Side effects and interactions of ASMs

As with all medications, anti-seizure medication (ASM) can cause side effects and possible side effects vary from one ASM to another. Whether you will have side effects or not depends on how you react to the drug (as people can respond differently to the same drug). How important side effects are depends on how important they are to you.

Information about side effects is included in the patient information leaflet (PIL) that comes with the packaging for each medication. The list of side effects can be long and off-putting. But listed side effects are only possible side effects. They do not always happen.

They are often listed by how frequently they occur, such as ‘common’ and ‘rare’. These terms are the same for all drugs and they show how likely it is that a side effect will happen (how many people will have it). Knowing what these terms mean may help to put side effects into perspective, and help you to make decisions about taking medication or not.

The possible side effects of ASM may affect the choice of ASM. For example, medication that causes extreme sleepiness might be avoided for a student who needs to be alert in class. There are also particular issues around ASM for women and girls who are, or may become, pregnant (see below). 

If you are having side effects that are causing you concern you can talk to your specialist, Epilepsy Specialist Nurse (ESN), or GP.

Types of side effects

• Allergic reactions are rare and usually happen very quickly after starting an ASM. An itchy skin rash is often the first sign of an allergic reaction. If you have an allergic reaction, it is important that you speak to your specialist, a GP, or pharmacist as soon as possible about what to do. Allergic reactions can be very serious.
• Dose-related side effects happen when the dose of a drug is too high, and usually go away if the dose is reduced. This is why medication is usually started at a low dose and increased slowly.    
• Long term (or chronic) side effects happen when a drug is taken for a long time, usually many years.

Side effects can be difficult to recognise in babies, children, and people with learning disabilities as they may not be able to say how they are feeling. If your child is taking ASM and feels unwell, you might notice a change in their behaviour. 

If you have a side effect which isn’t listed in the PIL, you can report this to the Medicines and Healthcare Products Regulatory Agency (MHRA), the agency responsible for the safety of medicines in the UK, via their yellow card scheme.

What are drug interactions? 

Some drugs can affect, and be affected by, other drugs. This is called a ‘drug interaction’. When two drugs interact, how one or both drugs work will be affected. Interactions can result in one or both drugs:

• working better (being more effective); or
• working less well, for example, if one prevents the other from working or speeds up how quickly it is eliminated (got rid of) from the body, so it has less time to work.

Drug interactions can happen between different ASMs, and between ASM and other types of drugs including non-prescription (or ‘over the counter’) medications, complementary therapies, and herbal remedies. For this reason, it is helpful to say if you are taking other drugs before starting ASM, or that you are taking ASM before starting any other drugs. 

Usually, there is no interaction between ASM and frequently used pain relief medications such as those containing paracetamol or ibuprofen.

ASM and alcohol

Alcohol can affect how well ASM works and can also trigger seizures for some people. This depends on the ASM, how much the person drinks, and how they react to alcohol. Drinking alcohol when taking ASM is a personal choice and the PIL, or your specialist, will be able to tell you more about drinking alcohol with that medication.

When should I take my ASM?

ASM works best when it is taken regularly and at about the same time every day. For most ASMs it does not matter when in the day you take them, only that you try to stick to the same time each day. If you take it more than once a day it is useful to try to take it evenly spread out. 

It is important to take ASM regularly because this helps to keep the levels in your body ‘topped up’, to stop seizures from happening. If you are unsure about when to take your ASM you could talk to your specialist or pharmacist. 

The aim of taking ASM is to make your treatment as simple and convenient as possible so that it fits into your daily routine.

How long will I have to take ASM for? 

How long you need to take ASM for depends on your epilepsy, your seizures, and how you respond to the ASM. Most people will take ASM for at least several years and sometimes for life. 

For some people, seizures stop or go away on their own (called spontaneous remission). In this case, they might come off their medication with help from their neurologist (with medical supervision). 

Some children have an epilepsy syndrome where their seizures stop at a particular age and so they may be able to stop taking their ASM at that point.

Are all ASMs the same? 

Most ASMs have two names: a generic name (for example carbamazepine) and a brand or trade name given by the manufacturer (for example Tegretol). The generic name refers to the active ingredient in the drug (which works to control, or treat, the condition it is taken for). 

Some ASMs have more than one generic form, each of which has the same active ingredient, and each can be given its own name. For some ASMs different forms may use different ingredients, such as binding or colouring agents, which can affect how they are absorbed and used in the body. 

Swapping between different forms of ASM could affect seizure control or cause side effects. So it is often recommended that, once you have found a form of ASM to control your seizures, you take the same form of this ASM all the time (with every prescription) whether it is generic or branded. This is called ‘consistency of supply’. 

It is a good idea to check that you have the right form of ASM before leaving the pharmacy as they may not be able to change it once you have left.

Some drugs are made abroad and brought into the UK. Other drugs are made in the UK, exported, and brought back to the UK. These are called ‘parallel imports’. They are sometimes labelled in a different language or have different packaging from usual. If you are concerned about your medication, you can ask your doctor to write ‘no parallel imports’ on your prescription.

My child has epilepsy - will ASM affect their behaviour or learning? 

The aim of medication is to stop seizures without side effects or impact on behaviour. However, some children may have side effects that affect their behaviour, although these may go away after a few weeks. Some changes in behaviour could be due to the seizures themselves or other things, such as how the child feels about their epilepsy and how other people react, or they may just be a part of growing up. 

Many people find that their epilepsy and medication does not impact on their learning. However, for other children it might have an effect, for example, due to seizures disrupting their lessons or medication affecting their concentration. If you are concerned about whether ASM is affecting your child, you can talk to their paediatrician.

Are there any special issues for girls and women? 

Some ASM can affect periods and some types of contraception, and some types of contraception are less effective for girls and women taking particular ASMs. This depends on the individual, which ASM they take, and the type of contraception they use. 

Some girls and women have catamenial epilepsy - where their seizures happen at a particular time during their menstrual cycle. They may be prescribed an extra ASM, alongside their regular ASM, to take when seizures are likely to happen.

ASM and birth defects 

Taking ASM while pregnant may affect a developing baby. However, these risks need to be carefully considered for each person and balanced against the possibility of seizures happening during pregnancy which may also affect a developing baby, or the safety of the mother. 

Different ASMs vary in the risk they pose, and the risk of birth defects rises with higher doses of the drug. Taking more than one ASM also increases the risk. Sodium Valproate (including Epilim, Depakote, Episenta, Epival, Kentlim, Syonell, Valpal, Belvo, Convulex, Dyzantil and Orlept), and Topiramate (Topamax) have greater risks in pregnancy than other ASMs. The MHRA has issued guidance and information on the risks of taking Sodium Valproate and Topiramate during pregnancy. 

If you are thinking of starting a family, it is essential that you talk to your neurologist about planning your epilepsy treatment for pregnancy, and for when the baby arrives.

Epilepsy Society is grateful to Dr F J Rugg-Gunn, Consultant Neurologist & Honorary Associate Professor Clinical Lead, Chalfont Centre for Epilepsy, who reviewed this information.

Information updated: July 2024