Omeprazole

What is Omeprazole Used For?

Omeprazole treats several stomach and oesophageal conditions caused by excessive stomach acid. It is one of the most widely prescribed medications in the UK, with over 35 million prescription items dispensed in England alone in 2022–23. The treatment has been in clinical use for many years and has an established safety and efficacy record, making it a trusted first-line treatment for acid-related conditions in both primary and secondary care. 

Omeprazole is typically prescribed for the treatment of frequent heartburn and gastro-oesophageal reflux disease (GORD). It is available under several brand names, including Losec. 

What Does Omeprazole Do?

Omeprazole is a proton pump inhibitor (PPI), a class of medication that reduces stomach acid production. Some people produce too much acid, or it escapes into the oesophagus, which causes symptoms like heartburn, indigestion, and reflux. Omeprazole targets the root cause of acid overproduction by inhibiting H⁺/K⁺ ATPase, the acid pump in stomach lining cells and the final step in gastric acid production. This blocks acid production rather than simply neutralising it after the fact, making it more effective than antacid medications for sustained acid suppression. 

Unlike antacids, which neutralise acid on contact, omeprazole inhibits acid production at the source. It is absorbed after passing through the stomach and is activated in the acid-producing cells of the stomach lining. Blood levels peak around 1-2 hours after a dose, but the maximum acid-suppressing effect is usually achieved after about 4 days of daily use. By reducing acid levels, omeprazole allows damaged tissue in the oesophagus and stomach to heal while preventing further injury.

How Long Does Omeprazole Take to Work?

Omeprazole can reduce both daytime and night-time acid secretion. According to data provided by the medication manufacturer, taking omeprazole 20mg can result in a mean reduction of at least 80% in 24-hour stomach acidity for individuals who take it regularly to manage a duodenal ulcer.

However, omeprazole works best when taken daily. After 4 days of consistent daily use, omeprazole reaches its maximum effect. This is because acid secretion depends on the dose of omeprazole in the blood over time, not the drug concentration at any given moment. If your prescriber recommends it, you can take certain antacids alongside omeprazole while you wait for it to take full effect. You can find more information about how long Omeprazole takes to work in our dedicated article. 

How Effective is Omeprazole for Heartburn?

Omeprazole has an extensive clinical evidence base and is widely regarded as one of the most effective treatments for acid-related conditions. In a landmark placebo-controlled trial, 81% of patients taking omeprazole showed measurable tissue healing after just four weeks, compared with only 6% in the placebo group. Your prescriber will determine the most appropriate dose based on your individual condition and symptom severity.

Omeprazole has also been shown to consistently outperform other acid-reducing medications such as H2 blockers. In a double-blind randomised controlled trial comparing omeprazole with ranitidine, healing rates after four weeks were 76% for omeprazole versus 27% for ranitidine, rising to 88% versus 38% after eight weeks.

A 2024 systematic review and meta-analysis concluded that omeprazole remains an effective and well-tolerated treatment for acid peptic disorders. It was significantly superior to placebo in relieving heartburn and was equivalent to other PPIs (such as pantoprazole and lansoprazole) in heartburn control and ulcer or erosion healing.

How To Take Omeprazole

You can take omeprazole capsules with or without food. Swallow the capsules whole with half a glass of water. Do not crush or chew them, as the gastro-resistant coating protects the pellets from stomach acid and helps ensure the medicine is released correctly. If you have difficulty swallowing capsules, you may open them and swallow the contents with water or mix them with still water or an acidic fruit juice. Take the prepared mixture straight away or within 30 minutes and do not chew or crush the pellets.

You may be prescribed omeprazole once or twice a day. Take it in the morning, and again in the evening if you take it twice a day. Try to take it at the same time every day. You may be prescribed other medicines to take alongside omeprazole for certain conditions. Take all medications exactly as directed and complete the full course, even if symptoms improve before it ends. 

When to Take Omeprazole

The best time to take omeprazole is 30 to 60 minutes before breakfast, when proton pumps are most receptive to the medication. If you struggle to take medication on an empty stomach, it will still work if you take it with food. Try to take omeprazole at the same time each day. 

If prescribed twice daily (such as during H. pylori treatment), take the second dose before your evening meal, about 10-12 hours after the first dose.

