Lansoprazole and omeprazole are commonly prescribed proton pump inhibitors (PPIs) that reduce stomach acid production by blocking proton pumps in the stomach lining, so both are used for acid reflux, heartburn, gastro oesophageal reflux disease, and stomach ulcers. The effects lansoprazole has on tolerability are generally compared against omeprazole because their overall side effect profiles are broadly similar. Where they genuinely differ is narrower and more clinically specific than a general "which is gentler" ranking, most notably in how each interacts with clopidogrel, a difference that matters a great deal if you are taking it and is often left out of comparisons like this one.
This guide covers acid reflux symptoms and other common and serious side effects for both, what is actually established versus commonly repeated without a clear source, and the clopidogrel interaction specifically. Most side effects from both medicines are mild and transient, which helps explain why they are so widely used to reduce stomach acid in routine care.
Key things to know
- Both PPIs have broadly similar common side effects: headache, nausea, diarrhoea, constipation and stomach pain, with diarrhoea and constipation common to both.
- Omeprazole should generally be avoided in people taking clopidogrel. Lansoprazole is a preferred alternative.
- There is no established evidence that lansoprazole consistently causes more dizziness or fatigue than omeprazole.
- Long-term PPI treatment has several recognised safety considerations, including low magnesium levels and, in some circumstances, vitamin B12 deficiency and fracture risk. These concerns are generally considered at class level rather than showing that one of these two PPIs is consistently safer.
- Switching between lansoprazole and omeprazole may help manage side effects if one does not suit you, best done with your prescriber's guidance.
Common Side Effects: How They Compare
Omeprazole commonly causes headache, nausea, stomach pain, diarrhoea, constipation and wind, affecting up to around 1 in 10 people. Lansoprazole has a broadly similar common side-effect profile, with headache, nausea, diarrhoea, constipation and stomach-related symptoms among the reported effects.
You may see claims online that lansoprazole causes more dizziness and fatigue, or that omeprazole causes more gastrointestinal disturbance. These specific comparative claims are not well supported by established evidence, both medicines have similar overall tolerability. Individual response can vary, and there is no established basis for ranking one as consistently better tolerated overall.
The Genuine Difference: Clopidogrel Interaction
One of the clinically significant, well-established differences between lansoprazole and omeprazole concerns their interaction with clopidogrel.
UK specialist pharmacy guidance (NHS Specialist Pharmacy Service) advises avoiding omeprazole in people taking clopidogrel, because omeprazole inhibits CYP2C19, the enzyme involved in converting clopidogrel to its active metabolite, which can reduce clopidogrel activation. Esomeprazole carries the same caution.
Lansoprazole is one of the preferred PPIs for people taking clopidogrel, alongside pantoprazole and rabeprazole, since its effect on CYP2C19 is considered clinically insignificant.
If you are taking clopidogrel, typically after a heart attack, stroke, or stent, and need a PPI.
This interaction matters because clopidogrel is used to reduce the risk of blood clots.
This is a genuine, evidence-based reason to choose lansoprazole over omeprazole, not a matter of general preference. More broadly, drug interactions may occur with both medications, particularly omeprazole.
Serious but Rare Side Effects
Both medicines can rarely cause serious reactions, including severe allergic reactions. Seek urgent medical attention for facial or throat swelling, difficulty breathing or a severe widespread rash. Seek medical advice if you develop symptoms that could indicate a liver problem, such as yellowing of the skin or eyes or unusually dark urine.
Clostridioides difficile infection risk with prolonged use applies to PPIs as a class, not specifically more to one or the other.
Long-term PPI treatment can cause low magnesium levels, which may sometimes lead to muscle cramps, muscle twitches or an irregular heartbeat and, in severe cases, seizures. This is a recognised risk across the PPI class.
There is no established evidence that omeprazole has a higher kidney risk than lansoprazole specifically. If you develop symptoms such as reduced urination or swelling while taking either medicine, seek medical advice. Joint pain together with a rash on sun-exposed skin can rarely indicate subacute cutaneous lupus erythematosus, which has been reported with PPIs.
Long-Term Use Considerations
Long-term PPI treatment has been associated with low magnesium levels and, in some circumstances, vitamin B12 deficiency. Long-term PPI treatment has also been associated with an increased risk of fractures, particularly with prolonged or high-dose use. NICE recommends reviewing long-term PPI treatment and using the lowest dose needed to control symptoms where appropriate.
People taking PPIs long term should have their treatment reviewed periodically, with monitoring considered where clinically appropriate. Stopping PPIs suddenly may cause rebound acid secretion.
Other Medicines to Flag to Your Prescriber
Omeprazole has greater potential for CYP2C19-mediated drug interactions than lansoprazole, which is particularly relevant when you are taking medicines such as clopidogrel.
A healthcare professional should review other drugs and medical conditions before starting either medicine, and that matters for taking omeprazole or taking lansoprazole safely, not just prescription medicines.
Switching Between Lansoprazole and Omeprazole
If you are experiencing side effects with one, switching to the other is a reasonable option, but switching between lansoprazole and omeprazole should be discussed with your prescriber or pharmacist especially if one does not effectively treat acid reflux. This is worth discussing with your prescriber, particularly if you are taking clopidogrel or other medicines where the choice of PPI genuinely matters.
Available Treatments
Some omeprazole products are available without a prescription for short-term use, while prescription-only strengths and formulations are also available. Follow the specific product instructions.
| Treatment | Price |
|---|---|
| Lansoprazole 15mg Capsules | From £5.99 |
| Pantoprazole | From £5.99 |
| Famotidine Tablets | From £8.49 |
| Lansoprazole 15mg Orodispersible Tablets | From £8.49 |
| Esomeprazole | From £16.99 |
| Omeprazole 20mg | From £12.99 |
| Rabeprazole | From £19.99 |
| Losec MUPS 20mg Tablets | From £29.99 |
Medical Disclaimer
This guide provides general information comparing lansoprazole and omeprazole side effects. It is not a substitute for personalised medical advice. If you are taking clopidogrel or other medicines, tell your prescriber before starting either PPI, since this may affect which PPI is appropriate for you.
