How fast does zyprexa work?

(updated 2/2019)


Don’t dismiss this medication too fast. You’ll hear this medication described as an antipsychotic as well as a “mood stabilizer”. (What’s an antipsychotic?) But within weeks of its release by the FDA as an antipsychotic, psychiatrists were figuring out that it had fast mood stabilizing properties. Since then the manufacturer has obtained FDA approval for marketing olanzapine as a mood stabilizer. This means that a doctor could offer you an “antipsychotic” when you don’t have “psychosis” at all. Instead, she could be offering it to you simply because it’s a very fast, often extremely effective medication for the symptoms of bipolar disorder (it even may help antidepressants work in people who don’t clearly have bipolar disorderMarangell).

This medication can be unbelievably effective, with remarkably few side effects. But brace yourself, and don’t stop reading until the end of this little essay because there may be some good news in sight. However, you need to know that in routine doses (10-20mg) it can cause a lot of weight gain. There is a case report of a 58% body mass increaseBryden, and a recent thorough review ranked olanzapine just behind clozapine in the weight gain championships, at 10 lbs in 10 weeks!Wirshing Twenty-five pounds in a year is not uncommon. Thus the big risk from this medication, the main limiting factor (beside it’s phenomenal cost) to it’s use in bipolar disorder, is this risk of weight gain.

In addition, there is now plenty of evidence that this medication can cause diabetes in some people. Gianfrancesco, Caro, Hedenmalm Usually, but not always, that’s because of the weight gain it can cause. The FDA requested that Eli Lilly put a warning about this on their package insert. A 2004 Consensus Statement from the American Diabetes Association, along with the American Psychiatric Association, includes specific warnings about diabetes.

But it’s really good for some problems

Nevertheless, you should be aware of olanzapine for symptoms that simply must be controlled now. It can decrease anxiety, agitation, even the overall negative feeling called “dysphoria” — within 20 to 30 minutes. It has a profoundly calming effect in many people. It can stop “racing thoughts” that can be one of the most severe symptoms of bipolar disorder, especially in Bipolar II — as well as the more obvious symptoms of paranoia or delusions as seen in Bipolar I. Sometimes tiny doses are enough to help a lot, and these doses do not seem to so commonly lead to weight gain (2.5mg is the smallest pill; sometimes even half of that is quite useful in bipolar II).

Because it can treat both mood symptoms and psychotic symptoms, it has a role also in people where the diagnosis is not clear. The doctor does not have to be certain whether you have bipolar disorder or schizophrenia or even depression with psychotic features”: all will respond. It is like a broad-spectrum antibiotic” that doctors can use before they are certain just which bacteria you have. Later more specific medications can be used.

Why switch , if olanzapine works well right away? Fair question. The risk of weight gain and possibly even getting diabetes is the main reason to consider switching (if you’re paying for the medication yourself, that’s the other reason — it’s so expensive, you may not want to buy more than a few pills). The risk of weight gain is higher if you’re thin; people who are already overweight are less likely to see big gains from olanzapine.

Antidotes to olanzapine-induced weight gain

Finally, you should know that research is continuing on the use of medications to block this weight gain, or even reverse it. This is such an important topic I made a page on Weight Gain and Bipolar Treatment to discuss it.

Cigarettes and Smoking/Vaping

A mother wrote to describe her son’s experience on olanzapine: it only really worked when the dose was very large. Ah, it came to light: he’d been smoking/vaping at school, a lot. Using tobacco products causes the liver to make enzymes that increase the breakdown of olanzapine. To get the same amount in the bloodstream requires nearly double the oral dose when patients are smoking or vaping.

This does not happen with nicotine replacement, oral or patch. Only with tobacco smoke. As best I can tell (after 15 minutes of surfing around Pub Med), chewed or inhaled tobacco does not interact with olanzapine.

This means that it could take a high dose of olanzapine to get a routine amount of the medication in the bloodstream of a smoker/vaper. And, if someone stops smoking/vaping, their olanzapine dose may need to be lowered, a lot. Those “coulds” and “mays” are necessary because all this interacts with the person’s usual rate of metabolizing olanzapine, which can range from very fast to very slow. So the impact of smoking/vaping can be large or small).

(Fancy genetic tests now available can identify whether a person is a slow or rapid metabolizer — for $300+, which someone pays even if it’s not the patient/family. If not them, it may well be us, funding Medicare. I think there are better ways our Medicare dollars could be spent. That’s because another way to find out about a person’s metabolism is just to carefully adjust the dose upward until it works, and downward until any side effects are manageable or gone — the way we all did it before the fancy tests. Old school…)


Side effects

Please do not be worried by the side effects listed on this page. Some people take olanzapine without any side effects or with 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.
Do not stop taking the tablets until you talk to your doctor, or you may get withdrawal symptoms as well.

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

  • weight gain
  • increases in the levels of prolactin in the blood (seen only 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. If not, tell your doctor
  • 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.


A common side effect of olanzapine is weight gain. You need to have your weight checked regularly while you are taking it.

