Side effects
Your medicine box contains a leaflet which describes all known side effects for your medication, both rare and common.
If you do get a side effect, please think about reporting it via the 'Yellow Card' scheme.
Some side effects of clozapine should get better after a few days of taking the medication. If they don’t, you should discuss them with your doctor. Expect early drowsiness and dizziness to settle as treatment goes on. This is why doses are built up slowly.
Do not suddenly stop taking your tablets until you have done this, as you may get ‘kick-back’ symptoms as well as losing the benefits of your treatment.
Body
Your weight could be affected by taking clozapine, although it’s very difficult to know how much weight you might gain, if any, as each person is affected differently.
Young people naturally gain a little weight each year as they grow, but anything more than this should be monitored.
Talk to your doctor if you are worried about gaining weight while taking this medication.
Up to one in ten people start to wet the bed when they begin taking clozapine. If this happens to you, restrict the amount that you drink before bedtime and speak to your doctor about other possible solutions, including medications that can stop bed-wetting.
Many people can produce more saliva than usual when they start to take clozapine, which can lead to drooling/dribbling. This usually happens early on in treatment and often gets better after the first few months. If you’re affected, you should talk to your doctor about ways to manage it.
Sex and fertility
Sex
Clozapine can have side effects that affect your sex life. These include:
- an erection that is painful and lasts for a long time (priapism). If you’re affected, you should see your doctor straight away as this can be dangerous.
- bed-wetting.
If any of these symptoms affect you, go back to the doctor and see what can be done.
Clozapine may have a good effect on your sex life as your symptoms settle, and you can concentrate on your relationships.
Fertility
There is nothing to suggest that clozapine has any effect on fertility, although not enough studies have been done to prove this.
If you have taken other antipsychotic medicines before clozapine, your periods may have been affected. People taking clozapine who have periods usually return to a regular period pattern.
Pregnancy, post-natal and breastfeeding
Pregnancy
You should tell your doctor if you are pregnant or trying for a baby before taking clozapine.
If you take clozapine while you are pregnant, it is not thought to have a bad effect on the developing baby.
Make sure you use a reliable method of contraception while you are taking clozapine if you do not wish to become pregnant. If you’re not sure what method to use, visit your doctor or make an appointment at a sexual health clinic to discuss your options.
Pregnant women are advised to take folic acid – this is safe to do while also taking clozapine.
You may also be checked for increased risk of blood clots during pregnancy and may be prescribed a course of blood-thinning injections.
Post-natal
Clozapine can cause symptoms in newborn babies if you take it during the last few months of pregnancy. These could include shaking, muscle stiffness and/or weakness, sleepiness, agitation, breathing problems and difficulty with feeding. Talk to your doctor or midwife about this and get their help and support.
Breastfeeding
Clozapine passes to the baby in breastmilk and can be harmful.
It can cause problems like excess sleepiness and low white blood cell count.
There is also a very small chance that your baby might have a seizure (fit).
For this reason, it’s best to discuss feeding options with your doctor or midwife.
Driving and transport
You might feel sleepy or dizzy in the first few days after taking clozapine. If this is the case, do not drive a car, ride a bike or operate machinery of any kind until you see how this affects you.
Don’t worry as most people who take clozapine are able to drive or ride a bike as normal after the first few weeks of treatment.
Friends and family
You may want to let your family and friends know you are taking clozapine so they can support you and help you look out for side effects.
For guidance on this, check out our page on getting support with your medication.
Sport
Clozapine is not a banned substance in sport
If you get a side effect like tiredness, dizziness or blurred eyesight, however, this might cause a problem for sports where you need a lot of focus. This is most likely to happen during the first few weeks of taking clozapine.
Try not to worry as most people are able to enjoy the sports they normally would while taking clozapine.
Alcohol and street drugs
Alcohol
You can drink alcohol while taking clozapine, but it could make you very sleepy and you could become unsteady and even take a fall. This will be most noticeable during the first few weeks of treatment.
It’s best to stop drinking alcohol completely during the first few days and weeks, until you see how the medication affects you.
Drinking too much alcohol (getting drunk) while taking clozapine can be very dangerous as it can affect your breathing.
Do not worry - most people are able to enjoy small amounts of alcohol while taking clozapine.
Street drugs
Clozapine does not mix well with street drugs as antipsychotics block the effect of dopamine, meaning that the ‘high’ you experience may not be as potent as before from any drug.
You may be tempted to increase your dose of the drug to make up for this, which could be very dangerous.
Smoking cannabis can make any drowsiness experienced when taking clozapine worse.
Cannabis and other drugs may have their own side effects on your mental health, like anxiety or psychosis. For more information, have a look at our drugs and alcohol page.
Clozapine is also likely to reduce the level of euphoria (happiness) you might normally experience when taking cocaine.
Clozapine and stimulant drugs such as amfetamines can affect the heart when taken together.
Prescription medicines
Tell your doctor or pharmacist if you are taking any other kind of medication as they may need to change your dose of clozapine or prescribe you a different medication.
Other medications can include tablets or liquids that you buy over the counter to treat common illnesses such as colds and flu, or topical medications that are applied to the skin.
Other interactions
Clozapine levels can be changed by high doses of caffeine.
If you drink a lot of coffee, cola drinks or other high-caffeine drinks, it may increase your level of clozapine and this might be dangerous.
If you suddenly stop drinking caffeine, it could make your clozapine level fall.
Talk to your doctor before making any major changes to your diet or what you drink regularly.
Monitoring
You will need regular blood tests all the time you are on clozapine. These blood tests check on the health of your white blood cells, which are important for fighting off infections.
Separate arrangements to check actual blood clozapine levels as a way of helping to get the dose right may be put in place but these tests are not strictly needed.
References and further reading
For more helpful links and information, have a look at our references and further reading page.