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 possible side effects. Omeprazole is also called Losec.

The colour of omeprazole capsules will be changing 
From 1 August 2021, the colour and packaging for omeprazole capsules will be changing. They are still made by the same company (Actavis) and the formulation remains the same.
  • Omeprazole 10 mg and 20 mg – the capsules and bottles for are changing.
  • Omeprazole 40 mg – the capsules remain the same, but the bottles will have a new look. 
Read more about omeprazole changes.

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 stomach acid affecting your stomach and gut, 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, 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. 

In New Zealand omeprazole is available as capsules and can be given as an injection in hospital.  


  • 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 doctor will advise you how long to take omeprazole for (usually for 4 to 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. 

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. Do not crush or chew – 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.
  • 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.

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 to 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 Choosing Wisely, NZ 

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 so, 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.

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 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 restart 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. Alternatively, ranitidine tablets could be used. 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.
  • Tell your doctor if troublesome.
  • 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 troublesome – 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 difficle).
  • 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. 
  • Worsening stomach problems, such as really bad stomach pain, blood in your stool or black stools, vomiting blood or dark-coloured vomit
  • Tell your doctor immediately or phone Healthline 0800 611 116.


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

Learn more

The following links have more information on omeprazole:

Omeprazole (Māori) NeZ Formulary Patient Information
Losec Medsafe Consumer Information Sheets, NZ


  1. Stopping proton pump inhibitors in older people BPAC, NZ 2019
  2. Proton pump inhibitors: When is enough, enough? BPAC, NZ, 2014
  3. Proton pump inhibitors and the risk of acute kidney injury. BPAC, NZ, 2016
  4. Omeprazole NZ Formulary
Credits: Sandra Ponen, Pharmacist. Reviewed By: Angela Lambie, Pharmacist, Auckland Last reviewed: 19 Feb 2019