Like all medicines, clonazepam can cause side effects in some people, but many people have no side effects or only minor ones.
Common side effects
These common side effects of clonazepam happen in more than 1 in 100 people. There are things you can do to help cope with them:
Disturbed sleep (such as vivid dreams)
Speak to a doctor. They may suggest a different medicine or a lower dose.
Feeling sleepy (drowsy) in the daytime
This should get better after about a week but speak to a doctor. They may suggest a lower dose. Do not drive, ride a bike or use machinery or tools until you feel better.
Feeling light-headed, unsteady or dizzy
If you feel dizzy when you stand up, try getting up very slowly or stay sitting down until you feel better. If you begin to feel dizzy, lie down so that you do not faint, then sit until you feel better.
Do not drive, ride a bike or use machinery or tools until you feel better.
If you still have these side effects after a week or they get worse, speak to a doctor.
Muscle weakness
Try to sit down if you feel weak. If you still have these side effects after about a week, or if they get worse, speak to a doctor.
Keep taking the medicine, but 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.
Serious side effects
It happens rarely, but some people can have serious side effects when taking clonazepam.
Call a doctor or call 111 now if:
- the whites of your eyes turn yellow, or your skin turns yellow although this may be less obvious on brown or black skin – this could be a sign of liver problems
- you see or hear things that are not there (hallucinations) or think things that are not true (delusions)
- you have problems with your coordination or controlling your movements
- you have swollen ankles, a racing heartbeat, a cough and feel tired – this could be a sign of heart problems
- you bruise easily, feel tired, have nosebleeds and have breathlessness – this could be a sign of blood problems
- you notice mood changes such as talking more than usual or feeling overexcited, restless, irritable or aggressive – these side effects are more likely in children or if you're over 65
Make an appointment to see your doctor if you have difficulty remembering things (amnesia).
Immediate action required: Call 999 or go to A&E now if:
- you have difficulty breathing or changes to your breathing
Do not drive to A&E. Ask someone to drive you or call 999 and ask for an ambulance.
Bring all the medicines you take with you.
Serious allergic reaction
In rare cases, clonazepam may cause a serious allergic reaction (anaphylaxis).
Immediate action required: Call 999 now if:
- your lips, mouth, throat or tongue suddenly become swollen
- you're breathing very fast or struggling to breathe (you may become very wheezy or feel like you're choking or gasping for air)
- your throat feels tight or you're struggling to swallow
- your skin, tongue or lips turn blue, grey or pale (if you have black or brown skin, this may be easier to see on the palms of your hands or soles of your feet)
- you suddenly become very confused, drowsy or dizzy
- someone faints and cannot be woken up
- a child is limp, floppy or not responding like they normally do (their head may fall to the side, backwards or forwards, or they may find it difficult to lift their head or focus on your face)
You or the person who's unwell may also have a rash that's swollen, raised, itchy, blistered or peeling.
These can be signs of a serious allergic reaction and may need immediate treatment in hospital.
Do not drive yourself to A&E.
The person you speak to at 999 will give you advice about what to do.
Long-term side effects
Clonazepam can cause withdrawal symptoms if you take it for a long time.
If you're prescribed clonazepam for more than 4 weeks, your dose may be reduced gradually when you stop taking it to prevent withdrawal symptoms.
Other side effects
These are not all the side effects of clonazepam. For a full list, see the leaflet inside your medicine packet.
Reporting side effects
You can report any suspected side effect using the Yellow Card safety scheme.
Visit the Yellow Card website for more information about reporting side effects.