Lansoprazole side effects: what to expect and when to worry

Most people who take lansoprazole experience few or no side effects. When they do occur, they are usually mild and settle quickly.

The BNF reports the following as common side effects, affecting up to 1 in 10 patients.

Common side effects include:

• Headaches: the most frequently reported side effect, usually mild and responding well to paracetamol
• Diarrhoea: typically mild and self-limiting, occurring more often at the 30 mg dose
• Nausea or stomach pain: may occur during the first few days of treatment
• Constipation: less common than diarrhoea but still reported by some patients
• Flatulence and bloating: related to changes in stomach acid production
• Dizziness: occasional and usually mild

Why do these side effects occur?

Lansoprazole works by blocking the proton pump in the stomach lining, reducing acid production by up to 90 per cent.

This dramatic change in the stomach environment can temporarily affect digestion and cause the gastrointestinal symptoms listed above. Your body typically adapts within a few days to a week.

If any of these symptoms are persistent or troublesome, speak to your pharmacist or GP. A dose reduction from 30 mg to 15 mg may help, depending on the condition being treated.

While lansoprazole is safe for short-term use, long-term treatment (beyond 8 weeks) carries some additional risks that both patients and prescribers should be aware of.

The MHRA has issued several safety communications about the long-term use of PPIs.

Bone fracture risk:

Studies have shown that long-term PPI use is associated with a modestly increased risk of hip, wrist, and spine fractures. This is thought to be related to reduced calcium absorption.

The risk is greatest in older adults and those taking high doses for more than a year.

Magnesium deficiency (hypomagnesaemia):

The MHRA advises that PPIs can cause low magnesium levels, particularly after three months or more of use. Symptoms include muscle cramps, tremor, irregular heartbeat, and fatigue.

Your doctor may check your magnesium levels periodically during long-term treatment.

Vitamin B12 deficiency:

Reduced stomach acid impairs the absorption of vitamin B12. Long-term PPI users may develop B12 deficiency, causing tiredness, pins and needles, and in severe cases, neurological symptoms.

Clostridium difficile infection:

Reduced stomach acid may increase susceptibility to gut infections, including C. difficile, particularly in hospitalised patients or those also taking antibiotics.

Kidney effects:

Rare reports of interstitial nephritis (kidney inflammation) have been associated with PPI use. This is generally reversible if the medication is stopped promptly.

NICE recommends regular review of PPI prescriptions to ensure ongoing use is justified. Many patients are prescribed PPIs indefinitely when shorter courses would suffice.

Some side effects of lansoprazole are uncommon or rare but important to recognise.

• Skin reactions: rashes, including rare cases of Stevens-Johnson syndrome and toxic epidermal necrolysis. Stop the medication and seek medical help if you develop a severe rash with blistering
• Liver effects: raised liver enzymes are occasionally seen on blood tests. Hepatitis is very rare but has been reported
• Blood disorders: very rarely, lansoprazole can affect blood cell counts, causing anaemia, low white cell counts, or reduced platelets
• Joint pain: some patients report aching joints, which usually resolves on stopping the medication
• Visual disturbances: blurred vision has been reported rarely
• Subacute cutaneous lupus erythematosus (SCLE): a rare skin condition that can develop weeks to years after starting a PPI. It presents as red, scaly patches on sun-exposed skin

The BNF notes that these rare side effects are class effects common to all PPIs, not unique to lansoprazole.

If you experience any unusual or persistent symptoms while taking lansoprazole, report them to your doctor or pharmacist.

You can also report suspected side effects directly to the MHRA through the Yellow Card scheme.

Lansoprazole can interact with other medicines in ways that may cause or worsen side effects. The BNF lists several important interactions.

Key interactions to be aware of:

• Clopidogrel: lansoprazole may reduce the effectiveness of clopidogrel by inhibiting the enzyme that activates it. If you take clopidogrel, your doctor may prefer omeprazole-free alternatives or consider pantoprazole instead
• Methotrexate: PPIs can increase methotrexate levels in the blood, raising the risk of toxicity. The MHRA advises caution with concurrent use, particularly at high methotrexate doses
• Warfarin: lansoprazole may slightly increase the anticoagulant effect of warfarin. More frequent INR monitoring may be needed
• HIV medications (atazanavir, rilpivirine): lansoprazole significantly reduces the absorption of these drugs. Concurrent use is generally not recommended
• Antifungals (itraconazole, ketoconazole): reduced stomach acid decreases the absorption of these medications

Supplements and over-the-counter medicines:

• Iron supplements: absorption may be reduced. Take iron at least two hours apart from lansoprazole
• Calcium supplements: choose calcium citrate rather than calcium carbonate, as it is better absorbed in a low-acid environment
• St John's wort: may reduce lansoprazole levels, making it less effective

Always inform your pharmacist and doctor about all medicines and supplements you are taking.

There are several practical steps you can take to reduce the likelihood and severity of lansoprazole side effects.

Short-term use:

• Take lansoprazole first thing in the morning, 30 minutes before breakfast, for optimal absorption
• If you experience headaches, ensure you are well hydrated and try paracetamol
• For diarrhoea, maintain fluid intake and eat bland foods until it settles
• If nausea occurs, taking the capsule with a small amount of food may help

Long-term use:

• Ask your GP to review your prescription regularly (NICE recommends at least annually)
• Request blood tests for magnesium, vitamin B12, and kidney function if you have been taking lansoprazole for more than a year
• Ensure adequate calcium and vitamin D intake to protect bone health
• Discuss whether a lower dose or intermittent use might be appropriate for your condition

Stepping down or stopping:

• Do not stop lansoprazole abruptly if you have been taking it for more than four weeks, as rebound acid hypersecretion can occur
• Your doctor may recommend a gradual dose reduction over two to four weeks
• For some conditions, switching to an as-needed approach (taking lansoprazole only when symptoms occur) is effective

If you are unsure whether you still need lansoprazole, book a medication review with your GP or pharmacist.