Topiramate (Topamax): Side Effects to Discuss With Your Prescriber

Topiramate, commonly prescribed by the brand name Topamax (amongst other brand names), is an anti-seizure medication (ASM) used to help control seizures and to prevent migraine. It can be very effective, but it has a distinctive side-effect profile and important safety measures around pregnancy that everyone taking it should understand. This guide is general information and is not a substitute for advice from a healthcare professional.

What topiramate is used for

Topiramate is prescribed for focal seizures and generalised seizures, sometimes on its own and sometimes alongside another ASM. It is also used to reduce the frequency of migraine attacks. As with other ASMs, it is introduced gradually.

How topiramate works

Topiramate has several actions in the brain that together reduce the excessive electrical activity underlying a seizure. Its broad range of effects also explains why it can cause side effects in areas such as thinking, appetite and body temperature.

Common side effects

• Tingling or “pins and needles” in the hands and feet
• Tiredness, drowsiness or dizziness
• Reduced appetite and weight loss
• Feeling sick and diarrhoea
• Changes in taste (fizzy drinks in particular may taste different)
• Difficulty concentrating, finding words or remembering things
• Changes in mood

The effects on concentration and word-finding are well recognised with topiramate. They are usually more noticeable when the dose is increased quickly, so any concerns are worth raising with the prescriber, who may adjust the pace.

Serious side effects to act on

Seek urgent medical advice for:

• Eye problems — sudden blurred vision or eye pain can, rarely, signal a rise in pressure within the eye (acute glaucoma), usually within the first month of treatment.
• Kidney stones — topiramate can increase the risk, so drinking plenty of fluid is sensible; severe pain in the side or back and blood in the urine should be checked.
• Reduced sweating and overheating — particularly in children and in hot weather.
• Persistent low mood or thoughts of self-harm — these should always be raised promptly.

Pregnancy: important safety measures

In June 2024 the MHRA introduced strengthened safety measures for topiramate because of the risks it poses in pregnancy. These measures matter for anyone who could become pregnant while taking it.

The evidence shows that topiramate taken in pregnancy is associated with:

• A higher risk of birth defects — around 4 to 9 in every 100 babies, compared with 1 to 3 in 100 in the general population.
• A higher chance of the baby being born smaller than expected — around 18 in 100, compared with about 5 in 100.
• An estimated two to three times greater risk of intellectual disability, autism spectrum disorder and attention deficit hyperactivity disorder.

Because of this, topiramate must not be used for migraine prevention during pregnancy, and it should only be used for epilepsy in pregnancy if there is no other suitable option.

The Pregnancy Prevention Programme

For girls and women who are able to become pregnant, topiramate is now prescribed only within a Pregnancy Prevention Programme. This means:

• Using highly effective contraception throughout treatment and for at least four weeks after the last dose
• A negative pregnancy test before starting
• A review by a specialist at least once a year
• Understanding and acknowledging the risks

Anyone in this group who is planning a pregnancy, or who becomes pregnant, should contact their specialist as soon as possible — but should not stop the medication on their own, because uncontrolled seizures also carry risks.

Contraception

At higher doses, topiramate can reduce the effectiveness of hormonal contraception. Anyone relying on the pill for contraception should discuss this with their prescriber so that a reliable method can be arranged.

Do not stop suddenly

Stopping topiramate abruptly can bring on seizures. Any change should be planned with the prescribing team.

A note for carers and support staff

Staff supporting someone on topiramate should be aware of the cognitive and appetite-related effects, the importance of good hydration, and the pregnancy-related safety measures where relevant. This complements the person’s individual care and support plan.

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.