Sodium Valproate (Epilim): Side Effects and Safety

Sodium valproate, commonly prescribed as Epilim (amongst other brand names), is one of the most effective anti-seizure medications (ASMs) for certain seizure types. It is also the ASM with the most significant safety requirements in the UK, particularly around pregnancy, and these have been updated recently. This guide explains the side effects and the current safety rules. It is general information and does not replace advice from a prescriber or epilepsy specialist.

What sodium valproate is used for

Sodium valproate is used for a broad range of seizures, including generalised tonic-clonic seizures, absence seizures and myoclonic seizures, as well as some focal seizures. For some generalised epilepsies it is the most effective option, which is why it is still prescribed within a careful framework of safeguards.

How sodium valproate works

Valproate increases the activity of a calming chemical messenger in the brain (GABA) and steadies electrical activity, reducing the likelihood of a seizure.

Common side effects

• Feeling sick, especially when starting treatment
• Tremor (shaking)
• Weight gain
• Temporary hair thinning or hair loss (hair often regrows, sometimes curlier)
• Drowsiness or dizziness

Taking the medication with food can ease nausea. Persistent effects are worth discussing with the prescriber.

Serious side effects to act on

Seek prompt medical advice for:

• Liver problems — unusual tiredness, repeated vomiting, abdominal pain or yellowing of the skin or eyes. This is rare, and the risk is higher in very young children and when more than one ASM is taken.
• Pancreatitis — sudden, severe stomach pain.
• Unexpected bruising or bleeding, which can indicate an effect on blood clotting.
• Confusion or marked drowsiness, which can occasionally signal a rise in ammonia levels.
• Thoughts of self-harm, which should always be raised without delay.

Pregnancy: the most important safety area

Sodium valproate carries the highest risk to a baby of any ASM when taken in pregnancy. The evidence shows:

• Around 1 in 10 babies may be born with a physical birth defect.
• Around 3 to 4 in 10 may experience neurodevelopmental problems, such as difficulties with learning and development.

Because of this, valproate must not be taken by anyone able to become pregnant unless the strict conditions of a Pregnancy Prevention Programme are met, and requires the Annual Risk Acknowledgement Form (ARAF) to be completed annually. This includes using highly effective contraception, a specialist review at least once a year, and signing a form confirming the risks are understood.

Anyone taking valproate who is planning a pregnancy, or who becomes pregnant, should contact their specialist urgently — but must not stop the medication on their own, because uncontrolled seizures are also dangerous.

The two-specialist rules (updated 2025)

The MHRA has tightened who can be started on valproate:

• New patients under 55. Anyone under 55 — female or male — being started on valproate for the first time needs two specialists to independently agree and document that no other treatment is suitable.
• Men already taking valproate. Following a change in February 2025, men under 55 who are already established on valproate can continue to be prescribed it by a single prescriber, without a second specialist review.

There is also a precautionary review of a possible, much lower risk (around 5 in 100 babies) of neurodevelopmental problems where fathers took valproate in the three months before conception. Men taking valproate should not stop on their own but can discuss any concerns with their specialist.

Do not stop suddenly

Stopping valproate abruptly can cause serious, prolonged seizures. Any change must be planned and supervised by the specialist team.

A note for carers and support staff

Staff supporting someone on sodium valproate should understand that it must never be stopped suddenly, should be able to recognise the serious side effects above, and should be aware of the pregnancy-related safeguards where they apply. This awareness supports, and does not replace, the person’s individual care plan and the decisions made with their specialist.

This article is general education and does not replace advice from a prescriber or epilepsy specialist. Never change or stop an ASM without medical advice.