By Carolien Koreneff, Credentialled Diabetes Educator, Registered Nurse

Most people will have a hospital admission at some point in their lives. When you have diabetes the risk of needing a hospital admission increases, as you are at increased risk of complications from diabetes. At any time, about 25% of people admitted to hospital in Australia also have diabetes.

The most common procedures in hospital, that can impact your blood glucose levels, are endoscopies. Endoscopies are a type of investigation that allows a doctor to take a look at you on the inside, literally.

Preparing for an endoscopy

Doctors can take a look at your digestive tract on a colour TV monitor, by using an endoscope; a special camera, attached to a flexible tube with a light on it. The camera can be inserted through your mouth and throat into the oesophagus and stomach; this is called a gastroscopy. Or a similar camera can be inserted through the rectum, up through the colon and into the small intestines; this is called a sigmoidoscopy or colonoscopy.

These procedures are not particularly comfortable, but you usually will not experience any discomfort, as you will be asleep for the most part. Although not officially considered an operation, you will be given a sedative, or anaesthetic. This means that you have to fast before the procedure and, as a result, your diabetes medications may need adjustment.

Why would you need an endoscopy?

Endoscopies are a way for the doctor to determine what the cause may be for stomach or abdominal pain, to check if you have any ulcers, to find out if there is any bleeding or if you have any tumours. During the colonoscopy the doctor may take a small sample, a biopsy, which can be checked in the laboratory. They can also remove polyps from the bowels (and thereby prevent them from turning into cancer), and they can stop small bleeds.

Overall endoscopies are safe. However, in some cases people may get a reaction to the anaesthetic, and others may have some bleeding or an infection could develop afterwards. It is important to talk to the doctor before the procedure about the risks and what can be done to prevent problems or deal with any issues that arise.

Preparation

Gastroscopy

If you are having a gastroscopy then usually the only preparation required is to fast before the procedure. If the gastroscopy takes place in the morning, you are generally not allowed to eat or drink anything from around 10pm the night before. If the gastroscopy is planned for the afternoon you may be allowed to have a light breakfast early in the morning, but you will have to fast from then on, until you are fully awake from the anaesthetic.

Colonoscopy

If you are having a colonoscopy you will also have to fast, but in addition you will need to undergo a bowel cleanse. This means that two days before the procedure you are only allowed to have soft foods. Grainy products such as wholegrain breads, pasta and brown rice, foods high in fibre, such as a lot of vegetables, fruits, seeds and nuts have to be avoided. These are the things your doctor or educator usually recommend you eat to keep your blood glucose levels more stable. This means that a soft diet is generally higher in glycaemic index, which may mean result in higher blood glucose levels.

The day before the procedure you are only allowed to have clear fluids such as lemonade, apple juice, jelly, tea or coffee without milk, water (including sparkling water) and clear soups or broth. Mostly you would have the sugar-free version of these items, like sugar-free jelly, Sprite Zero or Diet 7-Up. But there is a risk of developing hypoglycaemia (low blood glucose level) because you are not having any “real” food the day before a colonoscopy. If your blood glucose level drops the sugary version or these products will help to remedy the hypo. Your doctor will give you a list of the things you can and can’t have, as well as instructions on to what to do with your medications, or in case of a hypo.

The day before the procedure, usually sometime in the afternoon, you will have to drink a special preparation to clean your bowels. This may be a slightly uncomfortable step (it doesn’t taste great and will make you go to the toilet a lot), but it is a very important one. Your bowels need to be clean so the doctor can see things more clearly. Your doctor will give you instructions as to how, why and when to start the preparation but, once you do, you will want to be near a bathroom!

Medications

Insulin

If you are having a gastroscopy or a colonoscopy, insulin doses have to be reduced. Rapid-acting insulins (Novorapid, Humalog, Apidra or Fiasp) may need to be stopped and in some cases the pre-mixed insulins (Mixtard, Novomix, Humalog Mix25, Humalog Mix50, Ryzodeg) will need to be reduced significantly. Even longer-acting insulins like Optisulin, Toujeo or Levemir may need to be reduced. If you were to take your usual insulin doses on your preparation day you would be at serious risk of a bad hypo.

