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Teysuno (pronounced tay-sun-oh) is a chemotherapy drug made up of the following drugs:

  • tegafur – the body changes tegafur into a common chemotherapy drug called fluorouracil
  • gimeracil – this makes tegafur last longer in the body so you need a lower dose
  • oteracil – this protects normal cells and so reduces the side effects

You might have it as a treatment for advanced stomach cancer. You usually have it in combination with another chemotherapy drug called cisplatin.

How teysuno works

Teysuno is one of a group of chemotherapy drugs known as the anti metabolites. These stop cells making and repairing DNA. Cancer cells need to make and repair DNA in order to grow and multiply.

How you have teysuno

Teysuno is a capsule. You take the capsules twice a day, morning and evening. Swallow them whole with plenty of water. You should take the capsules either an hour before eating or an hour after eating.  

Taking your capsules

You must take capsules according to the instructions your doctor or pharmacist gives you.

You should take the right dose, not more or less.

Never stop taking a cancer drug without talking to your specialist first.

When you have teysuno

You take teysuno twice a day for 21 days (3 weeks). You then don’t take it for a week. This is one cycle of treatment. Then your next cycle of treatment starts. 

You usually take teysuno together with another chemotherapy drug called cisplatin. You have teysuno and cisplatin for 6 cycles of treatment. Cisplatin is then stopped and you continue taking teysuno for as long as it works. 


You have blood tests before and during your treatment. They check your levels of blood cells and other substances in the blood. They also check how well your liver and kidneys are working.

Side effects

We haven't listed all the side effects. It is very unlikely that you will have all of these side effects, but you might have some of them at the same time.

How often and how severe the side effects are can vary from person to person. They also depend on what other treatment you are having. For example, your side effects could be worse if you are also having other drugs or radiotherapy.

When to contact your team

Your doctor, nurse or pharmacist will go through the possible side effects. They will monitor you closely during treatment and check how you are at your appointments. Contact your advice line as soon as possible if:

  • you have severe side effects 
  • your side effects aren’t getting any better
  • your side effects are getting worse

Early treatment can help manage side effects better. 

Contact your doctor or nurse immediately if you have signs of infection, including a temperature above 37.5C or below 36C.

Common side effects

Each of these effects happens in more than 1 in 10 people (10%). You might have one or more of them. They include:

Risk of infection

Increased risk of getting an infection is due to a drop in white blood cells. Symptoms include a change in temperature, aching muscles, headaches, feeling cold and shivery and generally unwell. You might have other symptoms depending on where the infection is.

Infections can sometimes be life threatening. You should contact your advice line urgently if you think you have an infection. 


You might be breathless and look pale due to a drop in red blood cells. This is called anaemia.

Bruising and bleeding

This is due to a drop in the number of platelets in your blood. These blood cells help the blood to clot when we cut ourselves. You may have nosebleeds or bleeding gums after brushing your teeth. Or you may have lots of tiny red spots or bruises on your arms or legs (known as petechia).

Feeling or being sick

Feeling or being sick is usually well controlled with anti sickness medicines. Avoiding fatty or fried foods, eating small meals and snacks, drinking plenty of water, and relaxation techniques, can all help.


Tiredness and weakness (fatigue) can happen during and after treatment - doing gentle exercises each day can keep your energy up. Don't push yourself, rest when you start to feel tired and ask others for help.

Diarrhoea or constipation

Tell your doctor or nurse if you have diarrhoea or constipation. They can give you medicine to help. 

Loss of appetite

You might lose your appetite for various reasons when you are having cancer treatment. Sickness, taste changes or tiredness can put you off food and drinks.

Numbness or tingling in fingers and toes

Numbness or tingling in fingers or toes is often temporary and can improve after you finish treatment.

Occasional side effects

Each of these effects happens in more than 1 in 100 people (1%). You might have one or more of them.

