Olanzapine | Atypical Antipsychotic Use & Side Effects

Medication name

Olanzapine ("oh-LAN-za-peen")
Brand name

Zyprexa® ("zi-PREX-a")
Medication type

Second-generation antipsychotic (sometimes referred to as an ‘atypical antipsychotic’)

Tablets: 2.5mg, 5mg, 7.5mg, 10mg, 15mg, and 20mg strengths

Orodispersible (‘melt in your mouth’) tablets: 5mg, 10mg, 15mg and 20mg strengths (these may be called Zyprexa Velotabs®)

Injections: 210mg, 300mg or 405mg in one injection (this may be called Zypadhera®)

This is a long acting intra-muscular injection that is administered every 2 to 4 weeks instead of taking tablets or liquid every day.

There is a short acting injection too. This would only ever be prescribed if you were in hospital, for short-term use only.

If you are 18 or over, the doctor can prescribe olanzapine for you as a licensed medicine for mania, schizophrenia and bipolar disorder.

If you are younger than 18 years old, a specialist doctor may still consider this as a treatment option.

A specialist may discuss this as an option to treat depression in combination with other antidepressant medication or to manage severe irritability, agitation or feelings of anger.

About olanzapine

Olanzapine is a second-generation antipsychotic (sometimes described as an ‘atypical antipsychotic’). It may also be described as a mood stabiliser.

There is a naturally occurring chemical messenger ('neurotransmitter') in the brain called dopamine, which is mainly involved in thinking, emotions, behaviour and perception.

With some illnesses, dopamine may be overactive, which upsets the normal balance of chemicals in the brain and can produce a variety of symptoms.

The main effect that olanzapine has is to block some dopamine receptors in the brain, correcting the overactivity of dopamine.

Olanzapine also has effects on other neurotransmitters in the brain such as serotonin. This can have positive effects, including reducing movement disorders and symptoms of depression and anxiety.

Olanzapine and everyday life

You should experience some benefits within the first one to two weeks of taking it, but it can take four to six weeks, sometimes longer, for olanzapine to show its full effects. This can vary between individuals and the reason why you are taking olanzapine.

You should stay in touch with your doctor to see how it goes over the first few weeks. They might do some tests to check your symptoms.

If you have had no good effects at all after two weeks, you should talk to your doctor about your progress. They may recommend increasing the dose or changing the medicine. Don’t increase your dose yourself if you think the medication isn’t working.

Your doctor might start you on a low dose and then increase it slowly over two to four weeks to your full dose.

If you are starting on the long-acting injection (Zypadhera®), it can take a few days for the first injection to start working.

If you switch from olanzapine tablets to the injection, you may need to continue taking your tablets for the first few weeks after your first injection, as the injection takes a few weeks to kick in.

A very common side effect of olanzapine is weight gain. One possible reason for this is because it increases appetite. It may also stop you from feeling full which makes it harder to know when to stop eating.

Olanzapine is more likely to cause weight gain compared with other antipsychotic medication.

Your doctor will monitor your weight regularly when you’re taking olanzapine.

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.

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 if this would be helpful.

If you do gain weight, most of this is likely to occur in the first six months of treatment. It is possible you may continue to gain weight after this time, but the rate of weight gain will usually be slower. This can happen even if you are taking a very low dose.

You may be more likely to gain weight if you have not taken this type of medication before, but it is not possible to predict how olanzapine will affect each person before they start taking it. Talk to your doctor or pharmacist if you are concerned about your weight, or changes to your weight, while taking olanzapine. They can review your medicine with you and look at any changes that could be made to help.

Olanzapine can also affect the way your body processes sugar. A side effect of olanzapine includes high blood sugar and, while not common, has been linked to the development of worsening of diabetes in some young people. This could also be linked to putting on weight.

It is important to watch out for symptoms that might mean your body is having trouble processing sugar. These include wanting to drink a lot, going for a wee a lot, feeling very hungry (even if you are eating lots), and feeling very weak or tired all the time. If you develop these symptoms, or any other symptoms you are concerned about, it is important to make an appointment with your doctor to discuss this.

If you already have diabetes, taking olanzapine may affect your blood sugar levels. Talk to your doctor and check your blood glucose levels regularly if this applies to you. You may have to increase the medication you use for your diabetes.

You may want to let your family and friends know you are taking olanzapine 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.

