Omeprazole Non Generic Side Effects: What to Expect from Brand and Generic Versions

If you have just started omeprazole, or are about to, it is useful to know which side effects are common, which are less common but more serious, and whether it makes a difference if you are taking a branded product or a generic capsule. This guide looks at UK product information and explains what you can realistically expect rather than simply saying that "some people experience side effects".

Key things to know

• The most commonly reported omeprazole side effects are headache, abdominal pain, constipation, diarrhoea, wind, and nausea or vomiting
• These are listed as common side effects, affecting between 1 and 10 in every 100 people
• Branded omeprazole products such as Losec and Losec MUPS, and generic omeprazole, contain the same active ingredient, although their inactive ingredients and formulations can differ
• Omeprazole is not an antihistamine. It is a proton pump inhibitor, which is a completely different class of medicine

Is Omeprazole Generic or a Brand?

Both exist. Omeprazole is the generic, non-proprietary name for the active ingredient, and it is also sold under brand names such as Losec, Losec MUPS and Mepradec in the UK. In other markets, Prilosec is another brand name for omeprazole.

When people search for "omeprazole non generic", they are usually asking about these branded versions. They contain omeprazole as the active ingredient, but they can differ in their formulation and inactive ingredients, known as excipients.

Losec MUPS is a gastro-resistant tablet containing omeprazole in small gastro-resistant pellets. This gives it a different formulation from a standard gastro-resistant capsule, although both are designed to deliver omeprazole after it passes through the stomach.

For UK adults using or considering omeprazole, the practical questions are usually whether branded and generic versions work in the same way, how capsules and tablets differ, what side effects to expect, and when symptoms need medical advice.

Generic medicines have to meet regulatory requirements before they can be marketed in the UK. Where a generic is authorised as therapeutically equivalent to a reference product, it is expected to provide the same active medicine at the same strength, although its appearance and inactive ingredients may differ.

Can Different Brands of Omeprazole Work Differently?

The active ingredient is the same, but the products are not necessarily identical in every respect. Licensed generic products are assessed to show that they provide the expected exposure to the active ingredient compared with the relevant reference medicine.

The main differences are usually in the inactive ingredients and formulation. For example, Losec capsules contain lactose, while Losec MUPS tablets contain sucrose. Different generic manufacturers may use different excipients. This can matter if you have a particular intolerance or sensitivity.

Some people also feel that they tolerate one manufacturer's product better than another. That does not mean one brand is generally better for everyone. If you notice a consistent problem after changing manufacturers, speak to a pharmacist or prescriber.

Omeprazole Capsule vs Tablet

Many generic omeprazole products are supplied as gastro-resistant capsules. The coating helps protect the medicine from stomach acid so that the active ingredient can be released after it passes through the stomach.

Losec MUPS is a gastro-resistant tablet containing many small gastro-resistant pellets. Depending on the product instructions, the tablet can be swallowed whole or dispersed in water, which can be useful for people who have difficulty swallowing.

Both formulations are designed to protect omeprazole from stomach acid. The main difference is the formulation and how the medicine is taken, rather than a simple difference in the active ingredient.

What Are the Side Effects of Omeprazole?

According to UK product information, the most common side effects, affecting between 1 and 10 in every 100 people, are:

• Headache
• Abdominal pain
• Constipation
• Diarrhoea
• Flatulence (wind)
• Nausea and vomiting
• Benign fundic gland polyps (small, non-cancerous growths in the stomach lining)

There is not one single "biggest" side effect. Headache and the gastrointestinal effects above are all listed within the same common frequency category. Whether you experience any of them, and which one you notice, varies from person to person.

Does Omeprazole Cause Diarrhoea?

Yes. Diarrhoea is a common side effect of omeprazole. For many people it is mild, but it should not automatically be assumed to be caused by the medicine if it is severe, persistent or accompanied by other symptoms.

If you develop severe or ongoing diarrhoea, particularly if you have a fever or blood in your stools, speak to a GP or pharmacist promptly. Staying well hydrated is also important if you have diarrhoea.

PPIs such as omeprazole can slightly increase the risk of certain gastrointestinal infections, so persistent diarrhoea may need assessment rather than simply being treated as a normal adjustment to the medicine.

Omeprazole and Headaches

Headache is a common side effect of omeprazole. For many people, it is mild and does not last long.

If your headache is severe, keeps coming back, does not settle, or feels unusual for you, speak to a pharmacist or GP. They can help you work out whether omeprazole could be contributing to it or whether another cause should be considered.

Can Omeprazole Cause Stomach Ache or Nausea?

Yes. Abdominal pain and nausea, with or without vomiting, are both listed as common side effects.

