This NHS content is written for people in England. Medicine names, availability, prescribing and services may differ in other countries.
Common side effects of chlorphenamine
These common side effects of chlorphenamine happen in more than 1 in 100 people. There are things you can do to help cope with them:
Feeling sleepy during the daytime
Drowsiness usually wears off 4 to 6 hours after a dose. Do not drive, ride a bike or use tools or machinery if you're feeling this way.
Feeling sick (nausea)
Try taking your tablets with food. It may also help if you do not eat rich or spicy food while you're taking chlorphenamine.
Feeling dizzy or 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 chlorphenamine and speak to a pharmacist or your doctor.
Do not drive or ride a bike if you're feeling dizzy or unable to concentrate.
Dry mouth
Chew sugar-free gum or suck sugar-free sweets.
Headaches
Make sure you rest and drink plenty of fluids. Ask your pharmacist to recommend a painkiller.
Talk to your doctor if the headaches do not go away or are severe.
Blurred vision
Do not drive, ride a bike or use tools or machinery while this is happening.
This is usually only a mild problem but if it bothers you, speak to your pharmacist or doctor as you may need to change your treatment.
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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