Olanzapine is a generic drug prescribed to adults and certain children with schizophrenia and bipolar I disorder. As with other drugs, olanzapine can cause side effects, such as weight gain and high blood sugar.

Olanzapine is available as the brand-name drug Zyprexa.

Olanzapine comes as an oral tablet. Olanzapine also comes in other oral forms and forms that are injectable, but this article does not cover them.

Read on to learn about potential common, mild, and serious side effects of olanzapine. For a general overview, including details about its uses, see this article on olanzapine.

Olanzapine has a boxed warning. A boxed warning is the most serious warning from the Food and Drug Administration (FDA). For details, see the “Olanzapine: Side effect specifics” section.

Olanzapine can cause certain side effects, some of which are more common than others. These side effects may be temporary, lasting a few days to weeks. However, if the side effects last longer than that, bother you, or become severe, be sure to talk with your doctor or pharmacist.

These are just a few of the more common side effects reported by people who took olanzapine oral tablet in clinical trials. These side effects can vary depending on which condition the drug is being used to treat. More common side effects can also vary between children and adults. (Olanzapine oral tablet is approved for use in children ages 13 to 17 years.)

When taking olanzapine for schizophrenia

More common side effects in adults taking olanzapine for schizophrenia include:

More common side effects in children taking olanzapine for schizophrenia include:

  • drowsiness
  • headache
  • dizziness
  • increased appetite
  • weight gain*

* For more information about this side effect, see “Olanzapine: Side effect specifics.”

When taking olanzapine for bipolar I disorder

More common side effects in adults taking olanzapine for bipolar I disorder include:

More common side effects in children taking olanzapine for bipolar I disorder include:

  • drowsiness
  • headache
  • fatigue
  • increased appetite
  • weight gain*

* For more information about this side effect, see “Olanzapine: Side effect specifics.”

Mild side effects can occur with olanzapine use. This list doesn’t include all possible mild side effects of the drug. For more information, you can refer to the prescribing information for olanzapine oral tablets.

Mild side effects that have been reported with olanzapine include:

These side effects may be temporary, lasting a few days to weeks. However, if the side effects last longer than that, bother you, or become severe, be sure to talk with your doctor or pharmacist.

Note: After the FDA approves a drug, it tracks and reviews side effects of the medication. If you develop a side effect while taking olanzapine and want to tell the FDA about it, visit MedWatch.

Olanzapine oral tablet may cause serious side effects. The list below may not include all possible serious side effects of the drug. For more information, you can refer to olanzapine’s prescribing information.

If you develop serious side effects while taking olanzapine, call your doctor right away. If the side effects seem life threatening or you think you’re having a medical emergency, immediately call 911 or your local emergency number.

Serious side effects that have been reported and their symptoms include:

* For more information about this side effect, see “Olanzapine: Side effect specifics.”
† Olanzapine has a boxed warning for this side effect. A boxed warning is the most serious warning from the FDA. For more information about this side effect, see the “Olanzapine: Side effect specifics” section.

Help is out there

If you or someone you know is in crisis and considering suicide or self-harm, please seek support:

  • Call or text the 988 Lifeline at 988 or chat at 988lifeline.org. Caring counselors are available to listen and provide free and confidential support 24/7.
  • Text HOME to the Crisis Text Line at 741741 to connect with a volunteer crisis counselor for free and confidential support 24/7.
  • Not in the United States? Find a helpline in your country with Befrienders Worldwide.
  • Call 911 or your local emergency services number if you feel safe to do so.

If you’re calling on behalf of someone else, stay with them until help arrives. You may remove weapons or substances that can cause harm if you can do so safely.

If you’re not in the same household, stay on the phone with them until help arrives.

Allergic reaction

For some people, the olanzapine oral tablet can cause an allergic reaction.

In general, symptoms of allergic reaction can be mild or serious.

Ways to manage

For mild allergic reaction symptoms, such as a mild rash, call your doctor right away. They may recommend treatments to help manage your symptoms. They’ll also let you know whether you should keep taking the medication.

For severe allergic reaction symptoms, such as swelling or trouble breathing, call 911 or your local emergency number right away. These symptoms require immediate medical care because they can become life threatening. If you’ve had a serious allergic reaction to an olanzapine oral tablet, your doctor may recommend taking a different medication instead.

The olanzapine oral tablet may cause several side effects. Here are some frequently asked questions about the drug’s side effects and their answers.

What happens if a “normal person” takes olanzapine?

In a person who doesn’t have a mental health condition olanzapine is approved to treat, the drug may cause drowsiness, weight gain, or changes in mood. Olanzapine is approved to treat conditions including schizophrenia and bipolar I disorder.

Olanzapine belongs to a class of drugs called atypical antipsychotics. The exact way the drug works isn’t clear. Olanzapine may work by affecting the level of certain neurotransmitters (chemical messengers) in the brain, including dopamine and serotonin. These substances affect mood and behavior, among other body functions.

