Clozapine

You may experience some benefits in the first few weeks, but it could take several weeks before you start to feel any improvement.

Research has shown that about a third of people who start clozapine show an improvement in the first six weeks and this increases to two-thirds after one year.

Treatment with clozapine needs to start with a low dose that is gradually increased to a dose that is right for you over several weeks. The level of clozapine in your blood can be checked to see what dose is best for you.

Weight gain is a very common side effect of clozapine. It is more likely to cause weight gain compared with other antipsychotic medication. Young people naturally gain a little weight each year as they grow, but anything more than this should be monitored.

Your doctor will monitor your weight regularly when you’re taking clozapine. Talk to your doctor or pharmacist if you are concerned about your weight, or changes to your weight, while taking clozapine. They can review your medicine with you and look at any changes that could be made to help.

It’s very difficult to know how much weight you might gain, if any, as each person is affected differently. Reported weight gain tends to be more in the first year of treatment, especially the first few months.
Making sure you do enough exercise and eat a healthy diet (with vegetables and fibre) can help you to avoid putting on too much weight. Talk to your doctor, pharmacist and specialist healthcare team for advice on diet and lifestyle to help reduce the risk of weight gain.
Mental health conditions like schizophrenia and bipolar disorder can make being active and eating healthily more of a challenge. Talk to your doctor, pharmacist and specialist healthcare team for lifestyle advice and where to get support.

Clozapine can also affect how your body processes sugar, leading to high blood sugar levels. While this is uncommon, it can contribute to the development or worsening of diabetes, particularly in young people, and may be associated with weight gain.

Be alert for symptoms that suggest your body is struggling to process sugar, like excessive thirst, frequent urination, or persistent fatigue. If you experience these symptoms or have other concerns, schedule an appointment with your doctor.

If you already have diabetes, clozapine may impact your blood sugar levels. Discuss this with your doctor, monitor your blood glucose regularly, and you may need to adjust your diabetes medication accordingly.

Many people can produce more saliva than usual when they start to take clozapine, which can lead to drooling or dribbling. This usually happens early on in treatment and often gets better after the first few months, but can continue. If you’re affected, you should talk to your doctor or pharmacist about ways to manage it.

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.

Clozapine can make you feel very sleepy, especially when you first start taking it or when the dose is increased. This side effect can improve over time.

If it doesn’t, or if you are worried and it is causing you distress, speak to your doctor or pharmacist.

Depending on the dose you are prescribed, it may be possible to take your dose in the evening or at bedtime to help minimise the sedation you get.

If you need to take clozapine twice a day, taking a smaller dose in the morning may help.

If you have been taking clozapine for more than a month and you continue to feel very sleepy during the day, you should go back to your doctor and discuss what changes could be made to help.

Alcohol

It may be possible to drink some alcohol in moderation while taking clozapine. But the two together might make you feel very sleepy and unsteady on your feet, especially when you first start taking the medication.

It’s best to stop drinking alcohol completely during the first few weeks of treatment, until you see how the medication affects you.

Drinking alcohol every day, or in large amounts, can make your symptoms worse and may mean you won’t get the maximum benefit from your medication.

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.

Mixing clozapine and benzodiazepines (which may also be mixed in other street drugs) can be very dangerous. You may have difficulty breathing and your heart may stop working properly.
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.
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.

There are many other street drugs, but we don’t know what effect taking them with clozapine will have, so it’s best to be cautious. There is no regulation of street drugs or ‘legal highs’, so even if there are no known issues with the medication you take, the supply you receive might be mixed with other substances that could be dangerous.

Smoking

It is very important to tell your doctor or care team if you stop or start smoking while taking clozapine.

Smoking can have a huge effect on the level of clozapine in your body, and if you smoke it is likely that you will need a bigger dose of this medication.

If you stop smoking, or switch to vaping or nicotine replacement products, this is likely to significantly increase your clozapine levels and lead to increased side effects which could be very serious. It is important that you tell your doctor if you change your smoking habits or plan to give up. Your treatment will need to be reviewed and your dose reduced and monitored carefully.

