Phenergan

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Phenergan on Prescriptsy

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Phenergan is a brand name for promethazine hydrochloride, a first-generation sedating antihistamine used to treat allergic conditions, prevent and treat nausea and vomiting (including travel sickness), and as a short-term treatment for insomnia in adults.

Promethazine has been in clinical use since the 1940s and remains widely available in the UK as tablets (10 mg and 25 mg), oral solution (elixir), and injection.

Phenergan tablets and elixir are available from pharmacies without a prescription as pharmacy (P) medicines; the injection form is prescription-only (POM).

This page provides a detailed clinical guide to Phenergan, including how it works, dosage instructions, side effects, safety warnings, and how to obtain it in the United Kingdom.

Important safety information about Phenergan

Before reading further, please note these essential safety points.

• Phenergan must not be given to children under 2 years of age due to the risk of fatal respiratory depression.
• Phenergan causes drowsiness. Do not drive or operate machinery until you know how it affects you.
• Avoid alcohol while taking Phenergan, as it significantly enhances sedation.
• Use for insomnia should be short-term only (7 to 10 days maximum).
• Elderly patients are at increased risk of confusion, falls, and anticholinergic side effects.

Understanding allergic conditions and antihistamines

Allergic conditions such as hay fever (seasonal allergic rhinitis), perennial allergic rhinitis, urticaria (hives), and allergic conjunctivitis affect millions of people in the UK.

Allergies occur when the immune system overreacts to a normally harmless substance (an allergen), such as pollen, house dust mites, animal dander, or certain foods.

When an allergen is encountered, mast cells in the tissues release histamine and other inflammatory mediators.

Histamine acts on H1 receptors in the skin, nose, eyes, and airways, causing itching, sneezing, rhinorrhoea (runny nose), nasal congestion, urticaria, and watery eyes.

Antihistamines work by blocking H1 receptors, preventing histamine from exerting its effects.

First-generation antihistamines such as promethazine (Phenergan), chlorphenamine (Piriton), and hydroxyzine cross the blood-brain barrier readily and cause significant sedation.

Second-generation (non-sedating) antihistamines such as cetirizine, loratadine, and fexofenadine were developed to provide effective histamine blockade with minimal CNS penetration and therefore minimal drowsiness.

For most daytime allergy management, non-sedating antihistamines are preferred.

However, the sedating properties of promethazine can be useful in specific situations, such as when allergic symptoms are worst at night, when itch disrupts sleep, or for short-term insomnia.

How Phenergan works

Promethazine is a phenothiazine derivative with potent H1 antihistamine activity.

It competitively blocks histamine at H1 receptors throughout the body, reducing the vascular permeability, smooth muscle contraction, itching, and other allergic symptoms caused by histamine release.

In addition to H1 blockade, promethazine has several other pharmacological properties that explain its broad range of uses and its side-effect profile.

Its anticholinergic (antimuscarinic) activity produces a drying effect on secretions (reducing rhinorrhoea and watery eyes) and contributes to its antiemetic properties.

However, this same activity causes dry mouth, blurred vision, constipation, and urinary retention.

Its antidopaminergic activity at the chemoreceptor trigger zone in the brain contributes to its effectiveness against nausea and vomiting, including motion sickness.

This property also explains the rare extrapyramidal side effects (muscle stiffness, abnormal movements) seen particularly in children and at high doses.

Promethazine readily crosses the blood-brain barrier, which accounts for its marked sedative effect.

This property makes it effective as a short-term sleep aid but limits its usefulness for daytime allergy control.

After oral administration, effects begin within 20 minutes and last 4 to 12 hours depending on the dose and individual metabolism.

Clinical uses and UK guidance

Phenergan is licensed in the UK for the symptomatic treatment of allergic conditions of the upper respiratory tract and skin, including allergic rhinitis, urticaria, and allergic dermatoses; for the prevention and treatment of nausea and vomiting, including travel sickness; and as a short-term sedative for insomnia in adults.

NICE Clinical Knowledge Summaries (CKS) for allergic rhinitis recommend non-sedating antihistamines as first-line treatment for hay fever.

Sedating antihistamines such as promethazine may be used when symptoms are predominantly nocturnal or when sedation is desired (for example, to help with sleep disturbed by allergic itch).

For insomnia, NICE guideline NG215 recommends cognitive behavioural therapy for insomnia (CBT-I) as first-line treatment.

Short-term use of medication may be considered when non-pharmacological approaches have failed or are not available.

Promethazine is one option for short-term pharmacological treatment of insomnia, though the Z-drugs (zopiclone, zolpidem) and short-acting benzodiazepines are also used.

The BNF notes that sedating antihistamines are associated with next-day hangover effects and anticholinergic side effects and are best avoided for routine insomnia management.

For travel sickness, promethazine is effective when taken preventatively before a journey. Other options include hyoscine (Kwells), cyclizine, and cinnarizine. Promethazine has the advantage of long duration of action, making it suitable for long journeys.

Phenergan compared with other antihistamines

For daytime allergy management, non-sedating second-generation antihistamines are preferred.

Cetirizine (Piriteze), loratadine (Clarityn), and fexofenadine (Telfast) provide effective H1 blockade with minimal drowsiness and are suitable for long-term daily use.

Phenergan and other first-generation antihistamines (chlorphenamine, hydroxyzine) cause significant sedation and anticholinergic effects, limiting their suitability for daytime use.

Among the sedating antihistamines, Phenergan has the longest duration of action and the most pronounced sedative effect, making it particularly effective for night-time dosing.

Chlorphenamine (Piriton) has a shorter duration and slightly less sedation. Hydroxyzine (Atarax, Ucerax) is used primarily for anxiety-related itch and pruritus.

