Olanzapine: uses, side effects and blood tests

Olanzapine is an antipsychotic that works by affecting chemicals in the brain such as dopamine and serotonin. In schizophrenia it targets symptoms such as seeing, hearing, feeling or believing things that others do not. In bipolar disorder it manages manic episodes and helps prevent them returning.

The NHS is clear that it does not cure the condition, but it can help with symptoms. Some people feel calmer within days, before other symptoms begin to improve over several days or weeks.

Tablets come in a range of strengths, and there are orodispersible tablets that you place on your tongue or mix into water, juice or milk. Injections are given into a muscle every 2 to 4 weeks at a specialist clinic.

It is taken once daily at around the same time, with or without food. The NHS gives typical starting points of 10 mg a day for schizophrenia, 15 mg for mania (or 10 mg if taking other medicines) and 10 mg to prevent mania, with the usual effective range 5 mg to 20 mg. Lower starting doses are used in older people or those with kidney or liver problems. Your own dose will be set by your prescriber.

If you miss a dose, take it when you remember unless the next dose is due, and skip it if you remember the next day. Contact your doctor if you miss two or more doses.

The NHS says common side effects affect up to 1 in 10 people. Practical advice follows each.

• Sleepiness: do not drive, cycle or use machinery while affected, and avoid alcohol.

• Weight gain or bigger appetite: balance your diet, avoid large portions and high-calorie snacks, and exercise regularly.

• Dizziness: get up slowly and hold on to something steady.

• Constipation: eat more fibre, drink water and keep active.

• Sexual problems such as lower libido or erectile difficulty: speak to your doctor, as these can reflect hormone changes.

Rare serious effects are listed by urgency. Call NHS 111 for repeated infections (possible low white blood cells), a swollen, painful or red leg, twitching or jerking of the face or tongue, or walking difficulties, shuffling or trembling.

Call 999 or go to A&E for chest pain or breathing difficulty, stroke signs, high temperature with stiff muscles, sweating, anxiety and excess saliva (possible neuroleptic malignant syndrome), or a painful erection lasting several hours. Anaphylaxis also needs 999.

Olanzapine can raise blood sugar and may lead to diabetes in fewer than 1 in 100 people. Because of that, blood tests are needed before and during treatment. It may also affect cholesterol, and your doctor may prescribe cholesterol medicine. The NHS says people will not usually lose weight on olanzapine.

Tell the prescriber about heart problems, low blood pressure, stroke risk, blood clots, Parkinson's disease, dementia, low white cell counts, diabetes, epilepsy, liver or kidney problems, glaucoma, severe constipation or high prolactin levels.

Named interactions include carbamazepine, fluvoxamine, ciprofloxacin, benzodiazepines, morphine, tramadol and chlorphenamine, with sedating effects adding up. The NHS says not to take cannabidiol (CBD).

The NHS says olanzapine is not thought to be harmful to the baby in pregnancy and that treatment should not be stopped without advice. It passes into breast milk in small amounts; do not bed-share with your baby.

Avoid alcohol in the first few days; regular drinking can worsen symptoms. Never stop abruptly: the dose is reduced gradually to prevent nausea, sweating and sleeplessness. Report suspected side effects to the MHRA Yellow Card scheme.