Get more advice on drugs and alcohol.

Clozapine does not mix well with some other medicines, including herbal remedies. Some medicines may increase or decrease the metabolism of clozapine which could cause the level of clozapine to increase or reduce.
Combined hormonal contraceptives can increase the concentration of clozapine. Your doctor may need to review your dose if you start or stop this medicine.

Any medicines that can cause constipation should be used with care. This includes medicines like codeine for pain relief. Constipation can be a very serious side effect of clozapine.

The action of any medicine that causes sedation may be increased if combined with clozapine making you feel very tired and affecting your ability to do activities like driving a car or riding a bike safely.

Tell your doctor or pharmacist before you take clozapine if you are prescribed any other medication, to check that the combination is safe. This includes medicines you have bought at your pharmacy or local supermarket and medications that you put on your skin.

Look at the leaflet inside your medicine box for more information about other medicines that can interact with clozapine. With some medicines your doctor may need to adjust the dose of clozapine if you take them together. Ask a doctor or pharmacist for more information if you have any questions.

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.

Always let your pharmacist know if you have any food allergies or intolerances.

The tablets contain lactose so they may not be suitable for you if you have problems eating some sugars or dairy products.

The orodispersible tablets contain aspartame, which can be a problem for people with a condition called phenylketonuria.

There are multiple companies that manufacture clozapine, but you will usually be prescribed the same brand. If this does change, always check with the pharmacist if you are concerned about any of the ingredients in your medicine.

If you need to avoid animal products, please note that non-active ingredients used in the production of medicines may sometimes be of animal origin. Ask your pharmacist if you have any questions about the ingredients.

Further information about practical considerations for medicines if you need to avoid animal products can be found on the Vegan Society website.

You might feel sleepy or dizzy in the first few days or weeks after you start taking clozapine, or after an increase in dose.

It is recommended that you stop driving or riding a bike for the first few days or weeks after you start taking clozapine, until you know how it affects you.

Most people drive as normal while taking clozapine. If you are worried about this or have any concerns you would like to discuss, speak to your doctor or pharmacist.

You must tell The DVLA (Driver and Vehicle Licensing Agency) if you have bipolar disorder, schizophrenia, schizoaffective disorder or other mental health conditions that could affect your driving. You can be fined if you do not tell The DVLA about a medical condition that affects your driving and may be prosecuted if you are involved in an accident as a result.

Pregnancy

If you become pregnant while you are on clozapine, you should carry on taking it and make an appointment to see your doctor as soon as possible They can discuss the benefits and risks of continuing clozapine and help you to make a decision that is best for you and your baby. They may refer you to a specialist perinatal mental health team to support you with this decision.

If you are planning to get pregnant, it is recommended that you take folic acid while you are trying for a baby and during pregnancy. It is safe to take this together with clozapine.

Hormonal contraceptives may increase clozapine levels, so always discuss stopping these with your doctor so they can review your clozapine and adjust the dose if needed.

You can find out more information about taking clozapine during pregnancy at Bumps (Best Use of Medicines in Pregnancy).

Clozapine may slightly increase your chance of putting on extra weight and gestational (pregnancy-linked) diabetes during your pregnancy. Make sure your midwife is aware you are taking clozapine so they can advise on extra monitoring when appropriate.

During pregnancy it is standard practice for your midwife to assess your risk of blood clots. There are lots of things that can increase risk, and blood clots are also reported as a rare side effect of clozapine. If you have a higher risk of a blood clot, your doctor or midwife may advise the use of medicine to reduce this.

Remaining well is particularly important during pregnancy and while caring for a baby. If you have responded well to clozapine, continuing with this medicine in pregnancy may be the best option for you and your baby.

