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Proton Pump Inhibitor — Obstetric Pregnancy: §4.6, verbatim: 'Pregnancy — Results from three prospective epidemiological studies (more than 1 000 exposed outcomes) indicate no adverse effects of omeprazole on pregnancy or on the health of the foetus/newborn child. Omeprazole can be used during pregnancy. Breast-feeding — Omeprazole is excreted in breast milk but is not likely to influence the child when therapeutic doses are used. Fertility — Animal studies with the racemic mixture omeprazole, given by oral administration do not indicate effects with respect to fertility.'

Omeprazole (GORD / Hyperemesis in Pregnancy)

Brand names: Losec, Prilosec

Omeprazole is a proton pump inhibitor used in pregnancy to treat gastro-oesophageal reflux disease and acid-related symptoms, and as adjunctive acid suppression in hyperemesis gravidarum.

Adult dose

Dose: GORD / REFLUX OESOPHAGITIS ONLY — this is not a hyperemesis gravidarum regimen (see notes): 20 mg once daily by mouth. §4.2, 'Treatment of symptomatic gastro-oesophageal reflux disease', verbatim: 'The recommended dose is Losec 20 mg daily. Patients may respond adequately to 10 mg daily, and therefore individual dose adjustment should be considered. If symptom control has not been achieved after four weeks treatment with Losec 20 mg daily, further investigation is recommended.' Where there is proven reflux oesophagitis, §4.2 verbatim: 'The recommended dose is Losec 20 mg once daily. In most patients healing occurs within four weeks. For those patients who may not be fully healed after the initial course, healing usually occurs during a further four weeks treatment period. In patients with severe oesophagitis Losec 40 mg once daily is recommended and healing is usually achieved within eight weeks.' Long-term management of healed reflux oesophagitis, verbatim: 'the recommended dose is Losec 10 mg once daily. If needed, the dose can be increased to Losec 20 mg to 40 mg once daily.' This label states NO pregnancy-specific dose and no dose modification for pregnancy — §4.6 says only: 'Omeprazole can be used during pregnancy.'
Route: Oral — Losec 10 mg enteric-coated capsules. §4.2 Method of administration, verbatim: 'It is recommended to take Losec capsules in the morning, swallowed whole with half a glass of water. The capsules must not be chewed or crushed.' For swallowing difficulties, verbatim: 'Patients can open the capsule and swallow the contents with half a glass of water or after mixing the contents in a slightly acidic fluid e.g. fruit juice or applesauce, or in non-carbonated water. Patients should be advised that the dispersion should be taken immediately (or within 30 minutes) and always be stirred just before drinking and rinsed down with half a glass of water. Alternatively, patients can suck the capsule and swallow the pellets with half a glass of water. The enteric-coated pellets must not be chewed.' SCOPE: no intravenous omeprazole label was fetched, so the page's 'Intravenous' route is not sourced and no IV dose is published.
Frequency: Once daily. §4.2 method of administration: take the capsules in the morning.
SCOPE — WHAT IS AND IS NOT SOURCED: the dose above is the SPC's general adult GORD / reflux-oesophagitis regimen, which is this page's primary indication; it is not a pregnancy-specific dose, because this label states none. HYPEREMESIS GRAVIDARUM IS NOT DOSED BY THIS SOURCE. || USE IN PREGNANCY, §4.6 verbatim: 'Results from three prospective epidemiological studies (more than 1 000 exposed outcomes) indicate no adverse effects of omeprazole on pregnancy or on the health of the foetus/newborn child. Omeprazole can be used during pregnancy.' Breast-feeding, verbatim: 'Omeprazole is excreted in breast milk but is not likely to influence the child when therapeutic doses are used.' || WHY maxDose IS EMPTY: no maximum daily dose is stated for these indications. The 60–120 mg figures in §4.2 belong to Zollinger-Ellison syndrome, a different indication, and are deliberately not used as this page's ceiling. A separate interaction-specific cap (§4.4, an eligibility rule rather than this dose's ceiling): if atazanavir plus a PPI is unavoidable, 'omeprazole 20 mg should not be exceeded.'

Dose adjustments

Renal

§4.2 Special populations, under the heading 'Renal impairment', verbatim: 'Dose adjustment is not needed in patients with impaired renal function (see section 5.2).'

Hepatic

§4.2 Special populations, under the heading 'Hepatic impairment', verbatim: 'In patients with impaired hepatic function a daily dose of 10 mg to 20 mg may be sufficient (see section 5.2).' Note the label frames this as a dose that 'may be sufficient', NOT as a stated maximum.

Dose independently re-sourced from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — clinician-reviewed. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

  • §4.3, verbatim and complete: 'Hypersensitivity to the active substance, substituted benzimidazoles or to any of the excipients listed in section 6.1.'
  • §4.3, verbatim and complete: 'Omeprazole like other proton pump inhibitors (PPIs) must not be used concomitantly with nelfinavir (see section 4.5).'
  • Not a §4.3 contraindication but a §4.4 'not recommended': 'Co-administration of atazanavir with proton pump inhibitors is not recommended (see section 4.5). If the combination of atazanavir with a proton pump inhibitor is judged unavoidable, close clinical monitoring (e.g. virus load) is recommended in combination with an increase in the dose of atazanavir to 400 mg with 100 mg of ritonavir; omeprazole 20 mg should not be exceeded.'
  • Not a §4.3 contraindication but a §4.4 precaution: 'As a precaution, concomitant use of omeprazole and clopidogrel should be discouraged.'
  • Not a §4.3 contraindication but a §4.4 diagnostic caution: 'In the presence of any alarm symptom (e.g. significant unintentional weight loss, recurrent vomiting, dysphagia, haematemesis or melena) and when gastric ulcer is suspected or present, malignancy should be excluded, as treatment may alleviate symptoms and delay diagnosis.'
  • INCOMPLETE LIST WARNING: §4.4 was truncated at the source-fetch limit, so any further bars or precautions stated after the fracture-risk paragraph were not retrieved.

