What Is the Most Common Side Effect of Lansoprazole?

October 8, 2025 •

4 min read

Clinical studies indicate that lansoprazole is generally well-tolerated, but common side effects do occur, with one of the most frequently reported being headache, often closely followed by diarrhea. Understanding what is the most common side effect of lansoprazole is key for patients to anticipate and manage potential issues effectively.

Quick Summary

Headache and diarrhea are among the most frequently reported adverse effects of lansoprazole, a proton pump inhibitor. Most side effects are mild and transient, but long-term use can pose other risks, including nutritional deficiencies and potential infections.

Key Points

Headache and Diarrhea are Primary Concerns: Clinical data consistently identifies headaches and diarrhea as the most common side effects of lansoprazole, though they are typically mild and self-limiting.
Other Common Effects Include GI Issues: Patients may also experience other gastrointestinal symptoms like nausea, abdominal pain, constipation, and gas.
Lifestyle Management Helps: Common side effects can often be managed through simple adjustments like staying hydrated, eating smaller meals, increasing fiber, and getting rest.
Long-Term Use Has Unique Risks: Prolonged use (over one year) is associated with an increased risk of bone fractures, low magnesium, vitamin B12 deficiency, and gut infections.
Serious Side Effects Require Immediate Attention: Severe symptoms like bloody diarrhea, signs of an allergic reaction, or kidney issues warrant contacting a doctor immediately.
PPIs Have Similar Side Effect Profiles: Lansoprazole's common side effects are broadly similar to other proton pump inhibitors like omeprazole and pantoprazole, though minor differences in frequency can occur.

The Most Common Side Effects: Headache and Diarrhea

When considering what is the most common side effect of lansoprazole, research points to headache as a leading contender, with diarrhea also being very common. In many clinical trials, these two side effects are reported with similar frequency, often appearing in more than 1 in 100 people. For most patients, these reactions are mild and tend to resolve on their own as the body adjusts to the medication. For instance, headaches associated with lansoprazole often subside after the first week of treatment.

For headaches, simple management strategies like staying hydrated, resting, and avoiding excess alcohol can be effective. For gastrointestinal issues like diarrhea, ensuring you drink plenty of fluids is crucial to prevent dehydration. If these symptoms persist or worsen, it is important to contact a healthcare provider.

Other Frequent Adverse Reactions

In addition to headache and diarrhea, other common side effects that can occur while taking lansoprazole include:

Nausea: Some individuals may experience an upset stomach or feeling sick, which can sometimes be alleviated by not eating rich or spicy food.
Abdominal Pain: Stomach pain is another common complaint. Eating smaller, more frequent meals and using a heat pad can sometimes provide relief.
Constipation: While diarrhea is more common, some patients experience constipation instead. This can be managed by increasing fiber intake, drinking plenty of water, and regular exercise.
Gas (Wind): Increased gas or flatulence can also occur. Avoiding foods known to cause gas, eating slowly, and exercising can be helpful.

Managing Common Lansoprazole Side Effects

Side effects are often manageable with simple lifestyle adjustments. If you experience these issues, consider the following strategies:

Dealing with Headache

Stay hydrated: Drink plenty of water throughout the day.
Rest: Ensure you are getting adequate rest, especially during the first week of starting the medication.
Use over-the-counter pain relief: Consult your pharmacist for a suitable painkiller if needed.

Alleviating Gastrointestinal Discomfort

Manage diarrhea: Drink small, frequent sips of water or squash to prevent dehydration. Avoid taking anti-diarrhea medication without consulting a doctor.
Address constipation: Increase your intake of dietary fiber, fresh fruits, vegetables, and cereals. Increase physical activity, such as a daily walk.
Reduce nausea: Try eating smaller, more frequent meals and avoid rich or spicy foods.

