What is selpercatinib (Retsevmo®)?

Selpercatinib (Retsevmo®) is a targeted drug used to treat advanced non-small cell lung cancer, advanced thyroid cancer and advanced medullary thyroid cancer (MTC). It is best to read this information with our general information about the type of cancer you have. 

Selpercatinib belongs to a group of targeted therapy drugs known as cancer growth inhibitors. It can only be used to treat cancers that have a change in a gene called RET. The gene change encourages the cancer cells to grow and divide. Selpercatinib blocks the effect of the gene change and slows or stops the cancer cell growth. 

You will have tests on the cancer cells to check for the gene change. This tells your doctor whether selpercatinib is suitable for you.

Your doctor will talk to you about this treatment and its possible side effects before you agree (consent) to have treatment.

More information about this treatment

This information is correct at time of publishing. But sometimes the types of cancer this treatment is used for, or treatment side effects, may change between revision dates.

You can talk to your cancer team if you want more detailed information about this treatment. Or visit the electronic Medicines Compendium (eMC) website, which has patient information leaflets (PIL) for individual drugs.

How selpercatinib is given

Selpercatinib comes as capsules, so you can take them at home. During treatment you usually see a cancer doctor, a cancer nurse or specialist nurse, and a specialist pharmacist. This is who we mean when we mention doctor, nurse or pharmacist in this information.

During treatment you will have regular blood samples taken. This is to check things such as:

  • the level of your blood cells
  • how well your liver and kidneys are working.

Your doctor, nurse or pharmacist will discuss your treatment plan with you. They will explain how to take selpercatinib. You may be given other medicines to take home. Take all your medicines exactly as your doctor or pharmacist tell you.

You usually carry on taking selpercatinib for as long as it is working for you and any side effects can be managed. Do not stop taking selpercatinib without talking to your doctor first.

Taking selpercatinib capsules

You take selpercatinib capsules twice a day. Capsules should be taken at the same time every day in the morning and evening. Swallow the capsule whole with a glass of water. They should not be chewed, opened or crushed.

You can usually take selpercatinib with or without food. But selpercatinib must be taken with a meal if you are taking medicines to reduce stomach acid. Your doctor, nurse or pharmacist can talk to you more about this.

It is important to tell your doctor, nurse or pharmacist if you are taking any other medicines before starting selpercatinib. This is because other medicines may affect how selpercatinib works. Always take selpercatinib as explained.

If you are sick just after, or miss a dose, take the next dose of selpercatinib at the scheduled time. Do not take a double dose.

Other things to remember about your capsules: 

  • Keep them in the original package and at room temperature, away from heat and direct sunlight.
  • Keep them safe and out of sight and reach of children.
  • If your treatment is stopped return any unused capsules/ tablets to the pharmacist.

About side effects

We explain the most common side effects of this treatment here. We also include some that are less common. 

You may get some of the side effects we mention, but you are unlikely to get all of them. And you may have some side effects, including rarer ones, that we have not listed here. 

Other cancer treatments may cause different side effects. If you are also having other cancer treatment, you may have other side effects.

Always tell your doctor, nurse or pharmacist about any side effects you have. They can give you: 

  • drugs to help control some side effects 
  • advice about managing side effects. 

It is important to take any drugs exactly as explained. This means they will be more likely to work for you.

Serious and life-threatening side effects

Some cancer treatments can cause serious side effects. Sometimes, these may be life-threatening. Your doctor, nurse or pharmacist can explain the risk of these side effects to you.

Contact the hospital

Your doctor, nurse or pharmacist will give you 24-hour contact numbers for the hospital. If you feel unwell or need advice, you can call at any time of the day or night. Save these numbers in your phone or keep them somewhere safe.

Common side effects

Allergic reaction

Some people have an allergic reaction while having this treatment. Signs of a reaction can include: 

  • feeling hot or flushed 
  • muscle and joint pain
  • a skin rash
  • itching
  • shivering
  • feeling dizzy
  • a headache
  • feeling breathless.

If you feel unwell or have any of these signs, tell a doctor or nurse straight away. Do not take any more of this treatment until you have spoken to them.

