Bowel preparation: the options and how to make it easier

Use the instructions for your own appointment

Your instructions should say which product to collect, how to mix it, how much to drink, what else to drink, and when to stop food and fluids. Glycoprep products and combination kits are not all the same. Use the exact product and dilution on your instruction sheet.

Our team checks whether constipation, a previous poorly prepared colon, kidney or heart problems, diabetes, a fluid restriction or medicines could affect your preparation. Some people need a longer preparation plan or extra laxatives prescribed beforehand. Please do not add them yourself.

Booked for flexible sigmoidoscopy? Read about enema preparation for the lower bowel. →

A low-residue diet usually comes first

For a short period before the preparation, your service will usually ask you to choose foods that leave less material in the bowel. This generally means lower-fibre choices such as white bread, rice or pasta, eggs, fish or chicken, while avoiding wholegrains, nuts, seeds and other high-fibre foods as instructed.

Some people are also asked to take bisacodyl (an additional laxative to stimulate bowel cleansing) as part of the preparation plan. Only take it if it is included in the instructions for your own appointment.

Standard Glycoprep

Glycoprep contains macrogol (polyethylene glycol or PEG) with salts. It holds water in the bowel to wash out the contents. It is effective, but the volume and taste can cause fullness or nausea.

PEG-based preparations can be useful when limiting changes in body salts. The product and fluid plan still need to suit your health.

Why 3, 4 or sometimes 6 litres?

Standard Glycoprep courses commonly use 3 or 4 litres. A larger or extended course, sometimes 6 litres, may be prescribed for marked constipation or a previous poor clean-out. More is not automatically better: the diet, timing and completing the course matter too.

The preparation drink and total fluid intake are different. Lower-volume products still need extra clear fluids. Follow your own product, sachet count and mixing instructions; do not reduce the water or increase the dose yourself.

What other preparations are available?

I usually start with Glycoprep. If a lower-volume alternative is appropriate, I generally prefer Plenvu. Moviprep, PicoPrep and combination kits are other options for selected people, but each has different fluid and safety considerations. Contact us before buying or switching products.

Why is the preparation sometimes split into two doses?

Often, part is taken the day before and the rest on the day of colonoscopy. This is called split dosing and generally cleans the bowel better than finishing everything the day before. Some afternoon appointments use a same-day plan.

The timing needs to fit your appointment, travel and fasting requirements. Follow the schedule we send you, including the final time for drinking.

If nausea makes it hard to drink

If nausea was a problem before, ask our team about anti-nausea medicine before preparation day. A short pause or slower drinking may help mild nausea or fullness, while keeping your schedule and drinking cut-off. Call the team if you keep vomiting or cannot keep fluids down.

Practical ways to make preparation easier

• Read the instructions several days ahead and collect everything you need. Plan a quiet evening near a toilet.
• Mix each sachet with the exact amount of water instructed, then chill it if the product allows. A straw can make the taste easier. Do not concentrate the mixture to reduce the volume.
• Drink at the pace on your instruction sheet. Smaller regular amounts may be easier than trying to drink a large amount at once.
• Use a variety of the clear fluids allowed in your plan, such as clear broth, pulp-free apple juice or an allowed electrolyte drink, as well as water. Avoid red or purple drinks. Milk and smoothies are not clear fluids. If you have diabetes or a fluid restriction, follow your individual plan.
• A short walk may help bloating. Avoid fizzy drinks if they make this worse.
• Apply a little barrier cream, such as petroleum jelly, around your bottom before frequent bowel motions start. Soft toilet paper or gentle washing can reduce soreness.

How do I know if the preparation is working?

Aim for watery bowel motions you can see through, without solid pieces. Finish the prescribed course even if the output clears early, unless the team tells you to stop. Keep the drinking cut-off and do not add laxatives yourself.

What if the preparation is not clear enough?

Call the endoscopy service on your appointment letter if you cannot finish, keep vomiting, have little or no bowel output, or still pass thick brown liquid or solids after the prescribed course. Contact the service before it closes if you are already struggling.

If you are unsure whether the preparation is adequate and cannot reach anyone, for example with an early-morning appointment, attend at the booked time and tell the team. They will assess whether the examination can proceed or whether additional preparation, such as an enema or further bowel-cleansing medicine, can be provided if time allows.

If you feel unwell, seek medical advice rather than waiting for the appointment. Severe or increasing tummy pain, a swollen tummy with vomiting, fainting or confusion need urgent assessment. In an emergency call 111.

Contact us if preparation is difficult

If you would like to discuss an alternative regimen, contact our team before preparation day. Tell us which product you previously used, what was difficult, and whether your last colonoscopy preparation was satisfactory. We can consider a different product, timing or anti-nausea treatment.

Check regular medicines and fluid instructions

Let our team know about blood thinners, diabetes or weight-loss medicines, iron and any fluid restriction prescribed for another health condition, such as heart or kidney disease.

Your plan should state whether each medicine needs to be withheld and when to restart it if withheld. Some medicines can be continued. Call if any instructions are missing or unclear.

Related information

• Food, fluids and regular medicines before endoscopy
• About colonoscopy
• Propofol versus conscious sedation
• Your endoscopy journey