Based on NIH | Can omeprazole cause diarrhea, and when should I contact a doctor if it doesn’t improve?

Omeprazole can cause diarrhea in some people, and there are specific warning signs that mean you should contact a doctor promptly. ^[1] In most cases the diarrhea is mild and short‑lived, but omeprazole and other proton pump inhibitors can occasionally be linked to more serious diarrhea due to a gut infection called Clostridioides difficile. ^{[1] [2]}

How omeprazole can cause diarrhea

• Omeprazole reduces stomach acid, which can disrupt the normal balance of bacteria and allow certain germs to grow, leading to diarrhea. ^[2]
• Official patient information for omeprazole lists diarrhea as a potential side effect and notes the risk of severe diarrhea from C. difficile infection. ^{[1] [3]}
• In clinical studies and reviews, diarrhea appears among the most commonly reported (usually mild) side effects of omeprazole. ^{[4] [5]}

How common is it?

• Large clinical trial summaries have found that diarrhea occurs but is generally infrequent and typically mild, not requiring dose changes for most people. ^{[4] [5]}
• Observational data in long‑term PPI users suggest only a small percentage (around a few percent over a month) report diarrhea, with similar rates across different PPIs, including omeprazole. ^[6]

When to contact a doctor

• You should contact a doctor right away if you develop watery stools, stomach pain, and a fever that do not go away, since these can be signs of C. difficile infection. ^{[1] [2]}
• Seek care urgently if you notice signs of dehydration (such as dizziness, very dry mouth, or very little urine), blood in stool, or severe, persistent abdominal pain. ^[1]
• If diarrhea lasts more than a few days or keeps returning while you are taking omeprazole, it’s reasonable to contact your doctor for guidance. ^{[1] [2]}

What to do if diarrhea occurs

• Consider holding off on non‑essential diarrhea‑worsening foods (high‑fat, very spicy, high‑sugar substitutes like sorbitol) and keep hydrated with water or oral rehydration solutions.
• Do not take anti‑diarrheal medicines like loperamide if you have fever, blood in the stool, or severe pain; you should be evaluated first. ^[1]
• Your clinician may check for C. difficile if symptoms suggest it, and may decide whether to continue, pause, or switch acid‑reducing therapy. ^{[1] [2]}

Other warning signs to watch

• In rare cases, people on omeprazole can develop kidney problems such as acute interstitial nephritis; call a doctor right away if you notice a decrease in how much you urinate or blood in your urine. ^[3]
• Bone health issues and other long‑term risks have been noted with prolonged high‑dose PPI use, but these are not immediate causes of diarrhea; still, it’s good to review ongoing need for therapy with your doctor. ^[2]

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Quick reference: When to call a doctor

Situation	What it may mean	What to do
Watery diarrhea + stomach pain + fever that doesn’t go away	Possible C. difficile infection	Contact a doctor right away. [1] [2]
Diarrhea lasting more than a few days or recurring on omeprazole	Side effect or infection	Call your doctor for advice/testing. [1] [2]
Signs of dehydration (dizziness, very little urine), blood in stool, or severe abdominal pain	Complication or severe illness	Seek medical care promptly. [1]
Decreased urination or blood in urine	Possible kidney issue (interstitial nephritis)	Call your doctor right away. [3]

Bottom line

• Diarrhea can happen with omeprazole; it is often mild, but sometimes it can signal a more serious infection that needs treatment. ^{[1] [2]}
• Get medical help promptly if diarrhea is watery and persistent with fever and pain, if it lasts more than a few days, or if you notice any warning signs described above. ^{[1] [2]}