Anyone using the medicine for their stomach problems needs to know about four ‘serious’ side effects
Charlotte Smith Senior Lifestyle Content Editor
14:17, 22 Jan 2026
People taking the medication should be aware of the side effects (stock image)(Image: Getty)
The NHS website has a lot of helpful information for anyone worried about their health or taking specific medications. It’s always a good idea to read the leaflet that comes with your medicine, but it’s also smart to check the latest guidance from the NHS.
One medication that is often prescribed in the UK is omeprazole, which is a proton pump inhibitor (PPI) that helps lower the acid in your stomach. Doctors usually give it to patients who have stomach issues like acid reflux, heartburn, and indigestion.
There are some versions you can buy at the pharmacy without a prescription, but those can only be used for a couple of weeks, while most types need a prescription. Omeprazole can also help treat gastro-oesophageal reflux disease (GORD) and a stomach infection called Helicobacter pylori, but it needs to be taken with antibiotics.
Omeprazole is usually taken once daily, often in the morning, with or without food; capsules can sometimes be opened and mixed with soft food. It can take a few days to feel full relief from pain. Treatment length varies and depends on how long your doctor thinks you’ll need it for.
Like many other medications, omeprazole has side effects. Some of which are more common than others, and there are a few serious ones that people should know about.
What are the common side effects of omeprazole?a headachestomach painfeeling sick or being sickconstipation or diarrhoeafarting more than usual
The NHS explains: “Omeprazole will not usually affect your ability to drive, ride a bike or use machinery. But if you feel dizzy or have problems with your vision after taking it, wait until you no longer have these side effects.”
If you have any side effects that are bothering you or just won’t go away, talk to a pharmacist or a doctor. “They may be able to give you advice about how you can reduce the side effects. Keep taking your medicine unless you’re advised not to,” the NHS says.
Most adults and children can take prescribed omeprazole(Image: )
What are the more serious side effects of omeprazole?
Although rare, omeprazole can occasionally cause more serious side effects. The NHS states: “The chance of getting serious side effects can be higher if you take omeprazole for a long time (a year or more)”.
having a very low level of vitamin B12weakened bonesan allergic reactionrashes and joint pain
A lack of vitamin B12 can lead to feelings of tiredness, dizziness, and even muscle twitches or weakness. If your bones are weak, you might be more likely to break them if you fall or get hurt.
At the same time, an allergic reaction known as anaphylaxis can cause symptoms such as a swollen throat or tongue, an itchy rash, or trouble breathing. Some medications can also trigger a type of lupus, which may cause rashes (especially on areas of the skin that get sun) and joint pain.
The chance of getting serious side effects can be higher if you take omeprazole for a long time(Image: )
The NHS guidance regarding these side effects includes calling 111 if “you’re taking omeprazole and think you might be having serious side effects”. It is important to keep in mind that these are not all the side effects of omeprazole. But, if you have any concerns, it is important to speak to a GP as soon as possible to get proper treatment or change your dosage.
For a full list, see the leaflet that comes with your medicine or search for your medicine on the electronic medicines compendium website. You can report any side effects you get on the Yellow Card website.