Medical Oncologist
Supportive medicines
Thyroid, epilepsy and psychiatric medicines
Thyroid tablets are usually straightforward. Epilepsy medicines are the group that matters most, because several substantially change how quickly the liver breaks down other drugs. Psychiatric medicines sit in between. All three categories are continued rather than stopped, because stopping carries its own serious risks.
NG
Medically reviewed by Dr. Naresh GunduConsultant Medical Oncologist · MBBS, DNB (Internal Medicine), DM (Medical Oncology, AIIMS) · last reviewed September 2026, next review due September 2027
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The short answer
Do thyroid, epilepsy and psychiatric medicines interact with chemotherapy?
Thyroid tablets are usually straightforward. Epilepsy medicines are the group that matters most, because several of them substantially change how quickly the liver breaks down other drugs. Psychiatric medicines sit in between, with some needing a real conversation and most continuing.
All three categories are continued rather than stopped. Stopping an epilepsy medicine risks seizures and stopping a psychiatric one risks a relapse, and both of those are far worse than any interaction being managed.
The epilepsy group is the one to raise first
Some older anti-epileptic medicines speed up liver enzymes so much that the amount of a chemotherapy drug reaching its target is meaningfully reduced. Your oncologist may want to discuss a switch with your neurologist before cycle one, and that takes time to arrange.
Mental health medicines are not optional extras
People leave antidepressants and anxiety medicines off the list out of embarrassment. They belong on it: several affect how other drugs are handled, and some interact with the anti-sickness medicines given on treatment day.
Bring the actual strips for all three categories. This is a group where the exact medicine, not the category, decides things.By group
What usually happens to each
- Thyroid tablets
- Almost always continued unchanged. The main practical question is timing, since they are taken on an empty stomach and treatment mornings disrupt that. Thyroid levels are sometimes rechecked during a long course.
- Older epilepsy medicines
- The group that most often prompts a change. Several speed up the liver enzymes that clear other drugs, which can reduce how much chemotherapy reaches its target. Your neurologist and oncologist should decide together whether a switch is worthwhile.
- Newer epilepsy medicines
- Generally less troublesome on this front, which is one reason a switch is sometimes suggested. Never make that change yourself; it has to be done gradually and under supervision.
- Antidepressants
- Usually continued. Some affect the enzymes that activate or clear particular drugs, and this genuinely matters for certain cancer treatments. Declare the exact medicine rather than the category.
- Anxiety and sleeping tablets
- Continued, with a caution: they add to the drowsiness caused by pre-medication and anti-sickness drugs. Tell the day-care nurse what you took on the morning of treatment.
- Medicines for serious mental illness
- Continued, and worth flagging early. Some affect the blood count or the heart's electrical pattern, both of which are already being watched during chemotherapy, so monitoring may be increased.
Not sure whether this applies to you?
Ask an oncologistPractical
What to do before cycle one
Four steps, and the first one is the only urgent one.
Raise the epilepsy medicines early
At the planning appointment rather than later, because if a switch is recommended it has to be made gradually. Ask whether yours is one of the medicines that affects drug clearance, and ask the question with the strip in hand.
Ask specifically
- Whether a switch is worth making
- How long a change would take
Get the specialists connected
Your neurologist or psychiatrist and your oncologist each need to know what the other is doing. Ask each for a letter for the other, and ask who is holding the whole picture.
Sort out the treatment-day timing
Thyroid tablets need an empty stomach; sedating medicines matter for whether you can get home safely. Ask for an instruction covering the morning of a cycle for each medicine.
Tell the nurse
- What you took that morning
- Anything sedating you are on
Never miss a dose because of a cycle
Vomiting after taking an epilepsy or psychiatric tablet needs a phone call, not a guess. Ask in advance what to do, because that is the situation most likely to arise and least likely to have been covered.
!
