Promethazine (Phenergan): What It Is and How It's Used for Motion Sickness
Educational summary · drug class: First-generation (sedating) antihistamine, phenothiazine derivative; antiemetic with anticholinergic and sedative effects · last reviewed 2026-06-29
Promethazine is a first-generation, sedating phenothiazine antihistamine used to help reduce the nausea, vomiting, and dizziness of motion sickness. The FDA label describes it as having anti-motion-sickness and antiemetic effects, and it commonly causes drowsiness. In the US it is prescription-only and carries a boxed warning against use in children under 2. The UK product Avomine is sold for motion sickness. Status varies by country.
Not medical advice. This page is for general educational and informational purposes only. It is not medical advice and is not a substitute for the advice of a qualified healthcare professional. Dizzout is not a medical provider — we are not doctors or pharmacists. The information here is a general summary drawn from sources such as the FDA-approved label and other public health resources, and it may not reflect the most current changes; the official product label is the authoritative source. Whether any medicine is right for you, and how much to take, are individual decisions that depend on your health, age, and other medicines. We do not provide dosing instructions — always read the product label and follow its directions. Talk to your doctor or pharmacist before starting, stopping, or changing any medication, and never disregard or delay professional medical advice because of something you read here. If you think you may have a medical emergency, contact a doctor or your local emergency number immediately.
What it is
Promethazine hydrochloride is a first-generation, sedating antihistamine — a phenothiazine derivative with H1-antagonist, antiemetic, anticholinergic, and sedative properties. Brands include Phenergan and, in the UK and EU, Avomine (promethazine teoclate) for motion sickness. In the US it is prescription-only. In the UK some promethazine products can be bought from a pharmacy as well as prescribed. Status differs by country and product, so check local rules.
Availability: Prescription-only (Rx) in the US; pharmacy and prescription in the UK (e.g., Avomine). Varies by country. Legal status, brand names, and availability vary by country — check what applies where you live.
How it may help with motion sickness
Motion sickness arises partly from conflicting signals between the inner-ear balance system, the eyes, and the brain. Promethazine blocks histamine H1 receptors and has anticholinergic activity in the brain's vomiting and balance pathways. Per the FDA/DailyMed label it has 'antihistaminic, sedative, antimotion-sickness, antiemetic, and anticholinergic effects,' which together reduce the nausea, vomiting, and dizziness of motion sickness.
General timing
The FDA/DailyMed label generally directs taking the first dose for motion sickness about 30 to 60 minutes before anticipated travel, with repeat doses later in the day as described in the label. UK NHS guidance similarly suggests taking it ahead of a journey, sometimes the night before. This is general label and guideline timing only. We do not provide dosing instructions — follow the product label or the advice of your doctor or pharmacist.
We don't provide dosing instructions. The exact amount, schedule, and whether it suits you are individual decisions — read the product label and follow its directions, and ask a doctor or pharmacist.
Common side effects
Sources such as the product label commonly list:
- Drowsiness or sleepiness (the most common effect)
- Dizziness
- Dry mouth
- Blurred vision
- Headache
- Confusion or disorientation
- Restlessness or, in some people, nightmares
- Constipation or difficulty urinating
Who should check with a doctor or pharmacist first
- Boxed warning: promethazine must not be used in children under 2 because of the risk of fatal respiratory depression; use caution in older children. Speak to a clinician before giving it to any child.
- Commonly causes drowsiness; do not drive, cycle, or use machinery if affected. The NHS notes drowsiness can persist and usually wears off within about 12 hours.
- Alcohol and other CNS depressants (sedatives, opioids) can add to sedation and respiratory depression.
- Older adults: may cause confusion and over-sedation; the label advises starting at lower doses.
- Pregnancy and breastfeeding: FDA Pregnancy Category C — discuss with a clinician.
- Contraindicated in comatose states and in people allergic to promethazine or other phenothiazines; use caution in asthma and other lower-respiratory conditions.
- May interact with MAO inhibitors, other anticholinergics, and many sedating medicines; check with a pharmacist or clinician about your other medicines.
- People with epilepsy, glaucoma, urinary or prostate problems, or liver or kidney issues should seek advice first.
Frequently asked questions
Is promethazine over the counter?+
In the US it is prescription-only. In the UK some promethazine products can be bought from a pharmacy as well as prescribed, and Avomine is sold for motion sickness. Status varies by country and product, so check locally.
Why can't promethazine be given to young children?+
The FDA label carries a boxed warning: promethazine must not be used in children under 2 because of the risk of fatal respiratory depression, and caution is advised in older children. Always talk to a clinician before giving it to a child.
Does promethazine make you sleepy?+
Yes — drowsiness is its most common effect, and it is a sedating antihistamine. The NHS notes drowsiness can persist and usually wears off within about 12 hours. Do not drive or operate machinery if affected, and avoid alcohol.
How soon before travel is promethazine taken?+
The FDA label generally describes a first dose about 30 to 60 minutes before travel, and the NHS notes it is sometimes taken the night before a long trip. We don't give dosing instructions — follow the label or ask your pharmacist.
Sources
Related
This page is for general educational and informational purposes only. It is not medical advice and is not a substitute for the advice of a qualified healthcare professional. Dizzout is not a medical provider — we are not doctors or pharmacists. The information here is a general summary drawn from sources such as the FDA-approved label and other public health resources, and it may not reflect the most current changes; the official product label is the authoritative source. Whether any medicine is right for you, and how much to take, are individual decisions that depend on your health, age, and other medicines. We do not provide dosing instructions — always read the product label and follow its directions. Talk to your doctor or pharmacist before starting, stopping, or changing any medication, and never disregard or delay professional medical advice because of something you read here. If you think you may have a medical emergency, contact a doctor or your local emergency number immediately.