In short: Oxcarbazepine, sold in the UK under the brand name Trileptal and as generic versions, is an anti-seizure medication (ASM) used for focal seizures. Most early side effects are dose-related and often settle, but oxcarbazepine has one distinctive risk worth understanding: low blood sodium, known as hyponatraemia. Skin reactions also need prompt attention, particularly for anyone who has previously reacted to carbamazepine. No one should stop or change an ASM without medical advice.

What is oxcarbazepine and what is it used for?

Oxcarbazepine is an anti-seizure medication licensed in the UK for focal seizures, previously called partial seizures, with or without secondarily generalised tonic-clonic seizures. It can be used on its own or alongside other ASMs in adults and children aged six and over, according to the Trileptal Summary of Product Characteristics.

It is chemically related to carbamazepine and works by reducing excessive electrical activity in the brain, which lowers the likelihood of a seizure starting or spreading.

In NICE guideline NG217, oxcarbazepine is listed as a second-line monotherapy option for focal seizures and as a first-line add-on option. NICE also notes that oxcarbazepine may make seizures worse in people who have absence or myoclonic seizures, which is one reason prescribing decisions rest with an epilepsy specialist rather than being interchangeable across seizure types.

What are the common oxcarbazepine side effects?

Most side effects appear in the first weeks, relate to dose, and often ease as the body adjusts. They are typically neurological: drowsiness, headache, dizziness and double vision.

The frequency bands below come from the Trileptal SmPC, which uses the standard categories very common (more than 1 in 10 people), common (up to 1 in 10), uncommon (up to 1 in 100) and rare (up to 1 in 1,000).

Very common

• Drowsiness
• Headache
• Dizziness
• Double vision
• Nausea and vomiting
• Fatigue

Common

• Unsteadiness, tremor, involuntary eye movements
• Difficulty concentrating, memory problems, speech difficulties
• Blurred vision and vertigo
• Agitation, mood swings, low mood, confusion, apathy
• Diarrhoea, abdominal pain, constipation
• Rash, acne, hair thinning
• Weight gain
• Low blood sodium (hyponatraemia)

Longer-term use of oxcarbazepine has also been associated, rarely, with reduced bone density and fractures. This is relevant for people on ASMs for many years, and is covered further in our article on the link between epilepsy and osteoporosis.

As with all ASMs, there is a class warning about suicidal thoughts and behaviour. Any new or worsening low mood, hopelessness or thoughts of self-harm should be raised with a GP or epilepsy team promptly rather than waiting for the next review.

Oxcarbazepine and hyponatraemia: why sodium is monitored

Hyponatraemia means the level of sodium in the blood is lower than normal. It is the side effect most closely associated with oxcarbazepine, which is why blood tests are often arranged after starting or increasing the dose.

The SmPC reports that serum sodium below 125 mmol/l has been seen in up to 2.7% of people treated with oxcarbazepine, and that this is usually without symptoms and does not usually require a change of treatment. Where monitoring is advised, the recommendation is to check sodium after roughly two weeks, then monthly for the first three months, and afterwards as clinically indicated.

Who is more likely to be affected

Risk is higher in people taking medicines that also lower sodium, particularly diuretics (water tablets) and some antidepressants, and in older adults or anyone with reduced kidney function. Anyone in these groups should make sure their prescriber and pharmacist know about every medicine they take.

Symptoms to watch for

The patient information leaflet lists lethargy, confusion, muscle twitching and a significant worsening of seizures as possible signs of low sodium. Nausea, headache and unsteadiness may also feature, which can overlap with ordinary early side effects. This is why blood tests, rather than symptoms alone, are the reliable way to check.

Practical point for care staff: a person who becomes newly drowsy, muddled or notably more seizure-prone after a dose increase should be discussed with the prescribing team the same day, not logged and reviewed later. Recording baseline behaviour as part of good care planning makes changes far easier to spot.

What about skin reactions and hypersensitivity?

A mild rash is a common side effect, but any new rash on oxcarbazepine should be reported to a prescriber straight away rather than watched at home.

The SmPC is direct on this: anyone who develops a skin reaction should be promptly evaluated and oxcarbazepine withdrawn immediately unless the rash is clearly unrelated to the medicine. That decision is a clinical one.

Serious reactions are rare but recognised. These include DRESS (a drug reaction with fever, rash and internal organ involvement), and, very rarely, Stevens-Johnson syndrome and toxic epidermal necrolysis, which cause widespread blistering and peeling of skin and the linings of the mouth and eyes.

The carbamazepine link

This is the figure most often asked about. The SmPC states that people who have had a hypersensitivity reaction to carbamazepine should be told that approximately 25% to 30% of them may experience a hypersensitivity reaction with oxcarbazepine, including severe skin reactions. In other words, roughly a quarter to a third. Always tell your prescriber about any previous reaction to carbamazepine before starting oxcarbazepine.