Get medical help the same day for these
A seizure, or more seizures than usual · vomiting that means an epilepsy or psychiatric tablet has not stayed down · unusual drowsiness or difficulty rousing someone · new confusion, agitation or hallucination · a racing or irregular heartbeat · muscle stiffness with a fever · thoughts of harming yourself or that life is not worth continuing. That last one needs someone told today, not at the next appointment. Say that the person is on chemotherapy and take the medicine list.
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Being straight with you
What this page cannot tell you
It cannot tell you whether your medicines interact. Within each of these categories the individual medicines behave very differently, and the answer depends on your chemotherapy drugs as well. This is a question for your oncologist or the hospital pharmacist with the actual strips in front of them.
It also cannot tell you whether a switch is worth making. That weighs a possible reduction in chemotherapy effect against the risk of destabilising seizure control or mental health, and only your two specialists can make that judgement together.
Nothing here is a reason to change anything
Do not stop, reduce or switch any of these medicines on your own reading. Withdrawal from an epilepsy or psychiatric medicine is dangerous in its own right, and is one of the few things on this whole subject that must never be attempted at home.
What to do next
Take the actual strips for all three categories to the planning appointment. Raise the epilepsy medicines first, since a switch takes time. Ask the pharmacist about your own combination. Get an instruction for treatment-day timing. And ask what to do if you vomit after a dose.
Commonly believed
Four beliefs that cause problems here
"I will pause my epilepsy tablets while on chemotherapy."
Stopping or reducing an anti-epileptic without supervision risks seizures, which is far more dangerous than any interaction being managed. If a change is needed it is made gradually by your neurologist, never at home.
"My antidepressant is a personal matter, not a medical one."
Several affect the enzymes that activate or clear particular cancer drugs, and some interact with anti-sickness medicines. Leaving it off the list out of embarrassment removes information that genuinely changes prescribing.
"Thyroid tablets are simple, so they need no mention."
They usually continue unchanged, and they still belong on the list. The practical question is timing on treatment mornings, since they are taken on an empty stomach, and thyroid levels are sometimes rechecked during a long course.
"A sleeping tablet on treatment morning is harmless."
Pre-medication and anti-sickness drugs are already sedating, and the combination leaves people far more drowsy and unsteady than they expect. Tell the day-care nurse what you have taken and arrange a lift home.
Questions we are asked
Common questions about these medicines
Why do epilepsy medicines matter so much?
Several of the older ones speed up the liver enzymes that break down other drugs, which can reduce how much chemotherapy reaches its target. Raise it at the planning appointment, because a switch takes time to make safely.
Will my epilepsy medicine be changed?
Sometimes it is suggested, and it is a judgement weighing chemotherapy effect against seizure control. Your neurologist and oncologist decide together. Never make the change yourself, as it has to be done gradually.
Can I keep taking my antidepressant?
Usually yes. Declare the exact medicine rather than the category, since some affect the enzymes that handle particular cancer drugs and some interact with anti-sickness medicines. Stopping abruptly is not the answer.
When should I take my thyroid tablet on treatment day?
Ask for a specific instruction, because it needs an empty stomach and treatment mornings disrupt that. It is usually manageable with a small adjustment to timing rather than skipping the dose.
What if I vomit after taking one of these tablets?
Call and ask whether to repeat it rather than guessing. For epilepsy medicines in particular a missed dose matters. Ask this question in advance so you already know the answer when it happens.
Do my thyroid levels need rechecking?
Sometimes during a long course, particularly if you become more tired than expected or your weight changes considerably. Ask whether it is part of your monitoring rather than assuming it is.
My mood has dropped badly since starting treatment. What should I do?
Tell your oncology team rather than waiting. Most units have a counsellor, adjustments can be made, and this is part of what they treat. If you are having thoughts of harming yourself, tell someone today.
Who is the best person to check my combination?
The hospital pharmacist, with your full medicine list in front of them. They are the most accessible source for this specific question and consistently the most underused.
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Sources
- Cancer Research UK — Cancer drugs and other medicines
- Macmillan Cancer Support — Other conditions and cancer treatment
- National Cancer Institute — Chemotherapy to Treat Cancer
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
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