You may feel sleepy in the first few days of taking olanzapine. This should get better after the first week or two.

If the medicine makes you feel very sleepy, try taking it just before you go to bed.

If you have been taking olanzapine 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. This may include switching to a different medication.

Alcohol

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

During the first few weeks of treatment, it is recommended that you don’t drink alcohol until you know how the medicine affects you.

If you want to drink alcohol, it’s best to only drink small amounts, and have a plan for getting home safely if you go out.

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

Antipsychotics block the effect of dopamine, so the 'high' you get from drugs that work by increasing levels of dopamine may not be as 'high' as before. You may be tempted to increase your dose of the drug to make up for it, but this could be dangerous.

Cannabis can make drowsiness worse with olanzapine. It can also make your symptoms worse.

Cannabis and other drugs may have their own side effects on your mental health, like anxiety or psychosis.

Methadone can make drowsiness worse with olanzapine and potentially cause dangerous problems with the rhythm of your heart.

All antipsychotics can reduce the stimulant effects of cocaine.

There are many other street drugs, but we don’t know what effect taking them with olanzapine 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

If you start or stop smoking while you are taking olanzapine, you may have to change your dose.

Cigarette smoke affects the amount of olanzapine in your body.

If you smoke, you may need a higher dose of olanzapine than someone who does not smoke.

Tell your doctor if you smoke, so that you get the right dose for you.

If you stop smoking or switch to a nicotine replacement product or vaping, the level of olanzapine in the body rises, and you might need to reduce your dose of olanzapine slowly over one week. If you start or restart smoking, you may need to increase it again. Go to your doctor for advice if you stop or start smoking.

Get more advice on our drugs and alcohol guide.

Olanzapine does not mix well with some other medicines, including herbal remedies.

Tell your doctor before you take olanzapine if you are taking any other medicines, including things you have bought over the counter 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 olanzapine. With some medicines your doctor may need to adjust the dose of your medicines if you take them together. Ask a doctor or pharmacist for more information if you have any questions.

There are multiple companies that manufacture this medicine and the non-active ingredients may vary between products and also between the different strengths of tablets that are available.

Always let your pharmacist know if you have any food allergies or intolerances, and always check with them if you’re concerned about any of the ingredients in your medication.

The ordinary tablets may not be suitable for you if you have problems eating some sugars or dairy foods, as they contain lactose.

The orodispersible ('melt in your mouth') tablets may contain aspartame, which can be a problem for people who have a condition called phenylketonuria.

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.

Olanzapine may make you feel tired or dizzy when you start taking it.

This could affect you if you drive a car, ride a bike, or do anything else that needs a lot of focus.

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

Most people drive as normal while taking olanzapine. 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 olanzapine, 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 olanzapine 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.

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

Olanzapine can slightly increase your change of getting high-blood pressure in pregnancy (pre-eclampsia), gaining additional weight and gestational (pregnancy-linked) diabetes. Make sure your midwife knows you are taking olanzapine so they can monitor you.

Untreated mental illness can also be harmful to you and your developing baby, so decisions about stopping or avoiding medication when you are pregnant need to be discussed carefully with your doctor. If you and your doctor agree that it is best for you to continue taking olanzapine while pregnant, you should tell your midwife. 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 olanzapine.

Post-natal

Some newborn babies whose mothers take olanzapine during the last three months of pregnancy can get some symptoms at birth and soon after like restlessness, feeding difficulties or breathing problems.

Tell your midwife if you are taking olanzapine, so that they can help if the baby has any symptoms after birth.

Breastfeeding

Olanzapine is passed to the baby in breastmilk in small amounts. There is slight risk that the baby will become sleepier in breastfed when the mother is taking olanzapine.

If your baby was born early, then breastfeeding while you are taking olanzapine may not be recommended. Talk to your midwife and doctor about feeding options.

If you breastfeed while taking olanzapine, seek urgent medical advice if your baby becomes restless, very sleepy or develops feeding problems.

Sex

Olanzapine can have side effects that might affect your sex life. These include:

reducing your sex drive
difficulty getting an erection

Some other uncommon or rare side effects include breast growth or milk flow from the breasts (regardless of gender). These may affect your confidence and therefore your desire to have sex. Talk to your doctor if you get these symptoms.

