Olanzapine: what it treats, how to take it, side effects
Last updated September 3, 2026.
Olanzapine is an atypical antipsychotic - it changes the activity of certain natural substances in the brain. You may know it as Zyprexa. It is one of the most effective medicines for schizophrenia and bipolar mania, and one of the ones that asks the most in return: it deserves an honest conversation about weight and blood sugar.
What does it treat?
Schizophrenia and bipolar I disorder, the manic or mixed episodes, in adults and teenagers 13 and older - sometimes combined with fluoxetine for bipolar depression. It controls symptoms but does not cure the condition, and the full benefit can take several weeks to arrive.
How do you take it?
Once a day, with or without food, same time every day. The label starts most adults at 5 to 10 mg, targets 10 mg within several days, and adjusts no faster than weekly - the medicine takes about a week to reach steady levels. If you use the orally disintegrating tablets: dry hands, peel the foil back (never push the tablet through it), and let it dissolve on your tongue. Keep taking it when you feel well, and never stop without your doctor. Missed dose: take it when you remember unless the next one is close; never double up.
Side effects to know
- Common: increased appetite and weight gain, dry mouth, constipation, drowsiness, restlessness, weakness, dizziness on standing, and breast enlargement or discharge.
- Serious - call your doctor immediately: unusual movements of the face or body you cannot control; fever with stiff muscles, sweating, confusion, or a fast or irregular heartbeat (neuroleptic malignant syndrome); seizures; signs of infection like fever, sore throat, or chills; a rash with fever, swollen glands, or facial swelling; hives or skin peeling; and high blood sugar - extreme thirst, frequent urination, extreme hunger, blurred vision, or weakness, which can become ketoacidosis (fruity-smelling breath, vomiting, shortness of breath, decreased consciousness).
Who should not take it?
The boxed warning: older adults with dementia have an increased risk of death and stroke on antipsychotics, and olanzapine is not approved for dementia-related behavior disorders. Flag diabetes or family diabetes, high cholesterol, heart problems, stroke or mini-stroke history, seizures, low white blood cell counts, glaucoma, and liver or prostate disease. Teenagers gain more weight on it than adults and see more metabolic and liver effects - the trade-off needs the whole family in the room. Smoking lowers how well it works, so tell your doctor if you use tobacco. The disintegrating tablets contain aspartame, which matters if you have PKU. Common antihistamines and omeprazole interact - mention them. Alcohol adds to the drowsiness: do not drink while taking it. Ask about grapefruit. Overheating is easier on this medicine - pace yourself in hot weather. If you become pregnant, call your doctor.
When is it an emergency?
Fever with stiff muscles and confusion, a seizure, or fainting is a 911 call. Facial swelling with trouble breathing, or a spreading rash with fever, is also emergency territory. For an overdose - drowsiness, slurred speech, agitation, uncontrollable movements - call Poison Control at 1-800-222-1222. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper.
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Common questions
Why does olanzapine cause weight gain?
Increased appetite and weight gain are on the common-effects list, and MedlinePlus notes teenagers gain more than adults. The medicine changes brain signaling that touches hunger and metabolism - the same system that steadies mood. The practical answer: your prescriber tracks weight, blood sugar, and cholesterol from the start, because the metabolic shift is expected and manageable when it is watched.
Why does olanzapine carry a boxed warning?
The label's boxed warning: older adults with dementia have an increased risk of death - and a greater chance of stroke - when treated with antipsychotics. Olanzapine is not approved for behavior problems in older adults with dementia. If someone you care for has dementia and was prescribed it, that is a direct conversation with the prescriber.
Why can't I smoke on olanzapine?
You can - but your doctor needs to know, because MedlinePlus says cigarette smoking may decrease the effectiveness of the medication. Smoke changes how the liver processes olanzapine, so smokers can need different dosing. It is a dosing fact for your prescriber, not a lecture from us.
How do I take the dissolving olanzapine tablet?
Dry hands first. Peel back the foil - never push the tablet through it, it crumbles - place it on your tongue, and let it dissolve; swallow with or without liquid. Use it immediately after opening the package. If you have PKU, tell your prescriber: these tablets contain aspartame, which becomes phenylalanine.
Can I drink alcohol while taking olanzapine?
No - MedlinePlus says it directly: alcohol can add to the drowsiness this medication causes, so do not drink while taking it. The combination deepens sedation and the fall risk that comes with the dizziness this drug can cause when you stand up.
What happens if I miss a dose of olanzapine?
Take it as soon as you remember, unless it is almost time for the next one - then skip it and never double up. It is a once-daily medicine, so the easiest anchor is a fixed time - most people pick bedtime, which also puts the drowsiness to work.