Phenergan
✅ Nausea relief
✅ Vomiting prevention
✅ Allergy symptom relief
✅ Motion sickness treatment
✅ Sedation induction
Phenergan contains Promethazine.
✓ Medically reviewed by Morgan Ellis — Pharmacy Researcher · 8 years experience · Last reviewed: May 2026
Quick Answer
Phenergan is a brand of promethazine 10 mg — a first-generation H1 antihistamine with strong anticholinergic, antiemetic, and sedative action. Take one tablet 30–60 minutes before travel for motion sickness, or 10–20 mg every 4–6 hours for nausea / allergic symptoms (usual maximum 100 mg/day in adults). The 10 mg tablet is the milder, finer-titration option compared with the 25 mg Avimax tablet.
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How Phenergan works
Promethazine combines four mechanisms in one molecule: H1 antihistamine blockade reduces allergic symptoms; central anticholinergic action suppresses the vestibular nuclei that drive motion sickness; D2 dopamine antagonism in the chemoreceptor trigger zone provides direct antiemetic effect; and CNS H1/M1 occupancy produces dose-dependent sedation. Onset is around 20 minutes after an oral dose, peak effect at 1–2 hours, and duration of effect is 4–6 hours (sedation may persist longer in older adults).
Indications and dose
| Indication | Adult dose (10 mg tablets) | Notes |
|---|---|---|
| Motion sickness — prevention | 20 mg (2 tablets) 30–60 min before travel; repeat 10–20 mg every 6–8 hours if needed | Take ahead of travel — once nausea has started, oral absorption is blunted |
| Nausea / vomiting | 10–20 mg every 4–6 hours as needed | Maximum 100 mg/day; assess underlying cause |
| Allergic rhinitis / urticaria | 10–20 mg up to three times daily | Often a single 20 mg evening dose |
| Short-term sedation | 20–50 mg at bedtime | Not for long-term insomnia — tolerance and anticholinergic burden build |
| Children 5–10 years | 10–20 mg at night for allergy / motion sickness | Specialist advice in younger children |
Important — children under 2 years
Promethazine is contraindicated in children under 2 years of age. Fatal cases of respiratory depression have been reported. Use with caution in children aged 2–6 years and only at the lowest effective dose.
Side effects
Common (often dose-related): drowsiness, dry mouth, blurred vision, urinary hesitancy, mild constipation, dizziness on standing.
Less common: photosensitivity, paradoxical excitation in children, tinnitus, mild tachycardia.
Serious — seek urgent care: respiratory depression (especially in young children or with opioids/benzodiazepines), neuroleptic malignant syndrome (rigidity + fever + altered consciousness), acute dystonic reaction (oculogyric crisis, neck spasm — IV procyclidine reverses), severe orthostatic hypotension, seizures at high doses.
Contraindications and cautions
- Children under 2 years (absolute)
- Narrow-angle (closure) glaucoma
- Severe benign prostatic hyperplasia or symptomatic urinary retention
- Severe respiratory disease — especially when sedation may worsen ventilation
- Concurrent MAO inhibitors
- Older adults (Beers Criteria caution — anticholinergic burden, falls, delirium)
- Driving or operating machinery — strong sedation persists 6–12 hours
Drug interactions
| Interacting drug | Effect | Action |
|---|---|---|
| Opioids, benzodiazepines, barbiturates, alcohol | Additive CNS + respiratory depression | Avoid combination or reduce both doses |
| Other anticholinergics (TCAs, FGA antipsychotics, antiparkinson agents) | Additive dry mouth, retention, confusion | Avoid stacking; lower elderly dose |
| MAO inhibitors | Prolonged anticholinergic + sedative effect | Avoid; 14-day wash-out either side |
| Adrenaline (for hypotension) | Reverse vasopressor effect via alpha block | Use noradrenaline / phenylephrine instead |
| Levodopa | D2 antagonism reduces antiparkinson efficacy | Avoid in Parkinson disease — use ondansetron / domperidone |
| QT-prolonging drugs (azithromycin, quinine, amiodarone) | Additive QT signal at high doses | Caution; avoid at higher promethazine doses |
Pregnancy, breastfeeding and storage
Promethazine has a long real-world record of use in pregnancy (NVP and severe nausea) — historically classified low-risk but, like any medication, the lowest effective dose for the shortest course is preferred and a clinician should make the call. Small amounts pass into breast milk and may sedate the infant; short occasional use is generally acceptable, regular use less so. Store below 30 °C, protected from light.
Frequently Asked Questions
How long before travel should I take Phenergan?
