Omeprazole Side Effects: What to Know

Overview

Omeprazole is generally well-tolerated when used for appropriate durations and indications. Most people experience few or no side effects during short-term use, and when side effects do occur, they are typically mild. However, because omeprazole profoundly reduces stomach acid, there are some important considerations for long-term use. Understanding the potential side effects, their frequency, and when they warrant medical attention can help people use omeprazole safely and know when to seek guidance from a healthcare provider.

This page provides detailed information about omeprazole’s side effects, organized by frequency and severity, along with information about risk factors and when to seek medical care.

Common Side Effects

Side effects from omeprazole during short-term use are generally uncommon and mild when they occur.

Headache

Headache is one of the most commonly reported side effects of omeprazole, occurring in approximately 2 to 7% of people taking the medication. The headaches are generally mild and often resolve on their own without requiring discontinuation of the medication.

The relationship between omeprazole and headache is not always clear, as headaches can occur for many reasons. Some people find that headaches decrease with continued use of the medication.

Nausea and Stomach Pain

Some people experience nausea or stomach discomfort while taking omeprazole, occurring in approximately 1 to 4% of users. This can be difficult to distinguish from the underlying condition being treated.

The discomfort is typically mild and may improve with continued use or when taking the medication before meals as directed.

Diarrhea

Diarrhea occurs in approximately 3 to 4% of people taking omeprazole. It is generally mild and resolves on its own.

Managing mild diarrhea:

Stay well-hydrated
Eat bland, easily digestible foods
Monitor for signs of dehydration
Avoid foods that worsen diarrhea

Severe or persistent diarrhea, especially if accompanied by fever or abdominal pain, may indicate C. difficile infection and requires medical attention.

Gas (Flatulence)

Flatulence or increased gas is reported by some people taking omeprazole, occurring in approximately 1 to 3% of users. This is generally mild and often resolves with continued use.

Vomiting

Vomiting occurs in approximately 1 to 3% of people taking omeprazole. If vomiting is severe or persistent, medical evaluation is appropriate.

Less Common Side Effects

Some side effects occur less frequently but are still reported by people taking omeprazole.

Dizziness

Dizziness may occur in some people taking omeprazole, though it is uncommon. When it occurs, it is typically mild.

Constipation

Some people experience constipation while taking omeprazole. This is generally mild and can often be managed with dietary changes and increased fluid intake.

Rash or Skin Reactions

Mild skin reactions such as rash or itching may occur. While usually mild, skin reactions should be monitored, as they can occasionally indicate an allergic reaction or more serious skin condition.

Back Pain

Back pain has been reported in some people taking omeprazole, though a direct causal relationship is not always clear.

Cough

Some people report cough while taking omeprazole. This may be related to the underlying condition (such as acid reflux causing throat irritation) or the medication itself.

Other Less Common Effects

Additional less common side effects may include:

Dizziness
Drowsiness or fatigue
Muscle pain
Weakness
Fever
Changes in taste
Dry mouth

Side Effects Associated with Long-Term Use

While omeprazole is generally safe for short-term use, long-term use (several months to years) has been associated with certain concerns. These effects are generally related to the profound reduction in stomach acid over extended periods.

Vitamin B12 Deficiency

Stomach acid is needed to release vitamin B12 from food so it can be absorbed. Long-term use of omeprazole can reduce vitamin B12 absorption, potentially leading to deficiency.

Signs of vitamin B12 deficiency may include:

Fatigue or weakness
Pale skin
Shortness of breath
Dizziness
Numbness or tingling in hands and feet
Difficulty walking or balance problems
Memory problems or confusion
Mood changes

People using omeprazole long-term (especially those at higher risk, such as elderly individuals or vegetarians) should discuss vitamin B12 monitoring with their healthcare provider.

Magnesium Deficiency

Prolonged use of omeprazole (typically one year or longer) can lead to low magnesium levels in some people. This is more common with higher doses and longer durations of use.

Signs of low magnesium may include:

Muscle spasms or tremors
Irregular heartbeat
Seizures
Fatigue
Weakness

Serious cases of low magnesium can cause abnormal heart rhythms. People using omeprazole long-term should discuss magnesium monitoring with their healthcare provider, particularly if taking diuretics or digoxin.

Bone Fractures

Long-term use of omeprazole, particularly at high doses, has been associated with an increased risk of bone fractures, especially of the hip, wrist, and spine. The risk appears to be higher in elderly individuals and those using high doses for extended periods.

The mechanism is not fully understood but may relate to reduced calcium absorption or effects on bone metabolism when stomach acid is chronically suppressed.

Risk reduction strategies:

Use the lowest effective dose
Use for the shortest duration necessary
Ensure adequate calcium and vitamin D intake
Engage in weight-bearing exercise
Discuss bone health monitoring with a healthcare provider for long-term use

Increased Risk of Infections

Reducing stomach acid can affect the body’s natural defense against certain infections.

