Your doctor will talk to you about this treatment and its possible side effects before you agree (consent) to have treatment.
Osimertinib comes as tablets. This means you can take it at home.
During treatment you usually see a:
- cancer doctor
- cancer nurse or specialist nurse
- specialist pharmacist.
This is who we mean when we mention doctor, nurse or pharmacist in this information.
You will have regular blood tests before and during treatment. A nurse or person trained to take blood (phlebotomist) will take a blood sample from you to check that it is safe for you to have treatment.
Your course of treatment
Your doctor, nurse or pharmacist will discuss your treatment plan with you.
You usually continue to take osimertinib for as long as it is working for you and side effects can be managed. Do not stop taking it without your doctor’s advice.
Taking osimertinib tablets
You take osimertinib once a day. Your doctor, nurse or pharmacist will tell you how many tablets to take. Always take them exactly as you are told to. This is important to make sure they work as well as possible for you.
Osimertinib can be taken with or without food. You should try to take your tablets at the same time each day. Swallow them whole with water. Do not chew, break or crush them.
If you cannot swallow the tablets, you can dissolve them in a small amount of water. Drop them into 50ml of water and stir until they dissolve. Drink this straight away. Half-fill the glass with water again and drink this too.
If you forget to take your tablets, do not take a double dose. If there are more than 12 hours until your next dose, take your tablets as soon as you remember.
If there are less than 12 hours until your next dose, do not take any tablets. Take your next dose at the usual time and let your doctor or nurse know.
Other things to remember about your tablets:
- Keep them safe, somewhere that children cannot see or reach them.
- Keep them in the original package and at room temperature, away from moisture, heat and direct sunlight.
- It is important to get a new prescription before you run out of tablets or capsules. Make sure you have plenty for holidays.
- If you are sick just after taking the tablets, contact the hospital. Do not take another dose.
- If your treatment is stopped, return any unused tablets to the pharmacist
We explain the most common side effects of this treatment here. We also include some less common side effects.
You may get some of the side effects we mention, but you are unlikely to get all of them. If you are also having treatment with other cancer drugs, you may have some side effects that we have not listed here. Always tell your doctor, nurse or pharmacist about any side effects you have.
Your doctor can give you drugs to help control some side effects. It is important to take them exactly as your nurse or pharmacist explains. This means they will be more likely to work for you. Your nurse will give you advice about managing your side effects. After your treatment is over, most side effects start to improve.
Serious and life-threatening side effects
Some cancer treatments can cause severe side effects. Rarely, these may be life-threatening. Your cancer doctor or nurse can explain the risk of these side effects to you.
Contact the hospital
Your nurse will give you telephone numbers for the hospital. If you feel unwell or need advice, you can call them at any time of the day or night. Save these numbers in your phone or keep them somewhere safe.
We cannot list every side effect for this treatment. There are some rare side effects that are not listed. You can visit the electronic Medicines Compendium (eMC) for more detailed information.
Risk of infection
This treatment can reduce the number of white blood cells in your blood. These cells fight infection. If the number of white blood cells is low, you are more likely to get an infection. A low white blood cell count is sometimes called neutropenia.
An infection can be very serious when the number of white blood cells is low. It is important to get any infection treated as soon as possible. Contact the hospital straight away on the 24-hour contact number you have been given if:
- your temperature goes over 37.5°C (99.5°F)
- you suddenly feel unwell, even with a normal temperature
- you have symptoms of an infection
- your temperature goes below 36°C (96.8°F).
Symptoms of an infection include:
- feeling shivery and shaking
- a sore throat
- a cough
- needing to pass urine (pee) a lot, or discomfort when you pass urine.
It is important to follow any specific advice your cancer treatment team gives you.
You will have regular blood tests during treatment. If needed, your doctor may reduce or delay your treatment for a short time, until your cell count increases.
Bruising and bleeding
This treatment can reduce the number of platelets in your blood. Platelets are cells that help the blood to clot.
If the number of platelets is low, you may bruise or bleed easily. You may have:
- bleeding gums
- heavy periods
- blood in your urine (pee) or stools (poo)
- tiny red or purple spots on the skin that may look like a rash.
Tell your doctor if you have any unexplained bruising or bleeding. You may need a drip to give you extra platelets. This is called a platelet transfusion.
This treatment may cause diarrhoea. Diarrhoea means passing more stools (poo) than is usual for you, or having watery or loose stools. If you have a stoma, it will be more active than usual.
If you have diarrhoea:
- try to drink at least 2 litres (3½ pints) of fluids each day
- avoid alcohol, caffeine, milk products, high-fat foods and high-fibre foods
- contact the hospital for advice.
This treatment can cause a rash and a dry skin. Usually this is mild. Sometimes this can be itchy. Tell your doctor or nurse if you have any skin changes. They can give you advice, creams and drugs to help.
Very rarely, a much more serious skin condition can develop. You may have a skin rash which then blisters, and your skin can peel. You may also feel unwell with flu-like symptoms, such as a high temperature and joint pain. If you have any of these symptoms, contact your doctor or hospital immediately.
You may notice changes to your nails. They may:
- become brittle
- break easily
- become infected.
Wear gloves when washing dishes or using detergents to help protect your hands and nails. Dry your hands carefully after washing. If the area around your nails becomes red, hot or swollen, tell your doctor straight away. They can give you advice and treatment to help.
You may get a sore mouth or mouth ulcers. This is usually mild, but can make you more likely to get a mouth infection. Use a soft toothbrush to clean your teeth or dentures in the morning, at night and after meals.
