Omeprazole Side Effects: What to Expect & When to See a Doctor

What you need to know

Omeprazole is a proton pump inhibitor (PPI) available over the counter as Pyrocalm Control 20mg, licensed for short-term self-treatment of reflux symptoms like heartburn and acid regurgitation in adults. Most people tolerate it well, but like all medicines it can cause side effects — this guide covers what to expect, what's common, and when to stop taking it and speak to a pharmacist or doctor. If you're still weighing up which product to use, our indigestion and heartburn relief guide covers product choice in more depth.

How long can I take omeprazole for over the counter?

Pyrocalm Control 20mg is for the short-term treatment of reflux symptoms such as heartburn and acid regurgitation in adults, taken as one 20mg tablet a day for up to 14 days. It can take 2–3 consecutive days to feel the benefit. Once symptoms ease, treatment should be stopped — it isn't licensed for ongoing, preventative use. It's also available as a pack of 14 for a full course.

Common side effects

The most common side effects are abdominal pain, constipation, diarrhoea, wind, nausea or vomiting, and headache. Benign stomach polyps have also been reported at this frequency.

Less common and rarer side effects

• Uncommon: dizziness, tingling sensations (paraesthesia), drowsiness, insomnia, skin reactions (dermatitis, itching, rash, hives), swollen feet or ankles, raised liver enzymes, and an increased risk of bone fracture with longer-term or higher-dose use.
• Rare: reduced blood cell counts, low sodium levels, agitation, confusion, depression, altered taste, blurred vision, wheezing or bronchospasm, dry mouth, oral thrush, hair loss, a photosensitivity (sun-sensitive) rash, joint or muscle pain, kidney inflammation, and excessive sweating.
• Very rare: aggression, hallucinations, severe liver problems, brain inflammation in those with pre-existing severe liver disease, a severe skin reaction (erythema multiforme), muscle weakness, and, in men, enlarged breast tissue.

Serious side effects to be aware of

A small number of more serious risks are linked to longer-term use: low vitamin B12 (which can cause tiredness, dizziness, or muscle twitches/weakness), weakened bones that fracture more easily, and — rarely — a lupus-like reaction causing rashes and joint pain. This risk increases with long-term use of a year or more, which is one reason the OTC licence limits self-treatment to 14 days before a doctor's involvement is needed.

When to speak to a pharmacist or doctor before taking it

Check with a doctor first if you:

• have had a previous stomach ulcer or gastrointestinal surgery
• have been treating indigestion or heartburn continuously for 4 weeks or more
• have jaundice or severe liver disease
• are due to have a specific blood test (Chromogranin A) or an endoscopy
• have poor vitamin B12 absorption
• have unexplained weight loss together with difficulty swallowing
• are vomiting food or blood, or passing black stools
• have severe or persistent diarrhoea
• are aged over 55 with new or recently changed symptoms

When to seek urgent help

Call 111 if you're taking omeprazole and think you might be having serious side effects, or if you have taken more than the packet, leaflet or prescription states. Seek emergency help for signs of a serious allergic reaction — a swollen throat or tongue, a raised itchy rash, or difficulty breathing.

Who shouldn't take it

Don't take Pyrocalm Control if you're allergic to omeprazole, another proton pump inhibitor, or any of the tablet's ingredients, or if you're taking the HIV medicine nelfinavir. It isn't licensed for children or adolescents under 18.