After checking your symptoms, your doctor may prescribe [steroids] until your symptoms are better. It is important that you take these exactly as you have been told by your doctor, nurse or pharmacist.

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:

  • nosebleeds
  • bleeding gums
  • heavy periods
  • blood in your urine (pee) or stools (poo)
  • vomit that looks like ‘coffee grounds’
  • tiny red or purple spots on your 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.

Sometimes selpercatinib may cause more serious bleeding. Contact your doctor immediately if you have any signs of bleeding.

Skin changes

This treatment can affect your skin. It may cause a rash, which may be itchy. Your doctor or nurse can tell you what to expect. If your skin feels dry, try using soap-free cleansers and unperfumed moisturising cream every day. 

Always tell your doctor or nurse about any skin changes. They can give you advice and may prescribe creams or medicines to help. Changes to your skin usually improve when treatment ends.

Dry mouth

Selpercatinib can cause a dry mouth. Sipping water regularly helps reduce the dry feeling, so carry a bottle of water with you. Eating soft, moist foods with gravy and sauces is easier than dry or chewy foods.

Tell your doctor if you have a dry mouth. They may be able to prescribe things to help.

Feeling sick

Your doctor, nurse or pharmacist will prescribe anti-sickness drugs to help prevent or control sickness. Take the drugs exactly as they tell you to, even if you do not feel sick. It is easier to prevent sickness than to treat it after it has started.

If you feel sick, take small sips of fluid often and eat small amounts regularly. It is important to drink enough fluids. If you continue to feel sick, or if you are sick (vomit) 1 to 2 times in 24 hours, contact the hospital on the 24-hour number as soon as possible. They will give you advice. They may change your anti-sickness treatment. Let them know if you still feel sick.


This treatment may cause diarrhoea. Diarrhoea means passing more stools (poo) than is normal for you, or having watery or loose stools. You may also have stomach cramps. If you have a stoma, it may be more active than usual. 

If you are passing loose stools 3 or more times a day and this is not normal for you, contact the hospital as soon as possible on the 24-hour number. Follow the advice they give you about:

  • taking anti-diarrhoea medicines 
  • drinking enough fluids to keep you hydrated and to replace lost salts and minerals
  • any changes to your diet that might help. 

They might also ask you for a specimen of your stool to check for infection.


This treatment can cause constipation. Constipation means that you are not able to pass stools (poo) as often as you normally do. It can become difficult or painful. Here are some tips that may help:

  • Drink at least 2 litres (3½ pints) of fluids each day.
  • Eat high-fibre foods, such as fruit, vegetables and wholemeal bread.
  • Do regular gentle exercise, like going for short walks.

If you have constipation, contact the hospital on the 24-hour number for advice. They can give you drugs called laxatives to help. 

If you have not been able to pass stools for over 2 days and are being sick, contact the 24-hour number straight away. 

Tummy pain

This treatment can cause pain in the tummy (abdomen). Your doctor or nurse can suggest treatments to help.

Loss of appetite

This treatment can affect your appetite. Don’t worry if you do not eat much for 1 or 2 days. But if your appetite does not come back after a few days, or if you are losing weight, tell your doctor, nurse or pharmacist. They can give you advice. They may give you food or drink supplements. Or they may suggest changes to your diet or eating habits to help.

High blood pressure

Selpercatinib can increase your blood pressure. A nurse will check your blood pressure before starting selpercatinib and regularly throughout your treatment. If you have headaches, nose bleeds or feel dizzy, let your doctor know. Your doctor can usually prescribe tablets to control high blood pressure.

If you are already on treatment for blood pressure, you will have regular blood pressure checks to make sure it stays under control. Talk to your doctor if you have any concerns.

Headache and dizziness

This treatment may cause headaches or dizziness. If this happens, let your doctor or nurse know. They can do tests to check for the cause. If a headache or dizziness is severe, contact the hospital for advice straight away.

Do not drive or operate machinery if you have dizziness.

Fluid build-up

You may gain weight, or your face, ankles and legs may swell. This improves slowly after your treatment has finished. Tell your doctor, nurse or pharmacist if you notice this side effect.