If your mouth is sore:
- tell your nurse or doctor – they can give you a mouthwash or medicines to help
- try to drink plenty of fluids
- avoid alcohol, tobacco, and foods that irritate your mouth.
Effects on the lungs
Rarely, this treatment can cause unexpected and sudden changes to the lungs. Sometimes this can be serious. Always tell your doctor if you develop:
- a cough
- a fever (high temperature)
You should also tell them if any existing breathing problems get worse. Your doctor may tell you to stop taking osimertinib while you have tests to check your lungs. You may need treatment if you have this side effect.
Effects on the eyes
Osimertinib may affect your eyes or eyesight. Tell your doctor or nurse if your:
- eyes are sore, red, watery
- eyes feel sensitive to light
- eyesight is blurry.
They may arrange for you to see an eye doctor (ophthalmologist) for more advice. Your doctor may tell you to stop taking osimertinib for a short time until this side effect improves.
Effects on the heart
This treatment can affect how the heart works. You may have tests to see how well your heart is working. These may be done before, during and after treatment.
If the treatment is causing heart problems, your doctor may change the type of treatment you are having.Contact your doctor straight away on the 24-hour number the hospital has given you if you have any of these symptoms during or after treatment:
- pain or tightness in your chest
- changes to your heartbeat.
Other conditions can cause these symptoms, but it is important to get them checked by a doctor. If you cannot get through to your doctor, call the NHS urgent advice number on 111.
Sore and red palms of hands and soles of feet
You may get sore and red palms of hands and soles of feet. The skin may also begin to peel. This is called palmar-plantar or hand-foot syndrome. It usually gets better after treatment ends.
Tell your doctor or nurse about any changes to your hands or feet. They can give you advice and prescribe creams to improve any symptoms you have. It can help to:
- keep your hands and feet cool
- moisturise your hands and feet regularly
- avoid tight-fitting socks, shoes and gloves.
Effects on the kidneys
This treatment can affect how your kidneys work. This is usually mild and goes back to normal after treatment finishes. You will have blood tests to check how well your kidneys are working. Tell your doctor or nurse if you have blood in your urine (pee) or you are passing urine less than usual.
It is important to drink at least 2 litres (3½ pints) of non-alcoholic fluid each day to help protect your kidneys.
Your hair may become thinner when you are taking this treatment. This is usually mild. Ask your nurse for advice if you are worried about this.
Blood clot risk
Cancer and some cancer treatments can increase the risk of a blood clot. Symptoms of a blood clot include:
- throbbing pain, redness or swelling in a leg or arm
- suddenly feeling breathless or coughing
- sharp chest pain, which may be worse when you cough or take a deep breath.
If you have any of these symptoms, contact the hospital straight away on the 24-hour contact number you have been given. If you cannot get through to your doctor, call the NHS urgent advice number on 111.
A blood clot is serious, but it can be treated with drugs that thin the blood (anticoagulants). Your doctor or nurse can give you more information.
You can help reduce the risk of developing a blood clot by:
- staying active during treatment
- drinking plenty of fluids, especially water.
You may be given anticoagulants to help prevent a clot.
Some medicines can affect how this treatment works or be harmful when you are having it. Always tell your cancer doctor about any drugs you are taking or planning to take, such as:
- medicines you have been prescribed
- medicines you buy in a shop or chemist
- vitamins, herbal drugs and complementary therapies.
Tell other doctors, pharmacists or dentists who prescribe or give you medicines that you are having this cancer treatment.
You can visit the electronic Medicines Compendium (eMC) for more detailed information about your treatment.
Vaccinations can reduce your risk of getting certain infections. Your doctor or nurse may talk to you about having vaccinations.
Doctors usually recommend that people with cancer have a flu vaccination and a coronavirus (covid) vaccination. These are both inactivated vaccinations that can help reduce the risk of infection. People with weak immune systems can have these, as they are not live vaccinations.
If your immune system is weak, you need to avoid live vaccinations. This is because they can make you unwell. Live vaccines contain a very weak version of the illness they are vaccinating you against. Your cancer doctor or GP can tell you more about live and inactivated vaccinations.
Your doctor will advise you not to get pregnant or make someone pregnant while having this treatment. The drugs may harm a developing baby. It is important to use contraception during your treatment and for a while after treatment finishes. Your doctor, nurse or pharmacist can tell you more about this.
If you take the contraceptive pill, it may not be as effective while you are taking osimertinib.
You are advised not to breastfeed while having this treatment, or for some time after treatment finishes. This is because the drugs could be passed to the baby through breast milk.
Your doctor or nurse can give you more information.
Medical and dental treatment
If you need medical treatment for any reason other than cancer, always tell the doctors and nurses you are having cancer treatment. Give them the contact details for your cancer doctor so they can ask for advice.
If you think you need dental treatment, talk to your cancer doctor or nurse. Always tell your dentist you are having cancer treatment.
This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert health professionals and people living with cancer.
Our cancer information has been awarded the PIF TICK. Created by the Patient Information Forum, this quality mark shows we meet PIF’s 10 criteria for trustworthy health information.
The language we use
We want everyone affected by cancer to feel our information is written for them.
We want our information to be as clear as possible. To do this, we try to:
- use plain English
- explain medical words
- use short sentences
- use illustrations to explain text
- structure the information clearly
- make sure important points are clear.
We use gender-inclusive language and talk to our readers as ‘you’ so that everyone feels included. Where clinically necessary we use the terms ‘men’ and ‘women’ or ‘male’ and ‘female’. For example, we do so when talking about parts of the body or mentioning statistics or research about who is affected.
You can read more about how we produce our information here.
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