Metformin

Even some tablet medications for diabetes may need to be reduced or temporarily stopped when preparing for, or undergoing, an endoscopy. For example, many doctors prefer you not to have Metformin (Diabex, Diaformin, Formet) for 24-48 hours before the procedure, as these medications could, although rarely, cause lactic acidosis – a build-up of lactic acid in your muscles.

Sulphonyureas

Sulphonyureas, medications that stimulate your pancreas to make more insulin, can also increase the risk of hypos. The most common sulphonylurea is gliclazide (also known as Diamicron or Glyade), another is glimepiride (Amaryl), and there is also glibenclamide (Daonil, although this is not used all that often anymore).

SGLT-2 inhibitors

SGLT-2 inhibitors (empagliflozin or dapagliflozin, brand names: Jardiance, Forxiga or combination treatments Xigduo or Jardiamet) lower your blood glucose level by letting some of the glucose pass through your kidneys into the bladder. People who take this type of medications are at a slightly higher risk of dehydration and there is a small risk of developing diabetic ketoacidosis (DKA), this is a medical emergency. In DKA increased levels of acid in the blood can cause organs such as the kidneys and the liver to fail when certain types of anaesthetic are given, so these medications usually have to be stopped for a day or two prior to the procedure.

GLP-1 antagonists and GLP-1/GIP receptor agonists

Medications such as Ozempic and Trulicity are GLP-1 antagonists. GLP-1/GIP receptor agonists are a combination medication that include GLP-1, as described above, and another component; GIP. An example of this is Mounjaro.

These types of medication cause food to stay in your stomach for longer, giving your pancreas more time to make the insulin needed and reduce hunger. As these medications cause delayed gastric emptying, they can potentially increase the risk of aspiration if you are being sedated. Aspiration can happen when food, liquid, saliva, or other substances accidentally enter the airway (windpipe) instead of the oesophagus (food pipe), potentially reaching the lungs and increasing the risk of pneumonia. Your doctor may recommend additional preparation before a gastroscopy, such as a day or two of clear fluids, or may recommend that you stop the GLP-1 containing medication a few weeks before the procedure. The Australian Therapeutic Goods Administration (TGA) issued an alert on 3 June 2025 regarding potential risks associated with this group of medicines.  

Delayed gastric emptying can also impact the quality of bowel preparation for colonoscopies. Hence, GLP-1 containing medications may need to be ceased a few weeks before a colonoscopy, or you may need additional preparation to make sure that your bowels are clean enough.

However, stopping the medication may negatively affect your glucose levels and/or may delay urgent surgery. High glucose levels can increase your length of stay and increase the risk of infection and other complications. It is therefore crucial to always discuss all medications you take, including any non-prescription or over-the-counter medications, with all doctors and specialists.

Personalised advice

Your doctor or credentialled diabetes educator will give you personalised advice as to what you should do with your medicines and if, or how much, insulin is needed. It is important to follow medical advice and not make treatment decisions without discussing this with your doctor first.

After the procedure

The procedure usually takes only 20-30 minutes, and you will be kept in the recovery ward under observation for a few hours or until you are awake and able to eat and drink normally. You will resume your normal diabetes treatment from this time.

If your doctor does not give you any advice on when to restart your medications, make sure you ask.

Tips

• Bring your diabetes medication with you to take after the procedure
• Tell the medical staff you have diabetes as soon as you arrive
• Do not take a double dose of medicines you’ve missed
• Do not panic if your blood glucose levels are a little higher after the procedure, they should start to come down within a few hours or over in the following day or two
• If you start to feel unwell once you get home, call your GP or contact your local hospital but don’t stop taking your usual medication

Plan

Write down your medication plan for the two days before the procedure, for the procedure day, and the day after your procedure. Sedation can affect your thinking, so it may be helpful to have something in writing to refer to.