Talk to your doctor about this if it worries you.

It is thought that one of the reasons olanzapine causes weight gain is that it increases appetite.

Making sure to do enough exercise and eat a healthy diet (with vegetables and fibre) can help you to avoid putting on too much weight.

Sex and fertility


Olanzapine can have side effects that might affect your sex life, but they should not last for long. These include:

  • drop in libido (how much you want to have sex)
  • difficulty getting an erection
  • (very occasionally) breast growth and, in very rare instances, some milk flow, regardless of gender

Some of these effects should pass after the first couple of weeks. If they do not, and this is a problem for you, go back to the doctor and see what other medicines you could try.

The good effects of olanzapine may have a positive impact on your sex life as your symptoms settle, and you can concentrate on your relationships.


Olanzapine may increase the level of a hormone called prolactin in the body for a short time when you start taking it, but not to a very high level. If prolactin levels do rise for a short time after starting olanzapine, this may affect fertility, regardless of gender. However, this is not a common problem for people who take olanzapine.

If you are trying for a baby, or become pregnant while taking olanzapine, you should speak to your doctor as soon as possible.

Pregnancy, post-natal and breastfeeding


Olanzapine is not seen as high-risk during pregnancy and, if regular medicine is keeping you well, then changing your medication may be the greater risk. A study of over 800 mums who took olanzapine during pregnancy suggested no increased risk of malformations, miscarriage or premature birth.

Olanzapine is an antipsychotic medicine. Taking antipsychotics can cause folate levels to become low, which is not good for a healthy pregnancy. Taking 5mg folic acid a day before and during pregnancy can reduce the risk of your baby having spine problems.

Olanzapine may slightly increase your chance of getting high blood pressure linked to pregnancy (pre-eclampsia), putting on extra weight and gestational (pregnancy-linked) diabetes.

Expect your blood sugar levels, weight and blood pressure to be more closely checked from month four onwards of your pregnancy if you are on olanzapine.
A blood-thinning agent may also be advised. This is because sometimes there can be a risk of getting a blood clot in the leg during pregnancy.


Taking olanzapine close to delivery may lead to some discontinuation (withdrawal) effects in your baby. These may include being irritable, crying or problems feeding and sleeping. These are usually mild and go away in a few days without treatment.

Make sure that your doctor, nurse, or health visitor checks your baby for any side effects. These can include:

  • being extra sleepy
  • having colic
  • feeding problems
  • being floppy
  • poor weight gain


Olanzapine gets into breast milk, but only in small amounts (around 1%).

Breastfeeding may help with any discontinuation (withdrawal) effects.

There is a risk of the baby becoming a little sleepier if breastfed when the mother is taking olanzapine.

You should talk to the doctor if you are taking olanzapine and thinking of breastfeeding after you give birth to your baby.

If your baby was premature or has health problems, then you will need to be extra careful about taking medicines while breastfeeding. Discuss this with your doctor.

Remember that it is important for you to stay well while you are bonding with and looking after your baby. This means that you may need to take olanzapine or another medicine for your mental health when breastfeeding.

Talk to your doctor or midwife about your feeding options.

Driving and transport

Do not drive a car or ride a bike just after you start taking olanzapine.

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 might be best to stop doing these things for the first few days, until you know how it affects you.

Do not worry – most people drive as normal while taking olanzapine.

School and exams

Try not to take olanzapine for the first time just before your exams.

Olanzapine can make you feel tired and dizzy, and can affect your memory.

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.

You might find that it is better, however, to start olanzapine to improve your symptoms and your ability to study and do the exams.

You could take your olanzapine at night (if you do not do that already) to see if that is better for you.

Do not worry – most people take exams as normal while taking olanzapine.

Friends and family

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.


Olanzapine is not a banned substance in sport.

It can, however, make you feel tired or dizzy, so this might affect your performance in sports that need a lot of focus.

You need to see how it affects you.

Do not worry – most people play sports as normal while taking olanzapine.

Alcohol, street drugs and smoking


You can continue to drink some alcohol while taking olanzapine, but having the two together might make you very sleepy or make you fall over.

If you drink a lot of alcohol, these effects will be much more serious.

Alcohol can also make the symptoms of your condition worse.

During the first few days, it might be best to stop drinking alcohol until you see how the medicine affects you.

If you want to drink alcohol, remember that you might be sleepy and make sure you can get home safely.

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. For more information, have a look at our drugs and alcohol page.

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.


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, the level of olanzapine in the body rises, and you might need to reduce your dose of olanzapine slowly over one week.

If you (re)start smoking, you may need to increase it again

Go to your doctor for advice if you stop or start smoking.

Prescription medicines

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.

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


You should have your weight, blood sugar, blood fats, blood pressure and pulse measured regularly during early treatment, then at least every six months to a year after that, depending on your age.

You should also have your blood sugar tested when you start, after one month, and then every four to six 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. If you have periods, they may also check whether they are regular.

It is very important to go for these checks when you are asked to do so.

References and further reading

For more helpful links and information, have a look at our references and further reading page.

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