For nausea and travel sickness, cyclizine and cinnarizine are alternatives with different sedation profiles.

Dosage and administration

For allergic conditions in adults, take one 10 mg tablet twice daily or one 25 mg tablet at bedtime.

A single 25 mg dose at night is often sufficient for symptoms that are worst overnight (such as allergic rhinitis with nasal congestion or urticaria with night-time itch).

For children aged 6 to 10 years, the dose is typically 10 mg twice daily or 25 mg at night; for children aged 2 to 5 years, promethazine may be used at reduced doses under medical supervision.

Always use the dosing syringe or measuring cup provided for the oral solution.

For short-term insomnia in adults, take 25 mg (or up to 50 mg if needed) approximately 20 minutes before bedtime.

Use for no more than 7 to 10 nights. If insomnia persists, consult your GP for assessment and discussion of non-pharmacological approaches.

For travel sickness prevention, adults should take 25 mg the night before travel and a further 25 mg on the morning of the journey if needed.

For children aged 5 to 10 years, 12.5 mg the night before and on the morning of travel.

Take the dose at least 1 to 2 hours before the journey for maximum benefit.

Phenergan must not be given to children under 2 years of age. For all age groups, the lowest effective dose should be used for the shortest necessary duration.

Side effects of Phenergan

Drowsiness and cognitive effects

Drowsiness is the most prominent side effect and may persist for 12 hours or more after a dose.

Next-day hangover effects, including impaired concentration and slowed reaction times, are common, particularly at higher doses.

The DVLA advises that individuals taking sedating antihistamines should not drive if they are affected.

Even if you do not feel subjectively drowsy, your reaction times may be impaired.

Anticholinergic effects

Dry mouth, blurred vision, urinary retention, constipation, and difficulty concentrating are common anticholinergic side effects. These are more pronounced in elderly patients and those taking other anticholinergic medicines.

The cumulative anticholinergic burden may contribute to confusion, falls, and cognitive decline in older adults.

Paradoxical excitation

Some patients, particularly children and elderly adults, may experience paradoxical stimulation rather than sedation. This presents as restlessness, insomnia, agitation, irritability, or hyperactivity. If this occurs, stop Phenergan and consult your prescriber.

Rare and serious side effects

Blood dyscrasias (leucopenia, agranulocytosis), cholestatic jaundice, and extrapyramidal reactions (dystonia, akathisia, oculogyric crisis) are rare. Extrapyramidal reactions are more common in children and at high doses.

Photosensitivity (exaggerated sunburn) may occur. QT prolongation and cardiac arrhythmias are possible at very high doses or in overdose.

When to seek medical advice

Stop Phenergan and seek urgent medical advice if you develop severe drowsiness, difficulty breathing, signs of allergic reaction (swelling, rash, difficulty breathing), yellowing of the skin or eyes (jaundice), or involuntary muscle movements.

Call 999 in an emergency. Contact NHS 111 for persistent side effects or concerns.

Report suspected adverse reactions to the MHRA via the Yellow Card scheme at yellowcard.mhra.gov.uk .

Warnings and precautions

Age restrictions

Phenergan must not be used in children under 2 years of age due to the risk of fatal respiratory depression.

In children aged 2 to 5 years, it should only be used under medical supervision and for approved indications at appropriate doses.

The sedative and respiratory depressant effects of promethazine are of particular concern in young children.

Elderly patients

Older adults are more susceptible to anticholinergic side effects, including confusion, cognitive impairment, urinary retention, constipation, and falls. The STOPP/START criteria recommend avoiding first-generation antihistamines in elderly patients.

If Phenergan is used, the lowest dose should be given for the shortest time.

Alcohol and CNS depressants

Combining Phenergan with alcohol, benzodiazepines, opioids, or other sedating medicines can cause dangerous levels of sedation, respiratory depression, and loss of consciousness. Avoid alcohol completely while taking Phenergan. Inform your prescriber of all medicines you are taking.

Driving

Phenergan impairs driving ability. The DVLA advises against driving while affected by sedating medicines. The effects of promethazine may last 12 hours or more, so a dose taken at bedtime may still affect driving the following morning.

Conditions requiring caution

Use Phenergan with caution in patients with narrow-angle glaucoma, prostatic hypertrophy, urinary retention, epilepsy, severe cardiovascular disease, hepatic impairment, or pyloroduodenal obstruction. These conditions may be worsened by the anticholinergic effects of promethazine.

Pregnancy and breastfeeding

Promethazine has been used in pregnancy for nausea and is generally considered safe based on decades of clinical experience.

It is one of the antiemetics listed in the BNF for nausea and vomiting in pregnancy. Avoid use close to delivery due to the risk of neonatal sedation.

During breastfeeding, promethazine passes into breast milk in small amounts and may cause drowsiness in the infant. Use only on medical advice.

How to get Phenergan in the UK

Phenergan 10 mg and 25 mg tablets and Phenergan elixir are available without a prescription from pharmacies as P (pharmacy) medicines for adults and children aged 6 and over (check the specific product age recommendation).

The pharmacist will ask screening questions to ensure the product is suitable. Phenergan can also be prescribed by your GP on an NHS prescription.

The standard NHS prescription charge in England is 9.90 pounds per item; prescriptions are free in Scotland, Wales, and Northern Ireland.

Sources

• Phenergan 25 mg Tablets, Summary of Product Characteristics (EMC)
• Promethazine hydrochloride, British National Formulary (BNF)
• Promethazine, NHS
• NICE CKS: Allergic rhinitis
• NICE NG215: Insomnia
• MHRA Yellow Card Scheme