This can seem strange because omeprazole is used to reduce stomach acid and treat conditions such as acid reflux. However, stomach discomfort or nausea can still occur while taking the medicine.

Mild symptoms may settle, but if abdominal pain is persistent, severe or getting worse, particularly if you develop other new symptoms, speak to your prescriber or pharmacist.

Why Side Effects Happen at All

Omeprazole is a proton pump inhibitor. It reduces the amount of acid produced by the stomach. This is why it is used for conditions such as acid reflux, gastro-oesophageal reflux disease (GORD), stomach ulcers and other acid-related conditions.

Stomach acid is part of the digestive process, and changing the amount of acid in the stomach can affect the gastrointestinal system. This may help explain why symptoms such as abdominal discomfort, diarrhoea, constipation, wind and nausea appear among the commonly reported side effects.

That does not mean these symptoms are a sign that the medicine is damaging your stomach. It simply means that side effects can occur alongside the intended effect of reducing stomach acid.

How Long Do Side Effects Usually Last?

There is no fixed amount of time that side effects will last. Some people may notice mild symptoms soon after starting omeprazole, while others may not experience any side effects at all.

If a side effect is mild but continues to bother you, or if it is getting worse rather than improving, speak to a pharmacist or GP. They can check whether the medicine is likely to be responsible and whether you need a different treatment or further assessment.

You should not stop a prescribed medicine simply because you have a mild side effect without checking with a healthcare professional first.

Less Common and Rare Side Effects

Beyond the common effects above, UK product information lists less common and rare reactions.

Uncommon side effects include raised liver enzymes, dermatitis, itching, rash, hives, fractures of the hip, wrist or spine, general malaise and swelling of the extremities.

Rare or very rare reactions include severe skin reactions, allergic reactions, liver problems, and certain blood or kidney problems. Low magnesium levels are listed with an unknown frequency and can be more relevant with longer-term treatment. Severe low magnesium can be associated with symptoms such as muscle twitches, weakness, dizziness or an irregular heartbeat.

These reactions are much less common than headache, stomach pain, diarrhoea or nausea. However, knowing about them can help you recognise when a symptom needs medical advice rather than assuming it is a normal side effect.

Is Omeprazole an Antihistamine?

No. Omeprazole is a proton pump inhibitor (PPI), not an antihistamine.

PPIs reduce the production of stomach acid. Antihistamines work on histamine receptors and are mainly used for allergies, although some types are also used for other conditions.

If you have seen omeprazole listed alongside antihistamines, it does not mean that omeprazole has antihistamine activity. They are different types of medicine.

Long-Term Side Effects to Be Aware Of

Long-term treatment with omeprazole can be appropriate for some people, but it is usually reviewed from time to time to make sure it is still needed and that the dose remains appropriate.

Longer-term PPI treatment has been associated with possible effects such as low magnesium levels, reduced vitamin B12 absorption, certain gastrointestinal infections and an increased risk of fractures in some people. Kidney problems have also been reported, although these are uncommon.

Some people also experience a return or increase in acid-related symptoms after stopping a PPI, particularly after longer periods of treatment. This can make it feel as though the medicine has caused dependence, but it is better described as a possible rebound increase in acid-related symptoms after stopping.

For people who need ongoing PPI treatment, guidance generally recommends reviewing the treatment periodically and using the lowest dose that controls symptoms when appropriate. The right approach depends on why the medicine was prescribed and the person's individual circumstances.

Prices shown are EverydayMeds' standard listed prices at the time of writing and can change, so it is worth checking the current figure at checkout before you order.

When to Seek Medical Advice

Speak to a GP or pharmacist if you have side effects that are severe, persistent or worrying.

You should seek prompt medical assessment for symptoms such as unexplained weight loss, difficulty swallowing, vomiting blood, black or tarry stools, or persistent severe stomach pain. These symptoms can have several possible causes and should not simply be assumed to be a side effect of omeprazole.

If you are taking omeprazole for heartburn or indigestion without a prescription, follow the instructions on the specific product you are using. Some pharmacy products are intended for short-term use, and self-treatment should not continue beyond the recommended period without medical advice. For example, UK pharmacy guidance limits some 20mg omeprazole products to use for up to 14 days without further assessment.

Persistent or changing symptoms also need assessment because acid-suppressing medicines can reduce some symptoms that may otherwise need investigation.

Medical Disclaimer

This article is provided for general information only and does not constitute medical advice. It is not a substitute for a consultation with a qualified healthcare professional. Treatment suitability depends on an individual clinical assessment, and your prescriber will determine the appropriate treatment for your circumstances. If you have questions about your own health, medication or symptoms, please speak to a pharmacist, your GP, or another appropriately qualified healthcare provider. In an emergency, call 999 or go to your nearest A&E.