Like all medicines, baclofen can cause side effects in some people, but many people have no side effects or only minor ones.
Side effects often improve as your body gets used to the medicine.
Common side effects
These common side effects of baclofen happen in more than 1 in 100 people. There are things you can do to help cope with them:
Feeling sleepy, tired, dizzy or weak
If baclofen makes 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 tools or machinery if you feel dizzy. Do not drink any alcohol as it will make you feel more tired.
Feeling or being sick (nausea or vomiting)
Take baclofen tablets or liquid with or after a meal or snack. Stick to simple meals and do not eat rich or spicy food. If you're being sick, try small frequent sips of water to avoid dehydration. Signs of dehydration include peeing less than usual or having dark, strong-smelling pee.
If you take contraceptive pills and you're being sick your contraception may not protect you from pregnancy. Check the pill packet for advice.
Diarrhoea
Drink plenty of water or squash to prevent dehydration. Signs of dehydration include peeing less than usual or having dark, strong-smelling pee. If you get severe diarrhoea tell your doctor. Do not take any other medicines to treat diarrhoea without speaking to a pharmacist or doctor first. You may need to stop taking baclofen for a while until you feel better.
If you take contraceptive pills and have severe diarrhoea for more than 24 hours, your contraception may not protect you from pregnancy. Check the pill packet for advice.
Headaches
Make sure you rest and drink plenty of fluids. Do not drink too much alcohol. You can take an everyday painkiller like paracetamol. Talk to your doctor if they last longer than a week or are severe.
Problems sleeping
Avoid caffeine, alcohol, heavy meals and exercise for a few hours before going to bed. Relax before bedtime. Try taking a warm bath or listening to calming music.
Dry mouth
Chew sugar-free gum or suck sugar-free sweets
Rapid eye movements, blurred vision or difficulty focusing
These side effects should wear off after a few days as your body gets used to the medicine at that dose. If they last for more than a couple of days talk to your doctor as they may need to review your medicine.
Do not drive, ride a bike or use tools or machinery while you are having eye problems.
Excessive sweating or a mild rash
Try wearing loose clothing and using or a fan, where possible. If there is no improvement after a week, speak to your doctor.
It may help to take an antihistamine which you can buy from a pharmacy. Check with the pharmacist to see what type is suitable for you.
Increased need to pee or pain when you're peeing
These effects should wear off after a few days. If they last longer than that contact your doctor as they may need to review your medicine.
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
Serious side effects are rare and happen in less than 1 in 10,000 people.
Tell your doctor or call 111 if:
- the whites of your eyes turn yellow, or your skin turns yellow (this may be less obvious on brown or black skin) – this can be a sign of liver problems
- you have difficulty breathing while you're sleeping (sleep apnoea)
- you are having more muscle spasms than usual
Serious allergic reaction
In rare cases, baclofen 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.
Other side effects
These are not all the side effects of baclofen. For a full list see the leaflet inside your medicine packet.
You can report any suspected side effect using the Yellow Card safety scheme.