Like all medicines, olanzapine can cause side effects, although not everyone gets them.
Common side effects of olanzapine
These common side effects of olanzapine may affect up to 1 in 10 people. There are things you can do to help cope with them:
Feeling sleepy in the day
Do not drive, cycle or use tools or machinery if you're feeling this way. Do not drink alcohol as this will make you feel more tired.
As your body gets used to olanzapine, these side effects should wear off. Speak to your doctor if they get worse or do not go away.
Putting on weight or an increase in your appetite
Try to eat a healthy, balanced diet without increasing your portion sizes. Do not snack on foods that contain a lot of calories, such as crisps, cakes, biscuits and sweets. If you feel hungry between meals, eat fruit and vegetables and low-calorie foods.
Regular exercise will also help to keep your weight stable.
Feeling dizzy
If olanzapine makes you feel dizzy when you stand up, get up slowly and hold on to something to steady your balance until your dizziness has passed. It should only last a few moments.
As your body gets used to your medicine this problem should get better.
Rash
It may help to take an antihistamine, which you can buy from a pharmacy. Ask your pharmacist which type is suitable for you to take while you're on olanzapine.
Constipation
Eat more high-fibre foods such as fresh fruit, vegetables and cereals. Try to drink several glasses of water or another non-alcoholic liquid every day. Try to exercise more regularly, for example, by going for a daily walk or run.
Speak to a doctor or pharmacist if the advice on how to cope does not help and a side effect is still bothering you or does not go away.
See your doctor if you have sexual problems such as lower libido in men or women, or problems getting an erection. These can be signs of hormone changes.
Serious side effects
Serious side effects are rare and happen in less than 1 in 1,000 people.
Call your doctor or call 111 for advice now if:
- you get infections including coughs, colds and chest infections, ear and eye infections, or urinary tract infections (UTIs) – these can be signs of a low white blood cell count
- you get swelling, pain and redness in one leg – these can be signs of blood clots
- you get twitching or jerking movements in your face, tongue or other parts of your body
- you have difficulty walking or start shuffling slowly when you walk, trembling or shaking
Immediate action required: Call 999 or go to A&E if:
- you get chest pain or difficulty breathing – these may be signs of blood clots
- you have weakness on one side of your face or body, trouble speaking or thinking, or blurred eyesight – these can be signs of a stroke
- you have a high temperature, muscle stiffness, sweating, anxiety or excess saliva – these can be signs of a disorder called neuroleptic malignant syndrome
- you get a painful erection (priapism) lasting more than 3 to 4 hours, or more than 1 hour if you have sickle cell disease
Serious allergic reaction
In rare cases, it's possible to have a serious allergic reaction (anaphylaxis) to olanzapine.
Immediate action required: Call 999 now if:
- your lips, mouth, throat or tongue suddenly become swollen
- you're breathing very fast or struggling to breathe (you may become very wheezy or feel like you're choking or gasping for air)
- your throat feels tight or you're struggling to swallow
- your skin, tongue or lips turn blue, grey or pale (if you have black or brown skin, this may be easier to see on the palms of your hands or soles of your feet)
- you suddenly become very confused, drowsy or dizzy
- someone faints and cannot be woken up
- a child is limp, floppy or not responding like they normally do (their head may fall to the side, backwards or forwards, or they may find it difficult to lift their head or focus on your face)
You or the person who's unwell may also have a rash that's swollen, raised, itchy, blistered or peeling.
These can be signs of a serious allergic reaction and may need immediate treatment in hospital.
Do not drive yourself to A&E.
The person you speak to at 999 will give you advice about what to do.
Long-term side effects
Olanzapine can increase the amount of sugar in your blood and this can sometimes lead to diabetes. This affects less than 1 in 100 people. Keeping to a healthy weight can help to prevent it.
You'll usually have blood tests before starting olanzapine and while you're taking it to check your blood sugar.
If you already have diabetes you'll be monitored more closely and will have more regular blood sugar tests.
Taking olanzapine for a long time can sometimes affect your cholesterol. If this happens, your doctor may advise you to take a medicine to help lower your cholesterol.
Other side effects
These are not all the side effects of olanzapine. For a full list see the leaflet inside your medicines packet.
Reporting side effects
You can report any suspected side effect using the Yellow Card safety scheme.
Visit the Yellow Card website for more information about reporting side effects.