Long-Term and Serious Adverse Effects

While uncommon, long-term use of lansoprazole (typically over one year) can be associated with more significant risks. These include:

Vitamin B12 deficiency: Long-term acid suppression can interfere with the absorption of vitamin B12, potentially leading to symptoms like extreme tiredness, a sore tongue, or neurological issues.
Low magnesium levels (Hypomagnesemia): Patients on lansoprazole for extended periods may develop low magnesium levels, which can cause serious symptoms such as muscle spasms, irregular heartbeats, and seizures.
Increased risk of bone fractures: Long-term, high-dose use of PPIs has been linked to a higher risk of fractures in the hip, wrist, or spine, particularly in older adults.
Increased risk of gut infections: The reduction in stomach acid can allow for an overgrowth of bacteria, increasing the risk of Clostridioides difficile (C. diff) infection, which causes severe diarrhea.

Lansoprazole vs. Other Proton Pump Inhibitors (PPIs)

Although all PPIs share a similar mechanism and common side effects, minor differences in the incidence of certain reactions can exist. For instance, some studies have shown lansoprazole to be associated with slightly higher rates of diarrhea compared to omeprazole or pantoprazole, particularly in the elderly. The decision on which PPI to use is made by a healthcare provider, considering the patient's specific condition and risk factors.

Comparison of Common PPI Side Effects


Feature	Lansoprazole (Prevacid)	Omeprazole (Prilosec)	Pantoprazole (Protonix)
Most Common Side Effects	Headache and Diarrhea	Headache, diarrhea, nausea, abdominal pain	Headache, diarrhea, nausea, abdominal pain
GI Side Effects	Diarrhea potentially more frequent, especially in the elderly	Generally similar GI side effects to other PPIs	Similar GI side effects, but less data comparing frequency
Long-Term Risks	Same general long-term risks (fractures, B12, Mg)	Same general long-term risks (fractures, B12, Mg)	Same general long-term risks (fractures, B12, Mg)
Drug Interactions	Fewer CYP interactions reported than omeprazole, but potential exists	Noted interactions with some drugs (e.g., clopidogrel) via CYP2C19	Fewer CYP interactions reported

When to Contact a Doctor

While most side effects are mild, some symptoms warrant immediate medical attention. Call your doctor immediately if you experience:

Severe, watery, or bloody diarrhea
Signs of a kidney problem, such as a decrease in the amount you urinate, or swelling of the ankles, feet, or hands
Symptoms of a serious allergic reaction, such as a rash, hives, difficulty breathing, or swelling of the face, throat, or tongue
Severe chest pain or pain that spreads to the neck, jaw, or arms
Unexplained weight loss or difficulty swallowing

Conclusion

While lansoprazole is a highly effective medication for reducing stomach acid, it is associated with a range of side effects, with headache and diarrhea being the most common. For the majority of users, these effects are minor and temporary. However, it is essential for patients to be aware of the full spectrum of potential side effects, including the more serious, though rare, long-term risks associated with prolonged use. Regular consultation with a healthcare provider is the best way to ensure that the medication remains safe and appropriate for your needs. If you experience any concerning symptoms, seeking professional medical advice is crucial. You can also consult resources like the NHS for reliable information on managing common side effects.

Frequently Asked Questions

Diarrhea is a common side effect of lansoprazole and is usually mild and temporary. However, you should contact your doctor if you experience severe, watery, or bloody diarrhea, as it could be a sign of a more serious infection like Clostridioides difficile.

Yes, long-term use of lansoprazole (typically over one year) can be associated with increased risks, including bone fractures, low magnesium levels, and vitamin B12 deficiency.

Yes, higher doses of lansoprazole may increase the likelihood or severity of side effects. For instance, the risk of long-term side effects like bone fractures is higher with higher doses and prolonged use.

For some conditions like severe GERD, indefinite daily use may be recommended by a doctor. For many people, a short course is sufficient. Regular evaluation by a healthcare provider is recommended for those on long-term therapy to assess its continued necessity and safety.

To manage common gastrointestinal issues like nausea, abdominal pain, or constipation, you can try eating smaller meals, avoiding trigger foods, increasing your intake of water and fiber, and getting regular exercise.

Signs of a serious reaction include a skin rash, hives, swelling of the face or throat, difficulty breathing, bloody or severe diarrhea, irregular heartbeats, muscle spasms, or signs of kidney injury.

While all proton pump inhibitors (PPIs) have similar effects and general safety profiles, there can be minor differences. Some studies suggest lansoprazole may have a slightly higher incidence of diarrhea compared to omeprazole and pantoprazole, particularly in elderly patients.