In rare cases, olanzapine can cause a long-lasting and painful erection (called priapism). If this happens to you, you will need treatment from the hospital.

Fertility

Olanzapine may increase the level of a naturally occurring hormone called prolactin in the body although this is not a common problem for people who take olanzapine.

If you have raised prolactin levels (hyperprolactinaemia) this may affect your fertility, regardless of gender or sex.

For people who menstruate, raised prolactin levels may cause problems with your period and you might miss a cycle, they become irregular or they stop altogether. This can make it harder to get pregnant.

Talk to your doctor about your olanzapine if you are trying to get pregnant or planning a family and they can monitor your hormone levels.

Olanzapine is not a banned substance in sport.

Most people play sports as normal whilst taking olanzapine. However, it may affect your ability to play sports that require a lot of focus. It might be best to stop these sports for a few days until you know how it affects you or the effects get better.

If you have any concerns, discuss this with your doctor.

Ideally it is best not to take olanzapine for the first time just before your exams, as it may affect your memory or make you feel tried and dizzy.

It’s not possible to predict how the medication will make you feel, and if you do get any side effects, these are more likely to occur when you first start taking olanzapine.

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

If they are more than a month away, however, you might find that it is better to start olanzapine to improve your motivation and ability to study.

Most people take exams as normal while taking olanzapine, but if you have any concerns, discuss this with your doctor.

Information and safety considerations

Your doctor will consider any other medical conditions or symptoms you have before recommending a medicine for you.

Your medicine will come with a ‘patient information leaflet’. It’s important that you read this information. Speak to your pharmacist if:

you’re not given a leaflet
you don’t understand the information
you need it in a different format or language
you’re concerned about something you’ve read

The information leaflet also includes a list of warnings and precautions to consider before you take the medicine. If you think that any of these apply to you and are concerned that your doctor is not already aware of them, check with your doctor or pharmacist before you start to take your medication (or as soon as possible if you are already taking it).

Uses, warnings, safety and side effects

Taking olanzapine

Your doctor will advise you on how long it is best to keep taking your medication. This may vary depending on what you’re taking it for and how many times you’ve been unwell.

Many people take olanzapine for a few years.

For psychosis or schizophrenia, if you have had one episode of illness, then it is best for you to keep taking olanzapine for at least two years to reduce the chances of becoming ill again. If you have had more than one episode of illness, then a period of at least five years is recommended.

If you are taking olanzapine to treat bipolar mania or bipolar depression, then you will need to discuss long-term medicines for your bipolar disorder with your doctor. This is to help stop the illness coming back.

For bipolar disorder, it is important to remain on medicines in the long term because every time you become ill, there is more chance of you becoming ill again. Olanzapine can be used as a long-term medicine, but there are other choices too, and lithium is still thought to be the best long-term medicine for bipolar disorder. You should discuss your options with your doctor.

For schizoaffective disorder, it is probably best to keep taking the olanzapine for several years to reduce the chances of the illness coming back. We know less about schizoaffective disorder, but it has some similarities to bipolar disorder and some similarities to schizophrenia.

Depression is usually treated with an antidepressant medicine, and olanzapine is sometimes added to an antidepressant for more severe depression. For people with severe depression, it is best to continue the antidepressant medicine for at least two years to stop the illness from coming back. The doctor is likely to recommend continuing olanzapine for the same length of time. Your doctor should review your progress on this medication at least once a year.

You will get the best effect from olanzapine if you take it every day at the dose prescribed by your doctor.

You may start with a low dose that increases slowly to your regular dose over the next few days.

You will usually take your dose once a day.

It is usually recommended to take olanzapine at bedtime because it can cause sleepiness as a side effect. However, it is important to choose a time of day to take it that you can easily remember, which could be bedtime, a mealtime, or when you brush your teeth.

You can take it before or after food.

For the plain-coated tablets, swallow them whole with a drink of water – if you chew them, they taste bitter.

Put orodispersible tablets on your tongue and let them dissolve there. You can also dissolve these in a glass of water, orange juice, apple juice or milk and then drink it all down straight away.

If you receive your medicine by injection, a doctor or nurse will administer the olanzapine injection into a muscle in your bottom. This provides a long-lasting dose of olanzapine, lasting for two or four weeks. If you have just switched to the injection you may need to take tablets alongside this while the dose builds up. Every time you have the injection, you will be asked to wait at the centre for at least three hours. This is to check you do not have any unwanted reactions to the injection. The good thing about a long-acting injection is that you don’t have to remember to take so many tablets every day. It is slowly working in your body all the time between injections. The injection should switch between the left and the right side so that it’s not given in the same place all the time.