  • eye problems such as watery eyes and redness (conjunctivitis)
  • headaches and dizziness
  • high temperature and chills
  • hearing loss
  • muscle pain
  • difficulty sleeping
  • weight loss
  • sore and dry mouth
  • soreness, redness and peeling on palms and soles of the feet
  • skin problems such as rash, dry skin and itching
  • indigestion or heartburn
  • kidney changes that are usually mild and unlikely to cause symptoms
  • high or low blood pressure
  • swelling of your ankles and legs due to a build up of fluid (oedema)
  • loss of taste
  • lung problems such as breathlessness and cough
  • hair loss
  • liver changes that are very mild and unlikely to cause symptoms
  • tummy (abdominal) pain
  • difficulty swallowing

Rare side effects

Each of these effects happens in fewer than 1 in 100 people (1%). You might have one or more of them. They include:

  • mood changes such as feeling very sad and depressed
  • changes to the heart muscle that are usually temporary
  • blood clots
  • a stroke
  • a hole (or split) in the bowel wall
  • sore, tender and swollen breasts
  • difficulty getting an erection (impotence)

Coping with side effects

We have more information about side effects and tips on how to cope with them.

Important information

Other medicines, foods and drink

Cancer drugs can interact with some other medicines and herbal products. Tell your doctor or pharmacist about any medicines you are taking. This includes vitamins, herbal supplements and over the counter remedies.

Pregnancy and contraception

This drug may harm a baby developing in the womb. It is important not to become pregnant or father a child while you are having treatment with this drug and for at least 6 months afterwards. Talk to your doctor or nurse about effective contraception before starting treatment.


It is unknown whether this treatment affects fertility in people. Talk to your doctor before starting treatment if you think you may want to have a baby in the future.


Don’t breastfeed during this treatment because the drug may come through into your breast milk.

Treatment for other conditions

Always tell other doctors, nurses, pharmacists or dentists that you’re having this treatment if you need treatment for anything else, including teeth problems.


Don’t have immunisations with live vaccines while you’re having treatment and for up to 12 months afterwards. The length of time depends on the treatment you are having. Ask your doctor or pharmacist how long you should avoid live vaccinations.

In the UK, live vaccines include rubella, mumps, measles, BCG, yellow fever and the shingles vaccine (Zostavax).

You can:

  • have other vaccines, but they might not give you as much protection as usual
  • have the flu vaccine (as an injection)
  • be in contact with other people who have had live vaccines as injections

Avoid close contact with people who have recently had live vaccines taken by mouth (oral vaccines) such as oral polio or the typhoid vaccine.

This also includes the rotavirus vaccine given to babies. The virus is in the baby’s poo for up to 2 weeks and could make you ill. So avoid changing their nappies for 2 weeks after their vaccination if possible. Or wear disposable gloves and wash your hands well afterwards.

You should also avoid close contact with children who have had the flu vaccine nasal spray if your immune system is severely weakened. 

More information about this treatment

For further information about this treatment go to the electronic Medicines Compendium (eMC) website.

You can report any side effect you have to the Medicines Health and Regulatory Authority (MHRA) as part of their Yellow Card Scheme.

Last reviewed: 
03 Sep 2018
  • Electronic Medicines Compendium

    Accessed April 2018

  • Immunisation against infectious disease: Chapter 6: General contraindications to vaccination
    Public Health England
    First published: March 2013 and regularly updated on the Gov.UK website

  • Oral Systemic AntiCancer Therapies (SACT) Counselling Handbook for Pharmacy and Nursing staff

    London Cancer Alliance (LCA) West and South, 2015

  • Multicenter Phase III Comparison of Cisplatin/S-1 With Cisplatin/Infusional Fluorouracil in Advanced Gastric or Gastroesophageal Adenocarcinoma Study: The FLAGS Trial
    J Ajani and others
    Journal of Clinical Oncology, 2010. Vol 28, Number 9, Pages 1547-1553 

  • Fluorouracil versus combination of irinotecan plus cisplatin versus S-1 in metastatic gastric cancer: a randomised phase 3 study
    N Boku and others
    The Lancet, 2009. Vol 10, Number 11, Pages 1063-1069 

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