Post-natal

There are some symptoms that can occur in new born babies if clozapine is taken in the last three months of pregnancy. Look out for these and get help if they happen:

• jerking or twitching of the muscles or a tremor
• being jittery, irritable or constant crying
• being too hot or cold
• suckling/feeding difficulties
• having stiff or floppy muscles, or overactive reflexes
• being very sleepy or finding it difficult to sleep
• breathing problems

These are usually mild and go away in a few days without treatment.

Breastfeeding

Clozapine is passed to the baby through breast milk in small amounts and there is a risk that this might cause side effects in your baby. Your doctor or pharmacist can discuss the risks and benefits with you and consider other feeding options if appropriate.

If your baby was premature or has health problems, then you will need to be extra careful about taking medicines while breastfeeding. It may not always be best to breastfeed if this is the case, but you should discuss this with your doctor or midwife.

If your medication makes you sleepy, do not to sleep with your baby in the same bed, and be cautious when handling your baby (especially if waking during the night for feeds).

Talk to your doctor or midwife about your feeding options. Make sure that your doctor, nurse, or health visitor checks your baby for any side effects.

While other medicines might be preferred during breastfeeding, if you are taking clozapine this is probably because other medicines have not worked well for you, so switching to an alternative might not be right for you. It is important for you to remain well while you are bonding with and looking after your baby, so it may be best to take clozapine for your mental health when breastfeeding.

Sex

Clozapine is unlikely to cause side effects that affect your sex life and is also less likely to do so than other antipsychotic medications.

There have been incidents of retrograde ejaculation reported as a side effect in men taking clozapine. This means that no semen, or only a small amount, is produced when you ejaculate, and your urine may also be cloudy when you next go to the toilet. You should still experience the feeling of orgasm, but it could be a problem if you are planning a family.

Clozapine can, in rare cases, cause a long-lasting painful erection (priapism). If it lasts longer than three hours, go to A&E.
Clozapine might cause other side effects which might affect your sex life indirectly if you experience them, including:

• bedwetting
• producing more saliva and dribbling/drooling

If you do experience these side effects, and this is a problem for you, make an appointment to discuss this with your doctor.

Untreated illness can have a negative effect on your sex life, so if clozapine helps you to recover, positive effects can include improving your desire, experience and enjoyment of intimate relationships again.

Fertility

From limited studies available, there is currently no evidence to suggest that clozapine has any direct effect on fertility.

Other antipsychotics are more likely to cause an increase in prolactin (a natural hormone in the body). If this is raised it may cause problems with your menstrual cycle and you could miss periods (or they could become irregular or stop altogether). This means it may be more difficult to get pregnant.

If this has been a problem for you when taking other antipsychotic medicines, you should find that your periods will return to a regular pattern when you switch to clozapine, as this medicine does not cause an increase in prolactin levels.

There have been incidents of retrograde ejaculation reported as a side effect in men taking clozapine. This means that semen travels backwards into the bladder instead of out through the urethra (the tube that urine passes through). This means that no semen, or only a small amount is produced when you ejaculate. Your urine may also be cloudy when you next go to the toilet. You should still experience the feeling of orgasm, but it could be a problem if you are planning a family.

Talk to your doctor about your clozapine if you are trying to get pregnant or planning a family.

Clozapine is not a banned substance in sport.

Most people play sports as normal while taking clozapine. However, taking clozapine may make you feel tired and dizzy and affect your eyesight. This could be dangerous in some sports so it might be best not to take part in them for the first few days or weeks until you know how it affects you.

If you are worried that taking clozapine might make doing the sports you enjoy more difficult, discuss this with your doctor.

Ideally it is best not to take clozapine for the first time just before your exams. Clozapine could make you feel very tired and dizzy, make you feel restless and affect your eyesight.

You should talk to your doctor about any future exams if you are starting clozapine. You might decide together to delay starting it until you have completed them.

If they are more than a week away, however, you might find that it is better to start clozapine to improve your motivation and ability to study.
Most people take exams as normal while taking clozapine. If you are worried that taking clozapine might make studying for or taking your exams harder, discuss this with your doctor.