If you remember later during the day, take it as soon as possible.

If you forget to take it by your next dose, just take the next dose at the correct time. Do not try and catch up on missed doses by taking a double dose.

If it is less than 12 hours before your next dose of olanzapine, then do not take the missed dose because taking the doses too close together could cause more side effects.

If you miss your appointment for your injection, contact your doctor or nurse straight away to make another appointment.

It is very important to have the injection at the frequency prescribed for you, usually every two or four weeks.

If you forget to take your tablets for a while, or you miss an injection, you may start getting your old symptoms back or get withdrawal symptoms. You should talk to your doctor if this happens.

Regularly forgetting to take your medication can increase the risk of you becoming ill again and may mean that your symptoms could be worse if you become unwell again.

If you are struggling to remember to take your medication regularly as prescribed by your doctor, speak to your pharmacist and doctor for advice to help you.

Stopping olanzapine too soon after you have recovered may increase your risk of becoming unwell again. Discuss stopping your medication with your doctor. Planning and support are important to stopping olanzapine successfully.

Olanzapine is not addictive, but if stopped suddenly or the dose you are taking is reduced too much at once, you may experience withdrawal symptoms. These are caused by the receptors and levels of chemical transmitters in your brain readjusting after you reduce or stop your medication.

Some of the symptoms you get may be like symptoms you had when you were unwell, so understandably, you may feel anxious or upset that your illness could be returning.

Withdrawal symptoms usually start within a few days of stopping (or sometimes reducing) your medication. A wide range of symptoms have been reported. You may experience a few or a range of these:

difficulty getting to sleep or disturbed sleep
low mood, feeling anxious or agitated or restless
dizziness or light-headedness
headaches
reduced concentration or feeling confused
feeling sick or being sick, diarrhoea
flu-like symptoms
tense or jerky muscles and slow movements
uncontrollable movement of face or body
hallucinations, intrusive thoughts (you may experience these even if your medication wasn’t prescribed to treat psychosis)

It is not possible to predict if you will experience withdrawal symptoms (or how bad they will be if you do experience them). If you do experience symptoms, they are usually mild and don’t last long, but for some these could be severe enough to make you feel very unwell and last longer (two to three months or more), Arrange an appointment with your doctor to discuss your symptoms and seek advice if you are concerned or unable to tolerate them.

You can stop taking olanzapine safely with your doctor’s help. Planning a gradual withdrawal together can help to minimise or prevent the withdrawal symptoms you experience.

Warnings and safety

If you have taken more than the dose prescribed by your doctor, contact NHS 111 immediately to ask for advice, or ask a family member or friend to do this for you. This is important even if you don’t feel any different.

NHS 111 can give you advice and direct you to the best place to get more help if you need it.

If you have taken too much medication on purpose, or if after taking this you quickly feel unwell, call 999 or get someone to take you to A&E straight away. This includes any of the following signs:

rapid beating of the heart
agitation/aggressiveness
problems with speech
unusual movements (especially of the face or tongue)
reduced level of consciousness or coma
confusion
seizures or fits
a combination of fever, faster breathing, sweating, muscle stiffness and drowsiness or sleepiness, slower breathing, aspiration (breathing in vomit, mucus, or blood), high blood pressure or low blood pressure, and unusual rhythms of the heart
a painful erection (priapism) that lasts longer than three hours

If you need to go to A&E, do not travel alone or drive yourself there. Get your parent, family member or friend to go with you to support you and keep you safe on the way. If someone is not able to drive you there, call for an ambulance. Take your medication with you and tell doctors how much you have taken.

Serious side effects

Olanzapine can cause serious side effects, including allergic reactions.

Stop taking olanzapine and go to a hospital straight away if you get any of the following symptoms:

difficulty breathing
an allergic reaction or allergy (including symptoms such as swelling of your face, eyelids, lips, tongue or throat so that you cannot swallow or breathe, or really bad itching of the skin with raised lumps)
fever, muscle stiffness, sweating or drowsiness or sleepiness (these symptoms could be caused by neuroleptic malignant syndrome)

Get your parent, family member or friend to take you or go with you to support you and keep you safe on the way. If someone is not able to drive you there, call for an ambulance. Take your medication with you.

