HeadMeds gives young people in the United Kingdom general information about medication. HeadMeds does not give you medical advice. Please talk to your Doctor or anyone else who is supporting you about your own situation because everyone is different. Please read more important details about our site.

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Return to Olanzapine overview
  1. Use and Action
  2. Warnings and side effects
  3. Sex, drink, weight and everything else
Taking antidepressants  anti psychotic and mood stabilisers original listing
Taking anti-depressants, anti-psychotic and mood stabilisers
It feels like being really tired all the time...but it makes me feel less emotional

Please do not be worried by the side effects listed on this page. Some people take olanzapine without any side effects or only a few mild side effects. Some side effects wear off after a few days or weeks. If you think you might be getting a side effect from olanzapine, then you should discuss this with your doctor, nurse, or pharmacist.

Go to a doctor or hospital straight away if you get any of the following symptoms:

  • Allergic reactions (difficulty breathing, swelling of your face or throat, itching skin lumps).
  • Glaucoma (increased pressure inside your eyes, which can damage your vision – symptoms include eye pain, red eyes, headache, tenderness around the eyes, blurred vision, and seeing rings around lights).
  • Swelling, pain, and redness in the leg, which may be from a blood clot. Such a clot could travel through blood vessels to the lungs causing chest pain and difficulty in breathing.
  • Any combination of fever, faster breathing, sweating, muscle stiffness and drowsiness or sleepiness.
  • Another possible, but not very common, side-effect of olanzapine is repeating movements of the tongue, mouth and face. This is not an early side effect. It is more likely with older antipsychotics. 
  • This is called tardive dyskinesia.
  • The first sign might be some movements of your tongue that you cannot control, and they may be quite regular and rhythmic.
  • The problem with tardive dyskinesia is that it might not stop, even if you stop taking your medicine.
  • If you notice it early and take action with your doctor, the problem should not get worse.

Go and see your doctor straight away if the above happens.

Some side-effects that do appear should get better after a few days. If they do not, you should go back to your doctor.

Some side-effects of olanzapine may – strangely - seem like other mental health symptoms. Some side-effects here are also the opposites of each other. The balance of chemicals in the brain is very fragile, and hard to control! If they do not get better after a few days on the tablets, go back to the doctor.

Do not stop taking the tablets until you talk to your doctor, or you may get withdrawal symptoms as well.

Tell your doctor or pharmacist before you take olanzapine if you have any of these conditions.

You need to talk to your doctor or pharmacist if you have, or have a history of:

  • Stroke or “mini” stroke (temporary symptoms of stroke)
  • Parkinson’s disease
  • Prostate problems
  • A blocked intestine (‘paralytic ileus’)
  • Liver or kidney disease
  • Any blood disorders
  • Heart disease
  • Diabetes
  • Fits (Seizures, epilepsy)
  • Glaucoma
  • Respiratory (lung) diseases

Olanzapine does not mix well with some other medicines and drugs. 

Tell your doctor before you take olanzapine if you are taking any other medicines.

Always talk to the doctor if you are taking other medicines.

Tell the pharmacist you are taking olanzapine if you buy medicines (including things you put on your skin) for common illnesses.

Get your weight and blood checked regularly when you are taking olanzapine.

  • You will have your weight checked, and have some blood tests, when you start taking olanzapine.
  • You should then have your weight, blood sugar, blood fats, blood pressure and pulse measured regularly during early treatment, then at least 6 monthly or annually thereafter depending on your age.
  • You should also have your blood sugar tested when you start, after one month, and then every 4-6 months after that.
  • The doctor might also check your heart with an electrocardiogram ECG and check your blood pressure.
  • They might also check your height and development, and whether a young woman’s periods are regular.
  •  It is very important to go for these checks when you are asked to do so.

Olanzapine use has been linked to high blood sugar and diabetes in some young people.

  • Some studies have shown a risk of developing diabetes among young people who are taking olanzapine.
  • This could be linked to putting on weight.
  • Watch out for any early signs of diabetes:
  • wanting to drink a lot
  • going for a wee a lot
  • feeling weak
  • If you are a young person who already has diabetes, taking olanzapine may affect your blood sugar levels.
  • Talk to your doctor, and check your blood glucose levels regularly.
  • You may have to increase the medication you use for your diabetes.

Young people were more likely than adults to experience weight gain and to have changes in their blood fats, cholesterol and prolactin hormone while taking olanzapine.