Side effects

  • §4.8 summary, verbatim: 'The most common side effects (1 to 10% of patients) are headache, abdominal pain, constipation, diarrhoea, flatulence and nausea/vomiting.'
  • Common (≥1/100 to <1/10), §4.8: headache; abdominal pain, constipation, diarrhoea, flatulence, nausea/vomiting, fundic gland polyps (benign)
  • Uncommon (≥1/1,000 to <1/100), §4.8: insomnia; dizziness, paraesthesia, somnolence; vertigo; increased liver enzymes; dermatitis, pruritus, rash, urticaria; fracture of the hip, wrist or spine
  • Rare (≥1/10,000 to <1/1,000), §4.8: leukopenia, thrombocytopenia; hypersensitivity reactions e.g. fever, angioedema and anaphylactic reaction/shock; hyponatraemia; agitation, confusion, depression; taste disturbance; blurred vision; bronchospasm; dry mouth, stomatitis, gastrointestinal candidiasis; hepatitis with or without jaundice; alopecia, photosensitivity, acute generalized exanthematous pustulosis (AGEP), drug reaction with eosinophilia and systemic symptoms (DRESS); arthralgia, myalgia; tubulointerstitial nephritis (with possible progression to renal failure)
  • Very rare (<1/10,000), §4.8: agranulocytosis, pancytopenia; aggression, hallucinations; hepatic failure, encephalopathy in patients with pre-existing liver disease; muscular weakness; erythema multiforme, Stevens-Johnson syndrome, toxic epidermal necrolysis (TEN)
  • Not known, §4.8: 'Hypomagnesaemia; severe hypomagnesaemia may result in hypocalcaemia. Hypomagnesaemia may also be associated with hypokalaemia.'; microscopic colitis; subacute cutaneous lupus erythematosus
  • §4.4/§4.8, verbatim: 'Severe cutaneous adverse reactions (SCARs), including Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), drug reaction with eosinophilia and systemic symptoms (DRESS) and acute generalized exanthematous pustulosis (AGEP) have been reported in association with omeprazole treatment.'
  • INCOMPLETE LIST WARNING: §4.8 was truncated at the source-fetch limit part-way through the 'Reproductive system and...' system organ class, so the tail of the adverse-reaction table was not retrieved.

Monitoring

  • Magnesium — §4.4, verbatim: 'Severe hypomagnesaemia has been reported in patients treated with proton pump inhibitors (PPIs) like omeprazole for at least three months, and in most cases for a year... For patients expected to be on prolonged treatment or who take PPIs with digoxin or drugs that may cause hypomagnesaemia (e.g. diuretics), healthcare professionals should consider measuring magnesium levels before starting PPI treatment and periodically during treatment.'
  • Vitamin B12 — §4.4, verbatim: 'Omeprazole, as all acid-blocking medicines, may reduce the absorption of vitamin B 12 (cyanocobalamin) due to hypo- or achlorhydria. This should be considered in patients with reduced body stores or risk factors for reduced vitamin B 12 absorption on long-term therapy.'
  • Fracture risk — §4.4, verbatim: 'Proton pump inhibitors, especially if used in high doses and over long durations (> 1 year), may modestly increase the risk of hip, wrist and spine fracture, predominantly in the elderly or in presence of other recognised risk factors. Observational studies suggest that proton pump inhibitors may increase the overall risk of fracture by 10 to 40%... Patients at risk of osteoporosis should receive care according to current clinical guidelines.'
  • CYP2C19 interactions — §4.4, verbatim: 'Omeprazole is a CYP2C19 inhibitor. When starting or ending treatment with omeprazole, the potential for interactions with drugs metabolised through CYP2C19 should be considered.'
  • Exclude malignancy in the presence of alarm symptoms before attributing them to acid disease (§4.4, quoted in full under contraindications).
  • INCOMPLETE LIST WARNING: §4.4 was truncated at the source-fetch limit; any further monitoring advice beyond the fracture paragraph was not retrieved.

Clinical monograph

How it works

It irreversibly inhibits the gastric H+/K+-ATPase (proton pump) in parietal cells, markedly reducing basal and stimulated gastric acid secretion.

Prescribing in practice

  • Omeprazole has a reassuring safety record in pregnancy and is used when lifestyle measures and antacids or alginates are insufficient.
  • It may mask the symptoms of, and rarely delay diagnosis of, underlying gastric malignancy, so alarm features warrant investigation.
  • It interacts with several drugs, notably reducing the activation of clopidogrel and affecting agents whose absorption depends on gastric acidity.

Monitoring

Routine monitoring is not usually required; review symptom control and consider magnesium and B12 with prolonged use.

Counselling the patient

  • Take it before food, typically in the morning.
  • Continue lifestyle measures such as smaller meals and avoiding late eating.
  • Report difficulty swallowing, vomiting blood or unintended weight loss.

Evidence & guidelines

Proton pump inhibitors including omeprazole are recommended where simpler measures fail for reflux in pregnancy, supported by reassuring observational safety data.

Reference: RCOG Green-top 69 (Hyperemesis Gravidarum 2024); NICE NG201; Pasternak & Hviid (2010) Danish cohort; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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