Contact your doctor immediately but don't stop taking olanzapine, if you get any of the following symptoms:

Increased pressure inside your eyes, which can damage your vision. This is a sign of glaucoma and symptoms include eye pain, red eyes, headache, tenderness around the eyes, blurred vision, and seeing rings around lights. An optician can check the pressure in your eye and advise you to go directly to hospital for urgent treatment if needed.
You may not be aware you have this. Make sure you go to an optician for an eye test every two years or every year if you are 15 or younger.
Swelling, pain, and redness in the leg, which may be from a blood clot. These clots could travel through blood vessels to the lungs causing chest pain and breathing difficulties.
Repetitive, regular movements of the tongue, mouth and face that you’re not able to control. This condition is called ‘tardive dyskinesia’ and is extremely rare but can be very serious. It may not stop even when you stop taking the medication. If you notice it early and act with your doctor, the problem should not get worse.
Tensing or contraction of muscles that you are not able to control. This could affect any muscle, including your eyes, mouth, tongue or jaw.
You develop new symptoms which include needing to drink a lot, needing to pee a lot, feeling weak or feeling hungry despite having an increased appetite. These might indicate your body is not processing sugar very well.

If you receive long-acting injections, this will be administered in a clinic so you can be observed for side effects of the injection for up to three hours afterwards. This is because of a risk of ‘post-injection syndrome’. This only occurs in about two per cent of people and in less than one in every 1000 injections given. If this does occur, symptoms include feeling very sleepy, dizziness, confusion, anxiety, irritability, difficulty walking and talking, and muscle stiffness or shaking. Symptoms usually stop within one to three days. If it is going to happen, it usually occurs within three hours of the injection, but if you get these symptoms later in the day, seek urgent medical help.

If you are unable to contact your doctor, call NHS 111 for urgent advice.

Side effects and your health

Side effects are more common when you first start taking olanzapine. Many go away as you continue your medicine. If they don’t get better, or if you are worried by them and they are causing you distress, speak to your doctor or pharmacist about them.

Very common side effects of olanzapine (affecting more than one in ten people) include:

feeling sleepy, tired, weak or exhausted
weight gain
increases in the levels of prolactin in the blood (may only be seen in blood tests)
feeling dizzy or faint with a slow heart rate, especially when getting up from a lying or sitting position (this usually happens at the start of your treatment and will normally pass on its own – speak to your doctor if it doesn't)

Common side effects of olanzapine (affecting up to one in ten people) include:

changes in the level of some blood cells, chemicals, circulating fats and, in early treatment, temporary increases in liver enzymes (seen only in blood tests)
increased appetite
tremor, muscle stiffness or unusual muscle movements
dry mouth
loss of strength or extreme tiredness
water retention leading to swelling of the hands, ankles or feet
joint pain
sexual problems such as feeling less like having sex less and problems getting an erection

Olanzapine use has been linked to an increased risk of developing diabetes among some young people. Symptoms include:

putting on weight
needing to wee a lot
needing to drink a lot
feeling weak
raised blood sugar levels

If you already have diabetes, you may need to increase the amount of medication you take for this alongside taking olanzapine.

There are other side effects that you can get when taking this medicine. We have only included the most common ones here.

This list of side effects can look scary. You may not experience any of them, but it’s important to be aware of them so you know what to do if they do happen.

Unless your side effects are very severe or distressing, try to continue taking your medication until you can talk to your doctor. Your doctor can make changes to your medication to help if needed.

You should have your weight, blood sugar, blood fats, prolactin level, blood pressure and pulse measured before you start olanzapine and regularly during early treatment, then at least every six months (if you are under 18) or once a year (if you are over 18) after that.

A blood test will be required to check your blood sugar, blood fats and prolactin level.

Your doctor might also check your heart with an electrocardiogram (ECG).

They might also check your height and development. If you have periods, they may ask if there have been any changes to the pattern or frequency of these.

It is very important to go for these checks when you are asked to do so. If you are worried or anxious about the monitoring, talk to your doctor, care team or practice nurse about this for advice and support.

You could take some of these measurements at home (e.g. weight) and keep a record of the results to share with your doctor when they review your treatment.