacist about every medicine, vitamin, and supplement you take.

Pregnancy and breastfeeding

Talk with your provider. Omeprazole has been used in pregnancy when needed.

Missed doses, overdose, and storage

If you miss a dose

Take it as soon as you remember, unless it's almost time for your next dose. Then skip the missed dose. Don't take two doses at once.

If someone takes too much

Call Poison Control at 1-800-222-1222 or get help online at poison.org. Call 911 if the person collapses, has a seizure, has trouble breathing, or can't be woken.

Storing it

Store at room temperature, away from heat and moisture (not in the bathroom), and out of reach of children and pets.

Conditions it's used for

Sources

Last updated 2026-11-13.