Omeprazole: what it treats, how to take it, side effects
Last updated September 3, 2026.
Omeprazole is a proton pump inhibitor (PPI) that decreases the amount of acid your stomach makes. It comes in prescription strength and over the counter (Prilosec OTC and generics). It treats acid problems at the source rather than neutralizing acid that is already there, which is why it takes days to reach full effect.
What does it treat?
Over the counter, omeprazole treats frequent heartburn - heartburn that happens at least 2 days a week - in adults. By prescription it treats GERD and the esophagus damage GERD causes, stomach and duodenal ulcers, conditions where the stomach makes too much acid like Zollinger-Ellison syndrome, and, combined with antibiotics, H. pylori infections to keep ulcers from coming back.
How do you take it?
The over-the-counter course is strict: one tablet once a day in the morning before eating, every day for 14 days, and do not repeat a course more often than once every 4 months without a doctor. It is not for immediate relief - full effect takes 1 to 4 days. Prescription dosing on the label varies by condition: 20 mg once daily for up to 4 weeks for GERD symptoms, 20 mg once daily for 4 to 8 weeks for erosive esophagitis, 20 mg once daily for 4 weeks for duodenal ulcer, and 20 mg twice daily for 10 days as part of H. pylori triple therapy. Swallow delayed-release tablets and capsules whole; if you cannot swallow a capsule, you can open it, sprinkle the granules on a tablespoon of cool applesauce, and swallow immediately without chewing. If you miss a dose, take it when you remember unless the next one is close; never double up.
Side effects to know
- Common: headache, nausea, diarrhea, gas, constipation, and vomiting.
- Serious: severe skin reactions (blisters, peeling, sores on the lips or mouth); allergic reactions with facial or throat swelling; signs of low magnesium (irregular or pounding heartbeat, muscle spasms, tremors, seizures); severe watery diarrhea with stomach pain or fever; kidney problems (changes in urination, blood in urine, fever, rash); and new or worsening joint pain with a sun-sensitive rash. Long-term or high-dose use raises the risk of wrist, hip, and spine fractures and stomach lining polyps - talk to your doctor about how long you should stay on it.
Who should not take it?
Skip the over-the-counter version and see a doctor first if your heartburn comes with chest, shoulder, or arm pain, shortness of breath, sweating, unexplained weight loss, vomiting (especially bloody vomit), trouble swallowing, or black or bloody stools - those can signal something a PPI should not mask. Tell your clinician if you have osteoporosis, low magnesium, calcium, potassium, or B12 levels, lupus, or liver disease, and about everything you take - MedlinePlus flags interactions with iron supplements and St. John's wort, and the label notes lower doses for liver impairment. On pregnancy, the label says there are no adequate controlled studies but available data have not shown an increased risk of major birth defects with first-trimester use; ask a health professional before using it while pregnant or breastfeeding.
When is it an emergency?
Call 911 for an allergic reaction with swelling of the face, lips, tongue, or throat, or trouble breathing, and for a seizure. Chest pain with shortness of breath, sweating, or pain spreading to the arm, neck, or shoulder is a possible heart problem, not heartburn - treat it as an emergency. Severe, watery, or bloody diarrhea that will not stop needs same-day medical care. For an overdose, call Poison Control at 1-800-222-1222. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper.
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Common questions
How long does omeprazole take to work?
Not right away - and that is normal. MedlinePlus says it can take 1 to 4 days to feel the full benefit, so it should never be used for immediate relief of a heartburn flare. If symptoms are not better after 14 days, call your doctor.
Why is the over-the-counter course limited to 14 days?
The OTC label is designed for a single 14-day course, repeated no more often than once every 4 months, without a doctor's input. Heartburn that keeps coming back faster than that needs a diagnosis, not another course - you could be masking something more serious.
Why do I take omeprazole before eating?
Omeprazole shuts down the acid pumps your stomach switches on for meals, so it works best when it is already in your system. MedlinePlus directs taking it once a day before a meal, and the OTC label specifies the morning, at least an hour before eating.
Can I open the capsule instead of swallowing it?
Yes, carefully. MedlinePlus describes the method: empty the granules onto a tablespoon of cool, soft applesauce, swallow immediately with cool water, and never chew or crush the granules. Do not save the mixture for later.
Is it safe to take omeprazole for months or years?
That is a decision for your doctor, because the risks shift with time. MedlinePlus notes that people who take PPIs at high doses or for a year or longer are more likely to fracture their wrist, hip, or spine, and may develop fundic gland polyps on the stomach lining. Long-term users should be monitored, not self-managed.
Can I drink alcohol while taking omeprazole?
Neither the FDA label nor MedlinePlus lists a specific alcohol interaction for omeprazole. Alcohol can itself trigger heartburn, which works against the treatment, so ask your doctor what makes sense for you.