This NHS content is written for people in England. Medicine names, availability, prescribing and services may differ in other countries.
Common side effects of promethazine
There are things you can do to help cope with these side effects of promethazine:
Feeling tired during the daytime
Drowsiness usually wears off within 12 hours of taking a dose. Do not drive, cycle or use tools or machinery if you're feeling this way.
Nightmares
Speak to your pharmacist or doctor if nightmares do not go away or are troubling you.
Feeling dizzy or unsteady on your feet, or having difficulty concentrating
Stop what you're doing and sit or lie down until you feel better. If the feeling does not go away or is troubling you, do not take any more promethazine and speak to a pharmacist or doctor.
Headaches
Make sure you rest and drink plenty of fluids. Ask your pharmacist to recommend a painkiller. Talk to your doctor if the headaches last longer than a week or are severe.
Speak to a doctor or pharmacist if the advice on how to cope does not help and a side effect is still bothering you or does not go away.
View the original NHS website page ↗. Refreshed 19 August 2026.
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