Omeprazole Dosage Information

Your clinician will determine a suitable starting dose of omeprazole and how often you should take it. Always follow the prescription when taking the medication.

Omeprazole capsules are available in several dosage strengths:

• Omeprazole 10 mg: may be used as a maintenance dose once symptoms of GORD have resolved and damage to the gullet has been repaired, where clinically appropriate.  
• Omeprazole 20 mg: the standard adult dose for treating GORD symptoms, gastric and duodenal ulcers, and as part of H. pylori eradication regimens (alongside antibiotics). Also available over the counter for short-term heartburn relief.
• Omeprazole 40 mg: prescribed for more severe cases of GORD, erosive oesophagitis that has not responded to 20 mg, or conditions involving pathological hypersecretion such as Zollinger-Ellison syndrome (higher doses may also be used).

What If I Forget to Take Omeprazole?

If you miss a dose of omeprazole, take it as soon as you remember, unless your next dose is due within a few hours, in which case, skip it and continue as normal. Never take a double dose. Regularly forgetting to take omeprazole may lead to a return of acid reflux symptoms. 

If You Take Too Many Omeprazole Capsules

If you take more omeprazole capsules than your clinician prescribed, seek medical attention from your doctor or pharmacist straight away. If you go to hospital, take the medication and the enclosed Patient Information Leaflet with you. 

If You Stop Taking Omeprazole

Do not stop taking omeprazole capsules without speaking to your clinician or doctor first. Stopping omeprazole can lead to a return of acid reflux symptoms. If gastro-oesophageal tissue has not had time to fully heal, symptoms may even worsen. Your prescriber will recommend how long to take omeprazole and will regularly review your treatment progress. 

Omeprazole Side Effects and Cautions

Before taking omeprazole for the first time, you should be aware of potential risks and side effects that you may experience. If you have any concerns about taking omeprazole, seek advice from your prescriber. 

Potential Side Effects with Omeprazole 

As with any medication, omeprazole can cause unwanted side effects. If you experience side effects, contact your prescriber for advice. The following have been reported with omeprazole use:

Please note that the table above does not include a complete list of possible omeprazole side effects. More details are in the Patient Information Leaflet that comes with the medication. If you experience any adverse reactions, you can report them to your clinician or via the MHRA’s Yellow Card Scheme. 

Side Effects of Long-Term Use of Omeprazole 

Whilst omeprazole can be taken long-term, there is an increased risk of certain side effects if you take it for more than three months. Your blood magnesium levels may fall, leading to fatigue, involuntary muscle contractions, disorientation, convulsions, dizziness, or an increased heart rate. Tell your prescriber if you experience any of these symptoms. Low magnesium levels can also reduce potassium or calcium levels. If you take omeprazole for more than three months, you may need regular blood tests to monitor your magnesium levels.

Taking a proton pump inhibitor like omeprazole capsules, especially over a period of more than one year, may slightly increase your risk of fracture in the hip, wrist or spine. Tell your doctor if you have osteoporosis or if you are taking corticosteroids (which can increase the risk of osteoporosis).

Serious Omeprazole Side Effects

Serious side effects associated with omeprazole are rare (up to 1 in 1,000 people) or very rare (up to 1 in 10,000 people). If you experience any of the following, stop taking omeprazole and seek immediate medical attention:

• A severe allergic reaction (sudden wheezing, swelling of your lips, tongue and throat or body, rash, fainting or difficulties in swallowing)
• Stevens-Johnson syndrome or toxic epidermal necrolysis (reddening of the skin with blisters or peeling)
• DRESS syndrome or drug hypersensitivity syndrome (widespread rash, fever, and enlarged lymph nodes)
• Acute generalised exanthematous pustulosis (a red, scaly widespread rash with bumps under the skin and blisters accompanied by fever)
• Yellow skin, dark urine, and tiredness, which can be symptoms of liver problems. 

Omeprazole Warnings and Interactions

Omeprazole may not be suitable for everyone. Before you are prescribed omeprazole for the first time, your clinician will review your medical history to determine whether it is right for you.

