Based on NIH | Is fatigue a known side effect of omeprazole, how common is it, and when should I contact a doctor?

Fatigue can occur with omeprazole, but it appears to be uncommon and is not among the most frequently reported side effects. Official prescribing information lists “fatigue” among postmarketing adverse events reported with omeprazole, but because these are reported from an uncertain number of people, the exact rate is not known. ^{[1] [2]} Consumer medication guides emphasize common effects like headache, stomach pain, nausea, diarrhea, vomiting, and gas, and do not list fatigue among the most common reactions. ^{[3] [4]}

What official sources say

• The professional label includes “fatigue” in the “Body as a whole” section of adverse events reported after the drug was approved, noting these reports cannot be used to estimate frequency or prove causation. ^{[1] [2]}
• Patient-facing guides list the most common side effects (headache, abdominal pain, nausea, diarrhea, vomiting, gas), which suggests fatigue is less common than these listed effects. ^{[3] [4]}

How common is it?

There is no precise percentage for fatigue with omeprazole, because reports came from postmarketing experience without a known denominator, so the frequency cannot be reliably estimated. ^[2] Evidence summaries for common side effects focus on gastrointestinal symptoms and headache, implying that if fatigue occurs, it is relatively infrequent compared with those effects. ^{[3] [4]}

Possible related issues to consider

• Low magnesium (hypomagnesemia) has rarely occurred with prolonged PPI use and can cause symptoms such as tiredness, dizziness, irregular heartbeat, muscle weakness, tingling, or mood changes; these require medical attention. ^{[5] [6]}
• Overall, PPIs are considered safe, and serious adverse events are uncommon, but monitoring is reasonable if new, persistent fatigue appears after starting therapy. ^[7]

When to contact a doctor

• Seek prompt care if fatigue is accompanied by signs that could indicate a serious problem, such as irregular or fast heartbeat, dizziness/fainting, shortness of breath, severe muscle weakness, confusion, or tingling/numbness, which can be signs of low magnesium. ^{[5] [6]}
• Contact a doctor soon if fatigue is new, persistent, or bothersome after starting omeprazole, even without other symptoms, to review whether the medicine could be contributing and to rule out other causes. ^{[8] [9]}
• Get urgent help for any signs of an allergic reaction (rash, facial swelling, throat tightness, difficulty breathing) or for red‑flag heartburn symptoms such as chest pain with shortness of breath, lightheadedness, or black/bloody stools. ^{[8] [10]}

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Quick reference table

Topic	Key points
Is fatigue a known side effect?	Listed among postmarketing adverse events for omeprazole. [1] [2]
How common is it?	Exact frequency is unknown; not among the most commonly listed effects. [2] [3] [4]
Common side effects	Headache, stomach pain, nausea, diarrhea, vomiting, gas. [3] [4]
Serious signs linked to electrolytes	Possible low magnesium after prolonged use: tiredness with dizziness, irregular heartbeat, muscle weakness, tingling, or mood changes. [5] [6]
When to seek help	New or persistent fatigue; urgent care for allergic reactions or cardiac/GI alarm symptoms. [8] [10]

Practical steps if you feel fatigued on omeprazole

• Consider timing and dose review with your clinician if fatigue began after starting or increasing omeprazole, as an individualized adjustment or an alternative therapy may help. ^[8]
• If you have been on long-term therapy, your clinician may consider checking magnesium levels, particularly if you have accompanying symptoms like palpitations or muscle cramps. ^[3]
• Do not stop a prescribed PPI abruptly without medical guidance, especially if it was recommended for a specific diagnosis; stopping can lead to rebound acid symptoms. ^[7]

If you’d like, I can help you think through your symptoms’ timing, dose, and any other medications or conditions that might contribute to fatigue?