Olanzapine

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.

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.