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Introduction

Bowel preparation medicine, which is a laxative, needs to be taken before procedures such as colonoscopy, flexible sigmoidoscopy or CT colonography to cleanse and empty the bowel. You will already have received a separate leaflet entitled Having a Colonoscopy or Flexible Sigmoidoscopy, which describes the procedure itself.

To get a clear view of the lining of your bowel, it must be as empty and as clean as possible. To achieve this, you will need to follow a low fibre diet for 2 days and take the laxatives included in your pack according to the timetable beginning on page 2. The laxatives will give you watery diarrhoea so you must drink adequate fluids and stay close to a toilet.

Check that you have been sent 10 tablets of sennosides and 2 sachets of Citramag. If not, please contact the Endoscopy unit at Wexham Park on 0300 615 4157 or Frimley Park on 0300 613 6647. For comfort whilst preparing your bowel, you may wish to put some ointment on your bottom. Zinc and castor oil, Sudocrem and Vaseline are all suitable and may be purchased from a chemist. 

Special precautions

  • If you are taking oral anticoagulants (warfarin, apixaban, dabigatran, rivaroxaban) or antiplatelet drugs (clopidogrel, ticagrelor) and other blood thinning medications, please DO NOT stop them unless we have advised you to do so.
  • If you are on warfarin, please have your INR checked 7 days before your procedure and call us on the contact number below (depending on which hospital your procedure is booked) with the result, so that we can instruct you on what to do.
  • If you do not hear from us 7 days before your procedure, kindly give us a call at Endoscopy unit:
  • If you are asthmatic, please bring your inhalers with you and let the nurse know.
  • If you are taking any regular medication for diabetes, please refer to a separate leaflet available by telephoning Wexham Park on 0300 615 4157 or Frimley Park on 0300 613 6647. It explains how to control your blood sugar around the time of your procedure as it is important to maintain a blood sugar above 5 mmol/l. Check your blood sugar level and if necessary suck some glucose tablets ahead of your procedure to achieve this. Please bring your diabetic pills or insulin with you to your appointment.
  • If you have a colostomy (external stool bag on a stoma from previous bowel surgery), the bowel preparation medicine will work in the same way. You are advised to put on a drainable appliance before taking the laxatives until after the examination. 
  • Aspirin in low doses is allowed. In the 7 days leading up to the procedure, do not take more than 75mg of aspirin per day.
  • If you are taking oral contraception, please note that increased bowel transit caused by the laxatives may lead to loss of the pill before it has been absorbed. It is advisable to take alternative measures to avoid pregnancy in the week following your procedure.
  • If you are taking any other regular medications please continue these are normal.
  • Please let us know if you are pregnant or trying to conceive.

Seven days before your examination

Stop taking iron tablets. 

Four days before your examination


Stop taking any constipating agents, e.g., co-phenotrope, codeine phosphate etc but continue with other medication and any laxatives. Avoid fibre supplements such as Fybogel.

Two days before your examination

Eat only the following low-fibre foods: white fish, chicken, cheese, white bread, eggs, butter or margarine, plain yoghurt, honey (but not jam or marmalade), rich tea biscuits, potato (without the skin), yellow jelly (not red), ice cream, sorbets (not red). Have plenty to drink. Do not eat high-fibre foods, red meat, pink fish, fruit, vegetables, mushrooms, salad, wholemeal bread, cereals or pulses in any form.

The day before your examination

Have a good breakfast and a light lunch, eating foods from yesterday’s permitted list. After this, do not eat any solid food until after your examination but drink plenty of clear fluids (tea, coffee, squash, non-alcoholic drinks, carbonated drinks, water, clear soups, Bovril, Oxo, etc). You may have small amounts of milk in tea and coffee. Clear jelly (yellow only) and ice cream are permitted. If your admission time is at or after 2.00 pm tomorrow, you may have a light evening meal today from the list of permitted foods.

Citramag preparation

To prepare a sachet of Citramag, dissolve the contents in 200mls (8 fluid ounces) of hot water in a large measuring jug. Pour the water in slowly whilst mixing to avoid excessive fizzing which could cause the fluid to spill and be lost. Allow it to cool before drinking. 

For appointments before 2.00 pm

At 6.00 pm on the day before your procedure, in the comfort of your home, take all 10 tablets of sennosides with a glass of water. At 7.00 pm prepare one sachet of Citramag. When it has cooled, drink it slowly over an hour then drink 1 litre of clear fluids (e.g. consommé, squash, water). Have no solid food. You should expect frequent bowel movements and diarrhoea to start within 2 hours of the laxatives. Some intestinal cramping is normal. This is just the beginning of the clear-out process. Have an early night if possible.

On the morning of your procedure, at around 5.30 am, prepare and drink the second sachet of Citramag in the same way followed by 1 litre of clear fluid. You should continue to have light drinks (water, squash, black tea), stopping 2 hours before your appointment time.

For appointments at or after 2.00 pm

On the morning of your procedure, in the comfort of your home, take all 10 sennosides tablets at 7 am or earlier. At 7:30 am prepare one sachet of Citramag. When it has cooled, drink it slowly over an hour then drink 1 litre of clear fluids (e.g., consommé, squash, water). Have no solid food. You should expect frequent bowel movements and diarrhoea to start within 2 hours of the laxative. Some intestinal cramping is normal. This is just the beginning of the clear-out process.
At 9:30 am, prepare and drink the second sachet of Citramag in the same way followed by 1 litre of light drinks (water, squash, black tea). You should continue to have light drinks, stopping 2 hours before your appointment time.

Further laxative information

It is advisable that you stay near a toilet once you have started taking the laxatives. The timings of the laxatives are designed so that the effects wear off before you are due to leave home and travel to the hospital. You may have some bloating or stomach cramps – this is normal.

Remember to keep drinking clear fluids to stop you from becoming dehydrated. As a guide, try to drink about one glass every hour. Signs that you are dehydrated include dizziness, headache and confusion.

If you vomit at any stage after taking the bowel preparation solution, or if you have any concerns regarding this preparation, please contact Endoscopy unit: (within office hours, 8.00am – 5.00pm) Wexham Park hospital on 0300 615 4163, Frimley Park hospital on 0300 613 6045 or Heatherwood hospital on 0300 614 4020.

Please report any allergic reactions to the preparation such as rash, itchiness, or redness to the Endoscopy unit or your GP. In very rare cases you may have a reaction that causes swelling of the face, lips, tongue or throat. If this happens seek medical help as soon as possible.

Contact us

If you have any queries relating to this information, please contact the Endoscopy service.

About this information

Service:
Endoscopy

Reference:
H/030

Approval date:
22 April 2024

Review date:
1 April 2026

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Important note 

This page provides general information only. It is developed by clinical staff and is reviewed regularly every 3 years for accuracy. For personal advice about your health, or if you have any concerns, please speak to your doctor.