Sounds like 'oh-MEP-ra-zol'

Omeprazole is used to treat problems affecting your stomach and gut, such as indigestion, reflux and ulcers. Find out how to take it safely and the possible side effects.

Type of medicine Also called
  • Omeprazole Actavis
  • Losec®

What is omeprazole?

Omeprazole reduces the amount of acid produced in your stomach. It belongs to a group of medicines known as proton pump inhibitors (PPIs). They are used to treat conditions associated with high levels of stomach acid, such as indigestion, reflux and ulcers. Omeprazole can prevent ulcers from forming or help the healing process where damage has already occurred.

Omeprazole can be used to prevent ulcers caused by medicines such as non-steroidal anti-inflammatory drugs (NSAIDs). Examples of NSAIDs are diclofenac, ibuprofen, and naproxen.

Omeprazole can also be given together with antibiotics to get rid of Helicobacter pylori, a bacteria found in your stomach that can cause ulcers. 

How is omeprazole available?

In Aotearoa New Zealand omeprazole is available as oral (taken by mouth) capsules, tablets or liquid. Omeprazole also be given as an injection in hospital. This page focuses on oral omperazole.

All types of omeprazole are available on prescription from your doctor. You can also buy a short course of omeprazole tablets or capsules from a pharmacy after speaking with a pharmacist. The pharmacist will ask you some questions to make sure it is safe for you to take it.


  • The usual dose of omeprazole is 20 mg a day.
  • For some people 10 mg a day is enough, while others may need a higher dose of 40 mg a day.
  • It is best to take the lowest effective dose for the shortest possible time.
  • Your healthcare team will advise you on how long to take omeprazole for (usually for 4–8 weeks). Some people may need to take it for longer.
  • The pharmacy label on your medicine will tell you how much omeprazole to take, how often to take it and any special instructions including how to store it.

Precautions before starting omeprazole

  • Are you pregnant, planning a pregnancy or breastfeeding?
  • Do you have problems with your liver?
  • Are taking any other medicines? This includes any medicines you are taking that you can buy without a prescription, as well as herbal and complementary medicines.

If you answered yes to any of these questions, it’s important that you tell your doctor or pharmacist before you start omeprazole. Sometimes a medicine isn’t suitable for a person with certain conditions or it can only be used with extra care.

How to take omeprazole

  • Timing: Take omeprazole at the same time each day, usually in the morning. Omeprazole is usually taken once a day, but some people may need to take it twice a day. Your doctor will tell you how often to take it. Omeprazole can be taken before or after food, although taking it before food is best.
  • Swallow the capsule whole with a glass of water (200-250 mLs). Do not crush or chew the capsules– the medicine doesn't work properly if the capsule is crushed or chewed. If you have difficulty swallowing the capsule, you can open it and sprinkle the pellets over some fruit juice or yoghurt and swallow the pellets without chewing.
  • Shake liquid well before use. When measuring the dose of liquid omeprazole, measure the right amount using an oral syringe or medicine spoon. You can get these from your pharmacy. Do not use a kitchen spoon as it will not give you the right amount.
  • Omeprazole starts to work within 2–3 days, but it may take up to 4 weeks for it to work fully.
  • Missed dose: If you forget to take your dose, take it as soon as you remember. But if it is nearly time for your next dose, just take the next dose at the right time. Do not take double the dose.

Precautions while you are taking omeprazole

Avoid long-term use of omeprazole

If you don’t need them, PPIs like omeprazole should not be taken long term, because of the possible side effects. There may be a small increased risk of bone fractures, chest infections, kidney problems and nutrient deficiencies such as low magnesium and vitamin B12

If you’ve been taking omeprazole for reflux for longer than 4–8 weeks, and your symptoms seem to be well managed, it’s a good idea to talk to your healthcare provider about reviewing your medicine. They may recommend stepping down your treatment. This could include:

  • Reducing your daily dose of omeprazole.
  • Taking omeprazole only when you experience the symptoms of heartburn and reflux (also known as on-demand therapy).
  • Stopping treatment completely, as your symptoms may not return. It may be best to reduce the dose over a few weeks before stopping.

Read more about PPIs for heartburn and reflux.

