Like all medicines, valproic acid can cause side effects, although not everyone gets them.
Common side effects of valproic acid
These common side effects of valproic acid may happen in more than 1 in 100 people. They're usually mild and go away by themselves. There are things you can do to help cope with them:
Stomach pain, feeling or being sick
This is most likely when you start treatment.
It usually helps if you take valproic acid with or after a meal or snack.
It may also help if you avoid rich or spicy food. Take small, frequent sips of water if you're being sick to avoid dehydration. Signs of dehydration include peeing less than usual or having dark strong-smelling pee.
If you take the combined contraceptive pill or progestogen-only pill and you're being sick, your contraception may not protect you from pregnancy. Check the pill packet for advice.
Diarrhoea
Drink plenty of fluids such as water or squash to avoid dehydration. Speak to a pharmacist if you have signs of dehydration, such as peeing less than usual or having dark, strong-smelling pee. Do not take any other medicines to treat diarrhoea without speaking to a pharmacist or doctor.
If you take the combined contraceptive pill or progestogen-only pill and you have severe, watery diarrhoea, or any diarrhoea that lasts for more than 24 hours, your contraception may not protect you from pregnancy. Check the pill packet for advice.
Dry or sore mouth, or swollen gums
For a dry mouth, try sugar-free gum or sweets, or sipping cold drinks. If this does not help, or you have mouth ulcers, talk to your pharmacist or doctor.
If you're bothered by swollen gums or this symptom does not go away, talk to your doctor or dentist.
Feeling tired or sleepy
As your body gets used to valproic acid, these side effects should wear off.
If these symptoms do not get better within a week or 2, your doctor may either reduce your dose or increase it more slowly. If that does not work, talk to your doctor as they may want to switch you to a different medicine.
Headaches
Make sure you rest and drink plenty of fluids. Do not drink too much alcohol.
Ask your pharmacist to recommend a painkiller. Talk to your doctor if your headaches do not go away or are severe.
Weight gain
If you find you're putting on weight after taking valproic acid, try to have a healthy balanced diet. Regular exercise will also help you keep your weight stable.
Your doctor will usually monitor your weight while you're taking this medicine. Speak to them if you have any concerns.
Thinning hair, or changes to the colour or texture of your hair
If these symptoms bother you, ask your doctor whether it's possible to lower your dose. Your hair may regrow after either reducing your dose or switching to a different medicine.
Irregular or delayed periods
As well as being a side effect of valproic acid, a late period is a sign that you could be pregnant, and valproic acid can be harmful for an unborn baby.
If you usually have regular periods, take a pregnancy test if your period is late, and speak to your doctor straight away if the result is positive.
Changes to your periods can also be a symptom of polycystic ovary syndrome (PCOS), a rare side effect of valproic acid. Your doctor will be able to do some tests to check whether you have PCOS.
Keep taking the medicine, but talk to your doctor or a 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's unusual to have serious side effects when taking valproic acid.
Call a doctor or call 111 straight away if you have:
- yellowing of the whites of your eyes, or your skin, although this may be less obvious on brown or black skin, and dark pee – these may be signs of liver problems
- severe nausea, vomiting or stomach pain – these may be signs of acute pancreatitis (an inflamed pancreas)
- unusual bruises or bleeding – these may be signs of a blood disorder
- shakes (tremors) in a part of your body, or unusual eye movements
Immediate action required: Call 999 or go to A&E if:
- you have thoughts about harming yourself or ending your life
Serious allergic reaction
In rare cases, valproic acid 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
Long-term treatment with valproic acid can cause osteoporosis and osteopenia (increasing your risk of breaking a bone).
Your doctor can arrange for tests to check the strength of your bones. Regular exercise and a good diet can also help to keep your bones strong.
Other side effects
These are not all the side effects of valproic acid. 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.