Olanzapine does not mix well with drugs.

  • For drugs that produce a high by increasing levels of dopamine antipsychotics block the effect of dopamine, so this means the ‘high’ may not be as ‘high’ as before from any drug.
  • 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, and can also make your symptoms worse.
  • 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.

Stopping the medication causes the balance of chemicals in the brain to alter

Stopping this medicine quickly, or reducing the dose too much at once, may cause your old symptoms to come back, or cause you some withdrawal effects

You can stop taking it safely with your doctor’s help

  • Once you start taking an antipsychotic, the brain adjusts to having a new level of dopamine around.
  • If you stop taking the antipsychotic all at once, the balance starts to change again. You could get your old symptoms back.
  • People usually take olanzapine for a long time, to keep those symptoms away.
  • You may get your old symptoms back if you stop olanzapine for a while.
  • You can also get withdrawal effects including sweating, difficulty sleeping, shaking, anxiety, or feeling or being sick.
  • It is better to agree stopping with a doctor who will reduce you gradually.
  • This is likely to take a few weeks.
  • You will probably go for checks with your doctor after you stop olanzapine to check that you still feel better.

Reference sources

Search www.medicines.org.uk to find patient information leaflets and prescribing information on olanzapine. Plain tablets, orodisperible tablets and injection are listed separately and the original brand is Zyprexa but there are many other manufacturers. The SmPC lists all the inactive ingredients in the product so you can check against any allergies. If you are still unsure about this then speak to your pharmacist.

  • British National Formulary (BNF) and British National Formulary for children. Download the BNF/BNFC app (blue background) on to your mobile device. No longer available for public access via the web 
  • Taylor D, Barnes T, Young A. Maudsley Prescribing Guidelines in Psychiatry, 13th edition. Oxford: John Wiley & Sons, May 2018. ISBN: 978-1-119-44260-8
  • Royal Pharmaceutical Society. Medicines Ethics and Practice (42nd edition). London: RPS, 2018. Standards for pharmacists to work to. It is not a free publication
  • World Anti Doping Agency WADA Prohibited List https://www.wada-ama.org/en/resources/science-medicine/prohibited-list-documents 
  • Choiceandmedication; an independent source of information on many mental health conditions and their medicines with easy to read fact sheets www.choiceandmedication.org Personal subscriptions to download the app available for £1 per month (with proportionate discounts for longer periods) but your local mental health Trust may subscribe and provide information sheets for free.
  • Best Use of Medicines in Pregnancy (BUMPS). Information sheets on drugs in pregnancy http://www.medicinesinpregnancy.org/ 
  • Drugs and Lactation Database (LactMed). Information on drugs in breastfeeding https://toxnet.nlm.nih.gov/newtoxnet/lactmed.htm
  • NICE CG178 Psychosis and Schizophrenia in adults. Updated March 2014. Available online https://www.nice.org.uk/guidance/cg178
  • NICE CG155 Psychosis and schizophrenia in children and young people. Updated October 2016. Available online https://www.nice.org.uk/guidance/cg155
  • NICE CG185 Bipolar disorder: assessment and management. Updated April 2018. Available online  https://www.nice.org.uk/guidance/cg185

Some side-effects that do appear should get better after a few days. If they do not, you should go back to your doctor.

Don't stop taking Olanzapine until you talk to your doctor or you may get withdrawal symptoms as well.

Very common - could affect more than 1 in 10 people

  • weight gain
  • sleepiness
  • increases in levels of prolactin in the blood (seen only in blood tests)
  • In the early stages of treatment, some people may feel dizzy or faint (with a slow heart rate), especially when getting up from a lying or sitting position. This will usually pass on its own but if it does not, tell your doctor
  • Common - could affect up to 1 in 10 people

    • changes in the levels of some blood cells, chemicals, circulating fats and early in treatment, temporary increases in liver enzymes (seen only in blood tests)
    • increases in the level of sugars in the blood and urine (seen in tests)
    • feeling more hungry
    • dizziness
    • restlessness
    • tremor, muscle stiffness or unusual muscle movements
    • constipation
    • dry mouth
    • rash
    • loss of strength, or extreme tiredness
    • water retention leading to swelling of the hands, ankles or feet
    • fever
    • joint pain
    • sexual problems, such as feeling less like having sex for men and women, or problems getting an erection for men