Olanzapine can cause mild and serious side effects. These may be the same or different in a person who doesn’t have a mental health condition the drug is used to treat. The drug also has several precautions, including a boxed warning — the most serious warning the FDA issues. For details, see the “Olanzapine: Side effect specifics” section.

For more information about olanzapine side effects, talk with your doctor.

Can olanzapine cause long-term side effects?

Yes, it’s possible. Long-term side effects have been reported in people taking olanzapine. “Long-term side effects” can refer to side effects that begin after you’ve taken a medication for a long time or to side effects that may continue even after you stop taking the medication.

Long-term side effects reported with olanzapine include:

Talk with your doctor or pharmacist if you have questions about olanzapine and long-term side effects. You should let them know if you have side effect symptoms that don’t go away after a few days. They can review your symptoms and determine the best treatment, which may include stopping olanzapine.

Are olanzapine side effects in females different compared with males?

No, olanzapine side effects don’t differ in females and males.* However, certain olanzapine side effects can cause different symptoms in females and males.

Treatment with olanzapine can cause high prolactin levels (hyperprolactinemia), which was rarely reported in the drug’s studies. Some hyperprolactinemia symptoms, such as loss of interest in sex, can happen in females or males.

But other symptoms can differ in males versus females. For example, females may experience vaginal dryness and irregular periods. Hyperprolactinemia can also cause reversible effects on fertility (the ability to become pregnant) in females. Symptoms in males can include erectile dysfunction and headache.

Talk with your doctor if you have questions about olanzapine treatment and possible symptoms of hyperprolactinemia to watch for.

* Sex and gender exist on spectrums. Use of the terms “male” and “female” in this article refers to sex assigned at birth.

Does olanzapine 5 mg cause different side effects than other strengths?

No, the 5-milligram (mg) strength of oIanzapine is not reported to cause different side effects compared with other strengths. However, your risk of certain side effects can vary based on your dose. In studies, certain side effects were more common with higher olanzapine dosages. You may hear these referred to as dose-dependent side effects.

Dose-dependent side effects of olanzapine include:

  • dizziness
  • drowsiness
  • dry mouth
  • fatigue
  • high prolactin levels
  • weight gain (see “Olanzapine: Side effect specifics”)

Talk with your doctor or pharmacist if you have additional questions about your olanzapine dose, including how it affects the side effects you may experience.

Learn more about some of the side effects that olanzapine may cause. To find out how often side effects occurred in clinical trials, see the prescribing information for olanzapine oral tablet.

Increased risk of death in older adults with dementia-related psychosis

Similar to other antipsychotic medications, olanzapine has a boxed warning about the increased risk of death in older adults (ages 65 years and older) with dementia-related psychosis. A boxed warning is the most serious warning from the FDA.

Olanzapine and other antipsychotic medications should not be used to treat dementia-related psychosis. In older adults, this use has increased the risk of death in studies of atypical antipsychotics. These are also called second-generation antipsychotics, the drug class olanzapine belongs to.

Dementia is a term used for symptoms that affect your memory, thinking, and ability to communicate. It’s caused by conditions such as Alzheimer’s disease and Lewy body dementia, a condition that can occur with Parkinson’s disease.

Psychosis refers to changes in a person’s perception that causes a loss of touch with reality. Symptoms of psychosis include hallucinations and delusions. Psychosis is a possible behavioral disturbance in people with dementia. Antipsychotic medications such as olanzapine are prescribed to treat psychosis due to certain causes, but aren’t approved to treat dementia-related psychosis.

What you can do

Due to this risk, doctors do not prescribe olanzapine or other antipsychotics to treat psychosis related to dementia. They’ll prescribe a safer treatment for this condition instead.

Weight gain

Weight gain is a common side effect reported in studies of olanzapine. Weight gain due to olanzapine may be mild or serious. It may be accompanied by other metabolic changes olanzapine can cause, such as high cholesterol and type 2 diabetes. Weight gain and metabolic changes are known side effects across atypical antipsychotics.

In studies, weight gain continued through long-term treatment with olanzapine. For example, some people gained 25% or more of their body weight after 48 weeks of olanzapine treatment.

Weight gain caused by olanzapine appears to be dose-dependent. This means higher doses are more likely than lower doses to cause this side effect. Children who take olanzapine have a higher risk of weight gain compared with adults. But this side effect can affect people of any age taking olanzapine.

What you can do

If you’re prescribed olanzapine, your doctor will monitor your weight and other signs of changes to your metabolic health (such as your blood sugar level) throughout treatment. Talk with your doctor if you have concerns about your weight while taking olanzapine. They can review strategies to help you lose weight gained from your medication.

Below is important information you should consider before taking olanzapine oral tablet.

Olanzapine has a boxed warning. A boxed warning is the most serious warning from the FDA. For details, see the “Olanzapine: Side effect specifics” section.

Other precautions

Before taking Olanzapine, discuss your health history with your doctor. Olanzapine may not be right for you if you have certain medical conditions or other factors affecting your health. Be sure to talk with your doctor if any of the following apply to you:

Disclaimer: Medical News Today has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.