Olanzapine (Zyprexa)

What it treats

Olanzapine is approved by the U.S. Food and Drug Administration to treat schizophrenia and bipolar I disorder, including acute manic and mixed episodes, and as maintenance treatment for bipolar I. In combination with fluoxetine (sold as Symbyax), it is also approved for treatment-resistant depression and for bipolar depression. A short-acting intramuscular form is used for acute agitation in the emergency setting.

Olanzapine is often chosen when a strong, dependable response is needed early, for example during a hospital admission for mania or a first episode of psychosis. It is not usually a first choice for someone with high metabolic risk or an already-elevated BMI, because of the side-effect profile below.

How it works

Olanzapine is an atypical antipsychotic. It works by dampening the activity of several brain chemical messengers at once, dopamine, serotonin, histamine, and others. That broad action is thought to underlie both its strong effect on psychosis and mania and its side-effect pattern. Effects build over days to weeks. Some effects, such as sedation, are noticeable within hours.

The exact reason it works so reliably for mania and psychosis is not fully settled. What is clear from decades of use is that, at adequate doses, it reduces hallucinations, delusions, and disorganized thinking, and it settles manic symptoms, often faster than several alternatives.

Receptor mechanism (detail)

Olanzapine is a multi-receptor antagonist. It blocks dopamine D2, serotonin 5-HT2A and 5-HT2C, histamine H1 (strongly), muscarinic M1 to M5 receptors (strongly), and α1-adrenergic receptors. The strong H1 and 5-HT2C blockade are the main drivers of appetite increase and weight gain. The strong muscarinic blockade explains dry mouth, constipation, and some of the cognitive slowing that some people notice. The D2 and 5-HT2A blockade drive the antipsychotic and antimanic effect.

Potency and typical dosing pattern

Ranges are typical framework only, not a prescription for any individual. Olanzapine is moderate potency by milligram.

For schizophrenia, a typical starting dose is 5 to 10 mg once daily, adjusted to a usual maintenance range of 10 to 20 mg once daily. For acute mania, starting doses often sit at 10 to 15 mg once daily. Olanzapine is also available as Zydis, an orally disintegrating tablet, which can be useful when a person is unable or unwilling to swallow a standard tablet. The long-acting injectable form, Zyprexa Relprevv, is given every two weeks at 150 to 300 mg by a clinician and requires a post-injection observation period because of a rare post-injection delirium and sedation syndrome.

Safety monitoring

Because olanzapine carries meaningful metabolic risk, monitoring is tighter than with lower-risk antipsychotics.

• Weight, waist circumference, and BMI at baseline, then at weeks 4, 8, and 12, and quarterly after that.
• Fasting glucose or HbA1c and a lipid panel at baseline, at three months, and every three to six months during ongoing treatment. This is stricter than the annual schedule used with lower-risk medications and reflects olanzapine's higher metabolic footprint.
• Blood pressure at baseline and periodically.
• Movement effects. Ask about restlessness (akathisia) and stiffness early on. An involuntary-movement screen (AIMS) every six months looks for tardive dyskinesia over the long term.
• Prolactin only if symptoms suggest it, olanzapine usually causes only mild prolactin elevation.

Metformin co-commencement. Aoife Carolan / Schizophrenia Bulletin guideline.

A clinical guideline led by Aoife Carolan strongly recommends co-commencing metformin alongside high-risk antipsychotics like olanzapine or clozapine. This proactive approach helps mitigate severe metabolic side effects, significantly reducing antipsychotic-induced weight gain and improving insulin resistance. The Schizophrenia Bulletin guideline states that when prescribing olanzapine or clozapine, metformin should be initiated immediately to prevent weight gain and cardiometabolic issues.

Typical titration used in the guideline: 500 mg once daily → 500 mg twice daily after one week → 500 mg increments every two weeks as tolerated → up to 1000 mg twice daily by about week six. Contraindicated with eGFR below 30 mL/min/1.73 m²; renal function is checked annually and metformin is held during acute illness or dehydration.

Source: Carolan A, et al. Metformin for the Prevention of Antipsychotic-Induced Weight Gain: Guideline Development and Consensus Validation. Schizophrenia Bulletin. 2025;51(5):1193 to 1203.

What to expect

Common side effects

Most people experience some side effects. The common ones include:

• Sedation and drowsiness, especially early on.
• Increased appetite and weight gain.
• Dry mouth.
• Constipation.
• Dizziness, especially on standing up.
• Mild tremor or slowed movement in some people.

Weight and appetite changes deserve honest early attention. Small habits set early, regular meals, movement, sleep timing, matter more here than with lower-risk antipsychotics. If a side effect is severe or not improving, that is a conversation to have with the prescriber rather than a reason to stop on your own.

Serious side effects and warnings

Serious problems are uncommon, but a few are worth knowing.

Boxed warning. Like all antipsychotics, olanzapine carries an FDA boxed warning that it increases the risk of death in older adults with dementia-related psychosis, and antipsychotics are not approved for that use. The long-acting injectable form (Zyprexa Relprevv) carries an additional boxed warning about post-injection delirium and sedation syndrome, described below.

