Medication guide

Olanzapine (Zyprexa)

What is olanzapine?

Olanzapine is known as Zyprexa in the United States, the UK, and Japan alike (ジプレキサ on Japanese packaging). It's a medication in the family called antipsychotics: it works mainly by calming overactive dopamine signalling in the brain, with broader receptor actions that give it its settling effect on sleep and appetite. It's one of the stronger, most reliable calming options in its group, and it also tends to settle sleep and appetite.

How is it different from other antipsychotics?

Strong and dependable: a first-call option for severe episodes, with decades of worldwide evidence
Covers both poles of bipolar disorder: approved in Japan for manic and depressive episodes alike
Settles sleep and appetite from early on, which often matters as much as the main effect
Once nightly, simple to live with

What is it used for in Japan?

Schizophrenia
Bipolar disorder: both manic and depressive episodes
Nausea from certain cancer treatments (a separate, non-psychiatric use)

How does it help?

By calming overactive dopamine signalling, it eases symptoms and stabilises mood over time. The full effect builds over a few weeks; keep taking it as prescribed even if you don't notice a change straight away.

What should I tell my doctor before starting?

A few situations rule it out entirely; your doctor will choose something else if any of these apply:

Diabetes, or a history of diabetes: olanzapine isn't used in this case, as it can raise blood sugar to dangerous levels
A past allergic reaction to olanzapine
Being under the strong influence of sedatives, sleeping-drug overdose, or anesthesia (a coma-like or deeply sedated state)
Treatment with adrenaline (epinephrine), except emergency allergy injections and some dental anesthesia

And tell your doctor first if any of these apply; these usually just need adjustments or a closer eye:

A family history of diabetes, or borderline blood sugar
Other sedating medicines, or regular alcohol use
A history of seizures
Being older
Pregnant, planning to be, or breastfeeding (see the section below)

Even without diabetes, your blood sugar and weight are checked during treatment.

How do I take it, and what if I miss a dose?

Olanzapine is taken once a day, often at night; its calming effect works with your sleep. (For the depressive episodes of bipolar disorder, bedtime dosing is how the label specifies it.)

If you miss a dose: just skip it if the next one is close. Never take a double dose to catch up
Weight and appetite are the things to watch from early on; weighing regularly and telling your doctor beats discovering it months later

What side effects should I expect?

Most are manageable and settle as your body adjusts, and many can be eased with a counter-medicine if needed. Not everyone gets them; the rough figures below just give a sense of how common each one is.

Drowsiness (around 20%): often folded into bedtime by night dosing
Weight gain (around 20%), often with a bigger appetite: the main one to stay ahead of, with regular weighing
Trouble sleeping (around 10%)
Dry mouth, or constipation
A rise in blood fats (cholesterol or triglycerides): part of why blood tests are done
Dizziness or light-headedness on standing: get up slowly at first

If anything is bothering you, tell your doctor; there's often a way to adjust. And if you ever feel worse instead of better, tell us straight away; it's easily managed, and that's what we're here for.

Finally, two things that are rare (most people never experience them) but good to know:

A lot of thirst, drinking, or passing urine much more than usual: these can signal a serious rise in blood sugar; stop the medicine and see a doctor promptly, and it's caught with the routine checks
A combination of high fever, muscle stiffness, and confusion (on the order of 1 in 1,000 people or fewer): get medical care promptly; recognised early, it's manageable

Will I become dependent? How do I stop safely?

No; olanzapine isn't addictive and doesn't cause cravings. Stopping is about timing rather than withdrawal: coming off too early can let symptoms return, so the decision and the pace are planned with your doctor. Don't stop it on your own, even when you feel well.

Can I drive while taking it?

The Japanese label advises against driving while taking it. Olanzapine's drowsiness is real, especially early on and at night-dose timing, and the label here instructs that patients on it shouldn't drive or operate dangerous machinery. Discuss your own situation with your doctor.

What about pregnancy and breastfeeding?

Often, treatment can continue when it's needed; the decision is individual. Untreated illness carries real risks in pregnancy too, so this is a planning conversation, not an automatic stop; never stop on your own on learning you're pregnant. Breastfeeding is decided case by case. Our guides to medication in pregnancy and medication while breastfeeding cover the details.