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Detailed medicine guidance

Side effects of sodium valproate

NHS medicines information on side effects of sodium valproate and what you can do to cope.

About this information

This NHS content is written for people in England. Medicine names, availability, prescribing and services may differ in other countries.

Common side effects of sodium valproate

These common side effects of sodium valproate 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

Take sodium valproate 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.

Talk to a doctor or pharmacist if these side effects get worse or do not go away.

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 diarrhoea 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 try 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 sodium valproate, 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. Try not to drink too much alcohol. Ask your pharmacist to recommend a painkiller. Talk to your doctor if your headaches are severe or do not go away.

Weight gain

If you find you're putting on weight after taking sodium valproate, 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 sodium valproate, a late period is a sign that you could be pregnant, and sodium valproate 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 polyendocrine metabolic ovarian syndrome (PMOS), a rare side effect of sodium valproate.

Your doctor will be able to do some tests to check whether you have PMOS.

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.

View the original NHS website page ↗. Refreshed 19 August 2026.

Licensed under the Open Government Licence v3.0 ↗. MyPHU is independent and is not endorsed by the NHS.

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