Avoid alcohol

Alcohol can make your stomach produce more acid than normal. This irritates the stomach lining and can make your symptoms worse. It's best to avoid alcohol if possible while you're taking omeprazole.


Omeprazole may interact with a few medicines and herbal supplements, so check with your doctor or pharmacist before starting any new medicines.

Possible side effects

Like all medicines omeprazole can cause side effects, although not everyone gets them. Often side effects improve as your body adjusts to the new medicine.

Rebound acid secretion when stopping

When omeprazole is stopped, a common side effect is rebound acid secretion, where the acid secretion in your stomach increases significantly. This should return to normal within 2 weeks. Because the symptoms of rebound acid secretion are the same as for reflux (such as indigestion, discomfort and pain in your upper stomach and chest, feeling sick and an acid taste in your mouth), it can form an ongoing loop where stopping omeprazole treatment creates the need to start it again.

Rather than restarting omeprazole, your doctor may advise you to use medicines that contain both an antacid and an anti-foaming agent, such as Acidex oral liquid or Gaviscon Double Strength tablets. These can be effective for treating rebound acid secretion. You can use these medicines to relieve the symptoms when they occur.

Talk to your doctor or pharmacist about how to manage rebound acid secretion.

Other side effects

Side effects What should I do?
  • Stomach upset, feeling sick
  • Feeling bloated, gas in your abdomen (tummy)
  • Loose stool (mild diarrhoea)
  • Constipation
  • These are quite common when you first start taking omeprazole.
  • If you feel sick, try taking omeprazole with or after a meal or snack. It may also help if you avoid eating rich or spicy food.
  • Tell your doctor if these side effects bother you.
  • Worsening stomach problems, such as really bad stomach pain, blood in your stool (poo) or black stools, vomiting blood or dark-coloured vomit
  • Tell your doctor immediately or phone Healthline 0800 611 116.
  • Signs of low magnesium, such as muscle cramps, weakness, tiredness, feeling irritable and changes in your heartbeat
  • Increase your intake of magnesium-rich foods such as wholegrain cereals, green leafy vegetables (spinach, parsley, cabbage), peas, lean meats, nuts, seeds and bananas.
  • Tell your doctor if these side effects bother you – you may need a magnesium supplement.
  • Severe diarrhoea (loose, watery, frequent stools)  
  • Omeprazole can increase the chance of getting severe diarrhoea (which may be caused by bacteria called clostridium difficile).
  • Stop omeprazole and tell your doctor immediately.
  • Signs of an allergic reaction such as rash, fever, painful joints
  • Tell your doctor immediately or phone Healthline 0800 611 116. 
For more information on side effects, see the consumer information leaflets below. 

Did you know that you can report a medicine side effect to the Centre for Adverse Reactions Monitoring (CARM)? Report a side effect to a product.

Learn more

The following links have more information on omeprazole:

Omeprazole Patient Information (Māori) NZ Formulary, NZ
Omeprazole Consumer Information TEVA


  1. Omeprazole NZ Formulary, NZ
  2. Omeprazole NHS, UK
  3. Stopping proton pump inhibitors in older people BPAC, NZ 
  4. Proton pump inhibitors – when is enough, enough? BPAC, NZ
  5. Proton pump inhibitors and the risk of acute kidney injury. BPAC, NZ

Additional resources for healthcare professionals

Omeprazole Actavis Medsafe, NZ
Extemporaneous formula standard batch sheet Omeprazole suspension 2 mg/mL NZ Formulary, NZ
Interaction – methotrexate and proton pump inhibitors Medsafe, NZ
Hypomagnesaemia – a risk associated with all proton pump inhibitors Medsafe, NZ
Proton pump inhibitors and interstitial nephritis Medsafe, NZ
Hypomagnesaemia with proton pump inhibitors BPAC, NZ, 2013
Managing dyspepsia and heartburn in general practice – an update BPAC, NZ, 2011
Clinical audit – identifying patients who may benefit from “stepping down” PPI treatment BPAC, NZ, 2016

Credits: Sandra Ponen, Pharmacist. Reviewed By: Maya Patel, MPharm PGDipClinPharm, Auckland Last reviewed: 01 Mar 2022