Do not use omeprazole capsules if you are:

• Allergic to omeprazole or any other ingredient listed in the medication 
• Allergic to medicines containing proton pump inhibitors (PPIs) 
• Taking a medicine containing nelfinavir (used to treat HIV)

Precautions Before Taking Omeprazole

Omeprazole may hide the symptoms of other diseases. If any of the following happen to you before you start taking omeprazole or during treatment, contact your prescriber immediately:

• You lose a lot of weight for no reason and have problems swallowing
• You get stomach pain or indigestion
• You begin to vomit food or blood
• You pass black stools
• You experience severe or persistent diarrhoea, as omeprazole capsules have been associated with a small increase in infectious diarrhoea
• You have severe liver problems
• You have ever had a skin reaction after treatment with a medicine similar to omeprazole capsules that reduces stomach acid
• You are due to have a specific blood test (Chromogranin A)

When taking omeprazole, kidney inflammation may occur. Signs and symptoms may include decreased volume of urine or blood in your urine and/or hypersensitivity reactions such as fever, rash, and joint stiffness. Tell your prescriber if any of these occur.

If you develop a rash, especially in sun-exposed areas, tell your doctor as soon as possible, as you may need to stop your omeprazole capsules. Remember to also mention any other side effects, such as joint pain.

This medicine may affect how your body absorbs vitamin B12, particularly if you need to take it for a long time. Contact your doctor if you notice any of the following symptoms, which could indicate low levels of Vitamin B12:

• Extreme tiredness or lack of energy
• Pins and needles
• Sore or red tongue, mouth ulcers
• Muscle weakness
• Disturbed vision
• Problems with memory, confusion, depression

Omeprazole and Other Medicines

Tell your prescriber if you are taking or have recently taken any other prescribed medicines, over-the-counter medications, herbal remedies, or supplements. Do not take omeprazole if you are taking nelfinavir (a medicine used to treat HIV). Tell your prescriber if you are taking any of the following:

• Ketoconazole, itraconazole, posaconazole, or voriconazole (antifungals)
• Digoxin
• Diazepam
• Phenytoin
• Medicines used to thin your blood (such as warfarin)
• Rifampicin
• Atazanavir
• Tacrolimus
• St John’s Wort 
• Cilostazol
• Saquinavir 
• Clopidogrel
• Erlotinib
• Methotrexate

Pregnancy and Breastfeeding

If you are pregnant, think you may be pregnant, or are breastfeeding, seek advice from your doctor before taking omeprazole. Omeprazole is excreted in breast milk but is not likely to affect a breastfed child when used at prescribed doses. Your prescriber can also help advise you on whether to take omeprazole while breastfeeding. 

Where Can I Buy Omeprazole in the UK?

In the UK, you can buy omeprazole from licensed pharmacies. Omeprazole 10mg, 20mg, and 40mg capsules are available with a prescription from an appropriately trained prescriber. A short course of omeprazole 20mg can also be bought over-the-counter.  

At Prescription Doctor, our highly trained clinicians will review your confidential online consultation to determine whether omeprazole is the right treatment for you. 

Can You Buy Omeprazole Over the Counter?

Only omeprazole 20mg can be bought over the counter in the UK. It is licensed for the short-term treatment of reflux symptoms such as heartburn and acid regurgitation. Use omeprazole 20mg for no more than 14 days, then seek advice from a clinician. If you have been taking omeprazole over-the-counter, tell your prescriber so they can assess your response to treatment. Long-term use of omeprazole may require additional monitoring and risk discussion. 

Is Omeprazole Available on the NHS?

NHS clinicians commonly prescribe omeprazole. In England, the standard prescription charge applies to all NHS prescriptions unless you have a valid exemption. NHS prescriptions in Scotland and Wales are free.

Many people find it more convenient to purchase medication through a reputable online pharmacy like Prescription Doctor. Our clinicians can review your symptoms and medical history without the need to wait for a GP appointment. 

Can You Buy Omeprazole Online?

Yes, you can buy omeprazole online from trusted pharmacies such as Prescription Doctor without needing an appointment. You can start a consultation anytime from the comfort of your home and, if approved, your order is dispatched for discreet delivery to your door. It’s that straightforward.

Our team of specialist clinicians checks all orders to ensure your chosen medication is safe and suitable for your circumstances before passing them to our General Pharmaceutical Council-registered pharmacy for dispatch in plain packaging. Orders approved before 3pm Monday to Friday are also eligible for next-day delivery. 

Frequently Asked Questions About Omeprazole Capsules