Antihistamine + vitamin B6 (NVP) Pregnancy: Intended for use in pregnant women. A large amount of data on pregnant women, including two meta-analyses with over 168,000 patients and 18,000 exposures to the doxylamine/pyridoxine combination during the first trimester, indicates no malformative nor feto/neonatal toxicity. Breast-feeding: the molecular weight of doxylamine succinate is low enough that passage into breast milk can be expected, and excitement, irritability and sedation have been reported in nursing infants presumably exposed through breast milk; infants with apnoea or other respiratory syndromes may be particularly vulnerable to the sedative effects. Pyridoxine hydrochloride is excreted into breast milk with no reported adverse events in exposed infants. A risk to breastfed infants cannot be excluded — a decision must be made whether to discontinue breast-feeding or to discontinue/abstain from therapy.

Doxylamine with pyridoxine

Brand names: Xonvea

Doxylamine with pyridoxine is a fixed combination of a sedating antihistamine and vitamin B6 used to treat nausea and vomiting of pregnancy.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Starting dose two tablets at bedtime on Day 1 (total 20 mg doxylamine succinate / 20 mg pyridoxine hydrochloride). If this adequately controls symptoms the next day, continue two tablets at bedtime. If symptoms persist into the afternoon of Day 2, continue two tablets at bedtime on Day 2 and from Day 3 take three tablets daily (one tablet in the morning and two tablets at bedtime). If three tablets do not adequately control symptoms on Day 3, take four tablets daily from Day 4 (one tablet in the morning, one tablet mid-afternoon and two tablets at bedtime)

Route: Oral — administer on an empty stomach with a glass of water; gastro-resistant tablets should be swallowed whole and must not be crushed, split or chewed

Frequency: Daily, titrated as above: two at bedtime, increasing to morning plus bedtime, then morning plus mid-afternoon plus bedtime

Max: Four tablets daily (one in the morning, one in the mid-afternoon and two at bedtime)

Fetched label is 'Xonvea 10 mg/10 mg gastro-resistant tablets' (UK SPC) — a fixed combination of doxylamine succinate 10 mg with pyridoxine hydrochloride 10 mg per tablet, for nausea and vomiting of pregnancy. Should be taken as a daily prescription and NOT on an as-needed basis. Continued need should be reassessed as the pregnancy progresses. To prevent a sudden return of nausea and vomiting of pregnancy symptoms, a gradual tapering dose is recommended at the time of discontinuation. There is limited evidence for the combination in hyperemesis gravidarum — these patients should be treated by a specialist. May cause somnolence due to the anticholinergic properties of doxylamine; use is not recommended if a woman is concurrently using CNS depressants including alcohol. Use with caution in asthma, increased intraocular pressure, narrow angle glaucoma, stenosing peptic ulcer, pyloroduodenal obstruction and bladder-neck obstruction. Contains pyridoxine hydrochloride (a vitamin B6 analogue), so additional levels from diet and vitamin B6 supplements should be assessed. False positive urine screening tests for methadone, opiates and phencyclidine (PCP) have been reported. The fetched US openFDA record was a single-ingredient doxylamine OTC 'Sleep Aid' product and was NOT used — it is a different product and indication. Paediatric (non per-kg, so not expressed as a mg/kg dose): not indicated for use in children under 18 years of age; safety and efficacy have not been established in that population and no data are available. Verify any under-18 use against a children's formulary.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Hypersensitivity to doxylamine succinate, other ethanolamine-derivative antihistamines, pyridoxine hydrochloride or any of the excipients
Concomitant use with monoamine oxidase inhibitors (MAOIs)

Side effects

Somnolence (very common)
Dizziness (common)
Dry mouth (common)
Fatigue (common)
Headache, migraine, paraesthesia, psychomotor hyperactivity (frequency not known)
Blurred vision and visual disturbances; dysuria and urinary retention; palpitation and tachycardia (frequency not known)

Interactions

Monoamine oxidase inhibitors (MAOIs) — prolong and intensify the anticholinergic effects of antihistamines; concomitant treatment is contraindicated
CNS depressants including alcohol, hypnotic sedatives and tranquillisers — concurrent use is not recommended; the combination may result in severe drowsiness
Food — a food-effect study showed that the delay in onset of action may be further delayed and absorption reduced when tablets are taken with food; take on an empty stomach with a glass of water
Urine drug screening — false positive urine drug screens for methadone, opiates and PCP can occur; confirmatory tests such as GC-MS should be used to confirm the identity of the substance after a positive immunoassay

Clinical monograph

How it works

Doxylamine is an H1-antihistamine with antiemetic and sedative properties, while pyridoxine (vitamin B6) is thought to contribute an additional antiemetic effect; the combination relieves pregnancy-related nausea.

Prescribing in practice

Warn that the doxylamine component is sedating and may impair the ability to drive or operate machinery, with additive effects when combined with alcohol or other CNS depressants.
It is generally used when conservative measures fail to control nausea and vomiting of pregnancy.
Avoid concurrent use with monoamine oxidase inhibitors and use caution in conditions where antimuscarinic effects are problematic, such as narrow-angle glaucoma.

Monitoring

Routine laboratory monitoring is not required; review symptom control and degree of sedation and reassess if vomiting is severe or persistent.

Counselling the patient

Drowsiness is common, so avoid driving or operating machinery until you know how it affects you.
Avoid alcohol while taking this medicine.
Seek urgent review if you cannot keep fluids down or show signs of dehydration.

Evidence & guidelines

A modified-release doxylamine-pyridoxine combination is supported for nausea and vomiting of pregnancy and is reflected in UK guidance on managing this condition.

Reference: RCOG GTG 69; NICE CKS NVP; SmPC; 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).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways