Promethazine — NZ Medication Guide

📋 Reviewed by a Registered Pharmacist NZ — This information is for general educational purposes only and does not replace professional medical advice. Always consult your doctor or pharmacist before starting, stopping, or changing any medication.

What is Promethazine?

Promethazine is a first-generation phenothiazine antihistamine used for allergic conditions, nausea, vomiting, and insomnia. This medication is funded by Pharmac for nausea and allergic conditions.

What is Promethazine Used For?

Promethazine is used for motion sickness, nausea and vomiting (including hyperemesis gravidarum), allergic reactions and hay fever, pre-operative sedation, and short-term insomnia.

How Does Promethazine Work?

Promethazine blocks H1 histamine receptors (antihistamine effect) and muscarinic receptors (anticholinergic), as well as D2 dopamine receptors (antiemetic). Its strong sedative properties result from H1 blockade and CNS penetration.

How to Take Promethazine

For nausea/vomiting: 25 mg at bedtime or 12.5–25 mg every 4–8 hours. For motion sickness: 25 mg 1–2 hours before travel. For insomnia: 25 mg at bedtime. Available as tablets, elixir, and injection. Never inject subcutaneously (causes severe tissue necrosis).

Common Side Effects of Promethazine

• Sedation (significant — do not drive)
• Dry mouth
• Blurred vision
• Urinary retention
• Constipation
• Paradoxical excitation (in children)

Serious Side Effects — Seek Medical Attention

Contact your doctor or call 111 immediately if you experience any of the following:

• Respiratory depression (particularly in children under 2 — contraindicated in this age group)
• Neuroleptic malignant syndrome (rare)
• Extrapyramidal reactions
• Severe tissue necrosis (if subcutaneous injection occurs — IV only)
• QT prolongation

Drug Interactions

Promethazine may interact with other medicines. Always inform your doctor and pharmacist of all medications you are taking. Key interactions include:

• CNS depressants (significant additive sedation and respiratory depression)
• MAOIs (contraindicated)
• Anticholinergic medicines (additive effects)
• QT-prolonging medicines

New Zealand Prescribing Information

Promethazine hydrochloride (10 mg, 25 mg tablets; elixir; 25 mg/mL injection — Phenergan® and generics) is funded by Pharmac. Promethazine is CONTRAINDICATED in children under 2 years due to risk of respiratory depression and fatality. This warning was strengthened by Medsafe and international regulators. In older children (2–5 years), it should be used with caution and only on medical advice.

Frequently Asked Questions

Is promethazine safe for young children?

No — promethazine is contraindicated in children under 2 years due to the risk of potentially fatal respiratory depression. In children aged 2–5 years, it should be used with caution and only under direct medical supervision. For nausea in young children, safer alternatives should be used.

Can promethazine be used in pregnancy?

Promethazine is one of the more commonly used antiemetics for nausea and vomiting in pregnancy, including hyperemesis gravidarum, particularly when other measures have failed. It has been used for many decades in pregnancy with no clear evidence of fetal harm at standard doses, though all medicines should be used with caution in pregnancy.

References & Further Information

The following New Zealand and international resources were used to inform this page. We encourage you to consult these authoritative sources for the most current information:

• New Zealand Formulary — Promethazine
• Medsafe — Consumer Medicine Information
• Pharmac Funded Medicines Schedule

⚠️ Disclaimer: This page is for educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your doctor or a qualified health provider. In New Zealand, medication availability and funding may vary — check with Pharmac or your pharmacist for current information.

Reviewed by a Registered Pharmacist NZ