• Metabolic effects. Olanzapine has one of the stronger effects on weight, blood sugar, and lipids among the atypicals. Ongoing metabolic monitoring, and often lifestyle or medication support, is part of using it.
• Tardive dyskinesia. A movement disorder linked to long-term antipsychotic use, involving repetitive involuntary movements, often of the face or mouth. The risk rises with longer use.
• Neuroleptic malignant syndrome. A rare but serious reaction. Signs include high fever, muscle stiffness, confusion, and unstable heart rate or blood pressure. It is a medical emergency.
• Post-injection delirium and sedation syndrome (LAI only). With Zyprexa Relprevv, a small fraction of injections can cause a sudden episode of severe sedation, confusion, or delirium within a few hours. That is why the injection must be given in a healthcare setting and followed by three hours of observation before the person leaves.
• Orthostatic hypotension and falls, especially in older adults.

Sexual side effects

Sexual side effects, lower desire, difficulty with arousal or orgasm, can occur with olanzapine, though rates tend to be lower than with medications that raise prolactin more. If they occur and are bothersome, that is worth raising with the prescriber rather than living with it, because there are usually options.

Weight, appetite, and sleep

Weight gain is the side effect people most often ask about with olanzapine, and it is real. Average weight gain in the first months can be several kilograms, with wide variation. Appetite tends to increase, particularly for high-carbohydrate foods, and satiety cues can feel muted. Setting up routines around meals, movement, and sleep early, before habits form around the appetite change, makes a real difference. Weight, blood sugar, and lipids are tracked over time, and for many people a paired metformin plan is discussed at the start.

Olanzapine is sedating for most people, and it is usually taken in the evening for that reason. Sleep quality often improves.

Starting and dosing basics

This section is general background, not a dosing instruction for any individual. The right dose is a decision for a prescriber.

Olanzapine comes as tablets, orally disintegrating tablets (Zydis), a short-acting intramuscular injection for acute agitation, and a long-acting injection (Zyprexa Relprevv) given by a clinician. It can be taken with or without food. It is usually taken in the evening because of sedation.

Missed doses and interactions

If you miss a dose, the general guidance is to take it when you remember, unless it is almost time for the next dose. In that case, skip the missed dose and carry on. Don't take two doses to make up for one.

Smoking speeds up how the body clears olanzapine, so smokers often need higher doses and levels can rise if smoking stops abruptly. That is worth mentioning to the prescriber if smoking status changes. Other medications can also affect olanzapine levels. The prescriber and pharmacist need a full list of your medications and supplements, including over-the-counter ones. Alcohol is not formally prohibited, but it can worsen sedation and is generally best limited. This is not medical advice.

Stopping and tapering

Stopping olanzapine should be gradual and planned with a prescriber. The body adjusts to the medication over time, and stopping suddenly can cause rebound insomnia, nausea, and a return of the underlying symptoms. A prescriber can step the dose down over time in a way that fits the situation.

Pregnancy and breastfeeding

This is an area where individual circumstances matter and the decision belongs with a clinician. Untreated bipolar disorder and psychosis carry their own risks during pregnancy, and olanzapine also passes into breast milk. Anyone who is pregnant, planning a pregnancy, or breastfeeding should talk it through with their prescriber so the specific risks and benefits can be weighed for their situation.

Cost and generic availability

Olanzapine has been available as a generic for years and is inexpensive. The brand name Zyprexa and generic olanzapine contain the same active medication and work the same way. The long-acting injectable form and the Symbyax combination cost more than plain generic tablets. Most insurance plans cover the generic.

Common questions

Why is olanzapine still used given the metabolic risks? Because it works. For acute mania, first-episode psychosis, and treatment-resistant symptoms, olanzapine is one of the most reliably effective atypical antipsychotics available. When the alternative is untreated psychosis or mania, the metabolic risk is managed rather than avoided.

What is post-injection syndrome? Post-injection delirium and sedation syndrome is a rare reaction to the Zyprexa Relprevv long-acting injection, in which a small amount of the medication reaches the bloodstream quickly and causes severe sedation or confusion within a few hours. It is why the injection is given in a clinic and followed by three hours of observation before the person goes home.

Should I take metformin with it? For many people started on olanzapine, yes. The Carolan guideline recommends co-commencing metformin with high-risk antipsychotics including olanzapine to blunt weight gain and metabolic change. Whether that fits your situation is a decision to make with your prescriber.

Will I definitely gain weight? Weight gain is common but not universal. Habits set early, around meals, movement, and sleep, make a meaningful difference. Metabolic labs are tracked over time so changes are caught early rather than late.

Questions to ask your prescriber

• What are we hoping this treats, and how will we know it's working?
• Should we start metformin at the same time given the metabolic risk?
• Which side effects should I expect early, and which ones should I call about?
• How will we track weight, blood sugar, and lipids?
• If we decide to stop it later, how would we do that safely?

Sources

This guide draws on current prescribing information and public health references. It is reviewed for clinical accuracy and updated as guidance changes. Guidelines and prescribing information reviewed and current as of June 8, 2026.

• U.S. Food and Drug Administration. Olanzapine (Zyprexa) prescribing information (DailyMed).
• MedlinePlus, U.S. National Library of Medicine. Olanzapine.
• National Institute of Mental Health. Mental health medications.
• American Psychiatric Association. Practice Guideline for the Treatment of Patients with Schizophrenia, 3rd edition.
• National Institute for Health and Care Excellence (NICE). CG178, Psychosis and schizophrenia in adults.
• American Diabetes Association / American Psychiatric Association. Consensus Statement on Antipsychotic Drugs and Obesity and Diabetes.
• Carolan A, et al. Metformin for the Prevention of Antipsychotic-Induced Weight Gain: Guideline Development and Consensus Validation. Schizophrenia Bulletin. 2025;51(5):1193 to 1203.