Effects on the liver and kidneys

This treatment may affect how your liver and kidneys works. This is usually mild. You will have regular blood tests to check how well your liver and kidneys are working. At the start of treatment, you will have a blood test to check your liver:

  • every 2 weeks during the first 3 months of treatment
  • once a month for the next 3 months of treatment
  • regularly thereafter.

Effects on the heart

This treatment can affect how the heart works. You will have tests to see how well your heart is working. These will be done before starting selpercatinib, after 1 week and at least every month for the first 6 months of treatment.

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
  • breathlessness
  • dizziness
  • 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.

If the treatment is causing heart problems, your doctor may need to reduce your dose of selpercatinib or ask you to stop taking it.

Feeling tired

Feeling tired is a common side effect of this treatment. It is often worse towards the end of treatment and for some weeks after it ends. Try to pace yourself and plan your day so you have time to rest. Gentle exercise, like short walks, can help you feel less tired. 

If you feel sleepy, do not drive or use machinery.

Low number of white blood cells

This treatment can reduce the number of white cells in your blood. These cells fight infection. If you have any signs of an infection, tell your doctor, nurse or pharmacist. These signs include:

  • a cough
  • a sore throat
  • diarrhoea
  • needing to pass urine (pee) often, or discomfort when you pass urine.

Contact the hospital straight away on the 24-hour number if you have any of these symptoms:

  • a temperature above 37.5°C 
  • a temperature below 36°C
  • you feel unwell, even with a normal temperature.

Other information

Blood clot risk

Cancer and some cancer treatments can increase the risk of a blood clot. Contact the hospital straight away on the 24-hour number if you have any of these symptoms during or after treatment:

  • throbbing pain or swelling in a leg or arm
  • reddening of the skin in the area – if you have black or brown skin, this can be harder to notice, but the skin might become darker
  • suddenly feeling breathless or coughing.

Always call 999 if you have:

  • chest pain
  • difficulty breathing.

A blood clot is serious, but it can be treated with drugs called anticoagulants. These thin the blood. Your doctor, nurse or pharmacist can give you more information about preventing and treating blood clots.


Doctors usually recommend that people with cancer have vaccinations for flu and for coronavirus (covid). These help reduce your risk of serious illness from these infections. Most people can have these vaccines, including people with weak immune systems.

If your immune system is weak, you should not have live vaccinations. Live vaccines can make you unwell because they contain a very weak version of the illness they will protect you against. Live vaccines include Zostavax®, which is a shingles vaccine, and the yellow fever vaccine.

It is important to ask your doctor, nurse or pharmacist for advice about having vaccinations. They can explain what vaccines are right for you and when it is best to have them.


Some cancer drugs can affect whether you can get pregnant or make someone pregnant. If you are worried about this, it is important to talk with your doctor before you start treatment.


It is possible that small amounts of chemotherapy may be passed on through vaginal fluids or semen. If you have sex during this treatment, your cancer team will usually advise using condoms or a dental dam to protect your partner.


Your doctor, nurse or pharmacist will advise you not to get pregnant or make someone pregnant while having this treatment and for some time afterwards. The drugs may harm a developing baby. It is important to use contraception to prevent pregnancy. Follow their advice about:

  • what types of contraception to use 
  • how long after treatment you should continue to use contraception. 


You are advised not to breastfeed while having this treatment, or for some time after treatment ends. This is because the drugs could be passed to the baby through breast milk. 

Your doctor, nurse or pharmacist can give you more information.

Medical and dental treatment

If you need medical treatment for any reason other than cancer, always tell the healthcare professional that you are having cancer treatment. Give them the contact details for your cancer doctor or cancer team so they can ask for advice.

If you have appointments with a dentist, always tell them you are having cancer treatment. Talk to your cancer team before you have any dental treatment.

Other medicines

Some medicines can affect how this treatment works or be harmful while you are having it. Always tell your cancer doctor, nurse or pharmacist about any drugs you are taking or planning to take, such as: 

About our information

  • Reviewers

    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.

Date reviewed

Reviewed: 01 March 2023
Next review: 01 March 2025
Trusted Information Creator - Patient Information Forum
Trusted Information Creator - Patient Information Forum

Our cancer information meets the PIF TICK quality mark.

This means it is easy to use, up-to-date and based on the latest evidence. Learn more about how we produce our information.