The HLA-B*1502 genetic consideration

Carrying the HLA-B1502 gene variant is strongly associated with Stevens-Johnson syndrome and toxic epidermal necrolysis, and it is far more common in people of Han Chinese and Thai origin. Screening for this variant is recommended before starting treatment in these groups. A related variant, HLA-A3101, is associated with an increased risk of skin reactions in people of European and Japanese ancestry. If this may apply to you, ask your prescriber whether testing is appropriate.

Does oxcarbazepine interact with other medicines, including contraception?

Yes, and hormonal contraception is the interaction that most often gets missed.

Oxcarbazepine reduces blood levels of the hormones in combined oral contraceptives substantially, and the SmPC advises that additional or alternative non-hormonal contraception should be used. Do not assume a pill, patch or ring remains effective. Our guide to contraception and epilepsy explains how to have this conversation with a prescriber.

Oxcarbazepine can also interact with other ASMs, some blood pressure medicines, and medicines that lower sodium. Keep an up-to-date list of everything taken, including over-the-counter products, and check with a pharmacist before adding anything new.

On brands and generics, the MHRA places oxcarbazepine in Category 2 for switching between manufacturers’ products, meaning the need to stay on one manufacturer’s product should be based on clinical judgement and discussion with the person and their carer. We cover this in more detail in generic versus brand prescriptions.

What about pregnancy?

Decisions about ASMs in pregnancy must be specialist-led, and no one should stop taking their medicine on their own.

The MHRA’s safety review of anti-seizure medications in pregnancy examined oxcarbazepine alongside several other ASMs. Its central message to patients is unambiguous: do not stop taking the medicine without discussing it with your doctor, because uncontrolled seizures carry serious risks for both mother and baby.

Anyone taking oxcarbazepine who is pregnant or planning a pregnancy should ask for an urgent specialist review. Blood levels of oxcarbazepine’s active metabolite may fall during pregnancy, so monitoring may need to be adjusted.

When to seek urgent medical attention

Call 999 or go to your nearest emergency department immediately if you or the person you support has:

• Swelling of the lips, eyelids, face, tongue, mouth or throat, or sudden difficulty breathing. These are signs of a severe allergic reaction.
• A rash with blistering or peeling skin, or sores in the mouth, eyes or genitals, with or without fever.
• Fever with swollen glands and a rash.
• A seizure lasting five minutes or longer, or repeated seizures without recovery in between. See our guidance on status epilepticus and on when to call 999.
• Marked confusion, unusual drowsiness or unresponsiveness, particularly alongside a clear increase in seizures. This can indicate significant hyponatraemia and needs same-day assessment.

Contact your GP, epilepsy specialist nurse or NHS 111 the same day, without waiting for a routine appointment, for any new rash, yellowing of the skin or eyes, unexplained bruising or repeated infections, or a clear increase in seizure frequency.

Arrange a routine discussion with your prescriber for persistent drowsiness, dizziness, double vision, low mood, weight change or memory difficulties that are not settling.

What should you do about side effects?

Report them, and keep taking the medicine unless a healthcare professional tells you otherwise.

• Never stop or change an ASM without medical advice. Stopping abruptly can trigger seizures, including prolonged ones. Withdrawal, when appropriate, is done gradually under medical supervision.
• Keep a simple record. Note what happened, when, and how it relates to dose changes. This gives the prescriber something concrete to work with.
• Ask about timing and dose. Drowsiness and dizziness are often dose-related and may improve with a slower increase.
• Report suspected side effects through the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk.

Side effects are only one part of seizure control. Sleep loss, missed doses, illness and alcohol all matter too, as covered in our article on common and uncommon seizure triggers.

Frequently asked questions

Do oxcarbazepine side effects go away?
Many of the early effects, such as drowsiness, dizziness and nausea, ease over the first few weeks as the body adjusts, particularly when the dose is increased slowly. Anything persistent or troubling should be discussed with the prescriber rather than tolerated.

Is Trileptal the same as oxcarbazepine?
Yes. Trileptal is a brand name for oxcarbazepine. Generic versions contain the same active ingredient. Because oxcarbazepine is an MHRA Category 2 medicine, whether a person stays on one manufacturer’s product is a clinical decision made with them.

How often will my sodium be checked?
The SmPC recommends measuring serum sodium after around two weeks, then monthly for the first three months, and afterwards as clinically indicated. Your prescriber may test more often if you take diuretics or other medicines that lower sodium.

I had a rash on carbamazepine. Can I take oxcarbazepine?
Tell your prescriber before starting. Approximately 25% to 30% of people who reacted to carbamazepine also react to oxcarbazepine, so this needs to be weighed up by a clinician who knows your history.

Does oxcarbazepine stop the contraceptive pill working?
It can significantly reduce the effectiveness of hormonal contraception. The SmPC advises using an additional or alternative non-hormonal method. Speak to your GP, pharmacist or sexual health service before relying on hormonal contraception.

This article is general information about oxcarbazepine and is not a substitute for advice from a qualified healthcare professional. Always discuss your own medicines with your prescriber, epilepsy specialist nurse, GP or pharmacist.