Take 20 mg (two 10 mg tablets) about 30–60 minutes before departure. Once motion sickness has started, gastric stasis blunts oral absorption — better to take a second dose 6–8 hours later than to double-up if symptoms are already severe.
Phenergan 10 mg vs Avimax 25 mg — which should I pick?
Both are promethazine, just different strengths. The 10 mg tablet (Phenergan) is the better choice for evening allergy management, mild motion sickness, paediatric dosing (over age 2), and any situation where you need finer titration or less sedation. The 25 mg tablet (Avimax) is appropriate for short-haul travel where you do not need to drive at the destination, post-operative nausea, and adult doses where 10 mg has been insufficient.
Can I drive after taking Phenergan?
No. Even at 10 mg promethazine causes meaningful drowsiness and impairs reaction time for at least 6–12 hours. Combine that with alcohol or any sedating co-medication and the impairment is much worse. Plan around the dose.
Is Phenergan safe in children?
It is contraindicated below 2 years of age because of fatal respiratory depression in case reports. Use cautiously between 2 and 6 years and only at the lowest effective dose. Children over 5 commonly receive 10–20 mg for motion sickness or allergic urticaria.
Phenergan vs cetirizine or loratadine — what is the difference?
Cetirizine and loratadine are second-generation antihistamines designed to skip the brain — they relieve allergy without much sedation, but they have no antiemetic or vestibular effect. Promethazine is a first-generation drug that crosses freely into the brain — it sedates, it suppresses motion sickness, and it stops vomiting. Pick the second-generation drug for ordinary allergy and Phenergan when the sedation or antiemetic action is wanted.
Can I take Phenergan with my sleeping tablet or anxiolytic?
Phenergan adds significantly to the depression of breathing and consciousness produced by zolpidem, benzodiazepines, opioids, gabapentin or alcohol. The combination is not safe at standard doses. Discuss with the prescribing clinician before stacking it on top.
Will Phenergan help with vertigo?
It has some benefit in acute peripheral vertigo because of its anticholinergic vestibular suppression. For chronic Meniere’s disease or recurrent peripheral vertigo, betahistine (Vertin, Betavert, Betavert Tab) is the more appropriate agent. Promethazine is short-course only — long-term use slows the brain’s vestibular compensation.
Can I take Phenergan with food or alcohol?
Food is fine and may reduce stomach upset. Alcohol is not — it dramatically increases sedation, lowers blood pressure further, and impairs cognition far beyond either drug alone.
Is Phenergan safe in pregnancy?
It has been used in pregnancy for severe nausea and vomiting for many decades and is generally regarded as low risk, but no antiemetic should be taken without medical advice during pregnancy. First-line for nausea and vomiting of pregnancy is Doxinate (doxylamine + B6).
Why does Phenergan dry my mouth?
Promethazine’s anticholinergic action reduces saliva, tears and respiratory secretions. Useful for nausea but unpleasant for the mouth. Sip water, chew sugar-free gum, and avoid stacking with other anticholinergic drugs (TCAs, oxybutynin, hyoscine patches).
How do I store Phenergan?
Below 30 °C in its original pack, protected from light and moisture. Keep out of reach of children — even a small overdose in a young child can produce serious respiratory depression.
Travellers who find the 10 mg strength of Phenergan (promethazine) leaves residual nausea on long-haul flights or coach trips usually step up to the higher-dose sibling Avimax (promethazine 25 mg), taken 30 to 60 minutes before departure for stronger antihistamine antiemetic cover at double the per-tablet potency.
Other Travel Sickness Treatments
- Avimax (Promethazine 25 mg) — same molecule, higher strength
- Diligan (Meclizine 25 mg) — less sedating antihistamine
- Draminate (Dimenhydrinate 50 mg) — original Dramamine equivalent
- Vertin (Betahistine 8 mg) — for vestibular vertigo / Meniere’s
- Betavert Tab (Betahistine 24 mg) — full dose Meniere’s
Medical Disclaimer
This page is for educational purposes and does not replace personalised medical advice. Severe vertigo with hearing loss, neurological deficit, or fluctuating consciousness is not motion sickness — seek same-day medical assessment. Antihistamines and anticholinergics interact dangerously with alcohol and CNS depressants. Discuss any new medication with a qualified clinician, particularly during pregnancy, breastfeeding, or when taking other drugs.
More options in Travel Sickness Tablets
Ranked by recent MedsBase order volume — what other customers in this category are picking.
| Strength | 10 mg |
|---|---|
| Quantity | 30 Tablet/s, 60 Tablet/s, 90 Tablet/s, 180 Tablet/s |
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