Infections that may be more common with long-term PPI use:

Pneumonia (particularly community-acquired pneumonia)
Clostridium difficile (C. diff) intestinal infection
Other gastrointestinal infections

Stomach acid normally helps kill bacteria and other organisms that enter the digestive system. Reducing acid may allow these organisms to survive and cause infection.

People should be aware of symptoms of infection and seek medical care if they develop severe diarrhea, fever, persistent cough, or difficulty breathing.

Kidney Problems

Long-term use of PPIs, including omeprazole, has been associated with an increased risk of kidney problems in some studies, including:

Acute kidney injury
Chronic kidney disease
Acute interstitial nephritis (kidney inflammation)

The risk appears to be relatively low, but people using omeprazole long-term should discuss kidney function monitoring with their healthcare provider, particularly if they have existing kidney disease or other risk factors.

Signs of kidney problems may include:

Decreased urination or changes in urine output
Swelling of feet, ankles, or legs
Unusual fatigue
Nausea or loss of appetite

Vitamin and Mineral Absorption

Besides vitamin B12 and magnesium, long-term acid suppression may affect the absorption of other nutrients, including:

Iron (stomach acid helps release iron from food)
Calcium (absorption may be reduced)
Vitamin C

Regular monitoring and supplementation may be appropriate for long-term users.

Rare but Serious Side Effects

Serious side effects from omeprazole are rare, but they require prompt medical attention when they occur.

Severe Allergic Reactions

Although uncommon, some people can have an allergic reaction to omeprazole itself.

Signs of a severe allergic reaction may include:

Difficulty breathing or wheezing
Swelling of the face, lips, tongue, or throat
Severe rash, hives, or itching
Tightness in the chest
Rapid heartbeat
Severe dizziness or fainting

These symptoms require emergency medical attention. Anaphylaxis (a severe, life-threatening allergic reaction) is extremely rare but possible.

Severe Skin Reactions

Very rare but serious skin reactions have been reported with omeprazole, including:

Stevens-Johnson syndrome
Toxic epidermal necrolysis
Acute generalized exanthematous pustulosis (AGEP)

Warning signs may include:

Severe rash with blistering and peeling skin
Rash accompanied by fever
Mouth sores or painful skin lesions
Rash spreading rapidly over the body

These conditions are medical emergencies requiring immediate care.

Lupus-Like Syndrome

Rare cases of cutaneous lupus erythematosus (lupus affecting the skin) and systemic lupus erythematosus have been reported with PPI use, including omeprazole.

Signs may include:

New or worsening joint pain
Rash on sun-exposed areas
Fatigue
Fever

People with existing lupus should inform their healthcare provider before using omeprazole.

Clostridium Difficile Infection

Omeprazole use can increase the risk of C. difficile infection, a serious intestinal infection that causes severe diarrhea.

Signs of C. difficile infection:

Severe, persistent diarrhea (often watery)
Frequent bowel movements
Abdominal pain or cramping
Fever
Blood or pus in stool

This condition requires immediate medical attention and treatment with specific antibiotics.

Liver Problems

Rare cases of liver injury have been reported with omeprazole use.

Signs of liver problems may include:

Jaundice (yellowing of the skin or whites of the eyes)
Dark urine
Pale or clay-colored stools
Severe fatigue
Loss of appetite
Abdominal pain, particularly in the upper right side
Nausea or vomiting

These symptoms require medical evaluation.

Interaction with Clopidogrel (Plavix)

While not a direct side effect, omeprazole can reduce the effectiveness of clopidogrel (Plavix), a medication used to prevent blood clots. This interaction can increase the risk of heart attack or stroke in people taking clopidogrel.

People taking clopidogrel should inform their healthcare provider before using omeprazole, as alternative acid-reducing medications may be more appropriate.

Risk Factors for Side Effects

Certain factors may increase the likelihood or severity of side effects from omeprazole.

Elderly individuals:

May be more prone to bone fractures with long-term use
Higher risk of vitamin B12 deficiency
May be more susceptible to infections
Should use the lowest effective dose for the shortest necessary duration

Duration and Dose

Higher doses and longer duration of use increase the risk of side effects, particularly those related to vitamin and mineral deficiencies, bone fractures, and infections
Short-term use (14 days for over-the-counter) has a lower risk profile than long-term use

Concurrent Medications

Taking omeprazole along with certain other medications can increase risks:

Clopidogrel (Plavix): Reduced effectiveness
Diuretics: May increase risk of low magnesium
Digoxin: Increased digoxin levels may occur
Methotrexate: Increased methotrexate levels may occur

Pre-Existing Conditions

People with certain conditions may be at higher risk:

Osteoporosis or low bone density: Higher risk of fractures with long-term use
Kidney disease: May be at higher risk for kidney-related side effects
Liver disease: May metabolize omeprazole differently
Lupus: Risk of worsening or triggering lupus symptoms

Individual Sensitivity

Some people are simply more sensitive to the effects of medications, including omeprazole. This individual variation is normal and unpredictable.

Comparing Side Effects with Other Acid-Reducing Medications

Omeprazole has a side effect profile similar to other proton pump inhibitors but different from other classes of acid-reducing medications.

Compared to H2 blockers (such as famotidine):

Omeprazole may have more concerns with long-term use due to more complete acid suppression
H2 blockers are associated with fewer concerns about bone fractures, vitamin B12 deficiency, and infections with long-term use
For short-term use, both are generally well-tolerated
H2 blockers may be preferable for people requiring long-term acid suppression if they provide adequate symptom control

Compared to antacids:

Different side effect profiles
Antacids can cause constipation (calcium-based) or diarrhea (magnesium-based)
Antacids do not have the long-term concerns associated with omeprazole
Antacids are appropriate for occasional use only

For detailed comparisons, see our famotidine vs omeprazole comparison page.

Managing Minor Side Effects

For people who experience mild side effects but need to continue using omeprazole, several strategies may help:

For headache:

Ensure adequate hydration
Take the medication at the same time each day
Monitor whether headaches decrease with continued use
Consider over-the-counter pain relief if appropriate

For nausea or stomach discomfort:

Take the medication before breakfast as directed
Ensure the delayed-release capsule is swallowed whole (not crushed or chewed)
Stay hydrated

For diarrhea:

Stay well-hydrated
Eat bland, easily digestible foods
Avoid foods that worsen symptoms
Contact a healthcare provider if diarrhea is severe or persistent

If side effects persist or worsen, consulting a healthcare provider is advisable.

Phenylketonuria Considerations

Some omeprazole formulations, particularly orally disintegrating tablets, contain phenylalanine, an amino acid that must be restricted in people with phenylketonuria (PKU).

People with PKU should carefully read product labels and choose formulations that do not contain phenylalanine, or consult with their healthcare provider about appropriate options. Standard delayed-release capsules do not typically contain phenylalanine.

When to Contact a Healthcare Provider

Medical guidance should be sought in certain situations related to side effects.

Contact a healthcare provider if:

Side effects persist or worsen over time
New or unusual symptoms develop after starting omeprazole
There is uncertainty about whether a symptom is related to the medication or the underlying condition
Side effects significantly interfere with daily activities
Symptoms do not improve despite using the medication as directed
Considering long-term use (more than a few months)
Using omeprazole and also taking clopidogrel (Plavix)
Questions arise about vitamin or mineral monitoring for long-term use

When to Seek Emergency Care

Some symptoms require immediate medical attention.

Seek emergency medical care if:

Difficulty breathing, wheezing, or chest tightness occurs
Severe swelling of the face, lips, tongue, or throat develops
Signs of anaphylaxis appear (severe rash, rapid pulse, dizziness, severe difficulty breathing)
Severe skin reaction develops (blistering, peeling, rash with fever)
Chest pain occurs, especially if accompanied by shortness of breath or pain radiating to arms or jaw
Vomiting blood or material that looks like coffee grounds
Black, tarry, or bloody stools appear
Severe diarrhea with fever occurs (may indicate C. difficile infection)
Jaundice (yellowing of skin or eyes) develops
Severe abdominal pain occurs
Signs of severe allergic reaction develop

These symptoms may indicate serious adverse reactions or other medical emergencies requiring immediate evaluation.

Important Safety Reminders

Short-Term Over-the-Counter Use is Safest

Over-the-counter omeprazole is intended for 14 days of use. This duration minimizes the risk of side effects associated with long-term use.

Long-Term Use Requires Medical Supervision

People who require omeprazole for extended periods should be under healthcare provider supervision to monitor for potential long-term effects and to ensure continued use is necessary.

Use the Lowest Effective Dose

Using the lowest dose that controls symptoms reduces the risk of side effects, particularly those associated with long-term use.

Report All Medications to Healthcare Providers

Always inform healthcare providers about all medications being taken, including over-the-counter omeprazole, to avoid potentially dangerous interactions (particularly with clopidogrel).

Do Not Ignore Warning Signs

New or unusual symptoms should not be ignored. Persistent or concerning symptoms warrant medical evaluation.

Sources

This information is based on data from the following authoritative sources:

U.S. Food and Drug Administration (FDA). Omeprazole Label Information.
MedlinePlus, U.S. National Library of Medicine. Omeprazole.
National Institutes of Health (NIH). Omeprazole—Adverse Effects Profile.
American Gastroenterological Association. Safety of Proton Pump Inhibitors.
FDA Adverse Event Reporting System (FAERS). Omeprazole Safety Data.
FDA Drug Safety Communication. Low Magnesium Levels with Long-Term PPI Use.
Clinical Gastroenterology and Hepatology. Long-Term Safety of Proton Pump Inhibitors.
Journal of the American Medical Association. PPI Use and Risk of Bone Fractures.