Insulin is a hormone that is made by cells called beta cells. These are part of little islands of cells (islets) within the pancreas. Hormones are chemicals that are released into the bloodstream and work on various parts of the body. Insulin helps to control the levels of glucose (sugar) in your blood.

When your blood glucose level begins to rise (after you eat), the level of insulin should also rise. Insulin works on the cells of your body and makes them take in glucose from the bloodstream. Some of the glucose is used by the cells for energy, and some is converted into glycogen or fat (which are stores of energy).

When is insulin prescribed?

Your doctor may prescribe insulin if you have a condition called diabetes. This is when your body does not make enough insulin to meet its needs, or if it does, not use the insulin it makes effectively. There are two different types of diabetes:

Type 1 diabetes is the type of diabetes that typically develops in children and young adults. In type 1 diabetes the body stops making insulin and the blood glucose level goes very high. Treatment to control the blood glucose level is with insulin injections and a healthy diet.

Type 2 diabetes is the type which occurs mainly in people aged over 40. The first-line treatment is diet, weight control and physical activity. If the blood glucose level remains high despite these measures then tablets to reduce the blood glucose level are usually advised. Insulin injections are needed in some cases.

How is insulin given?

Insulins are given by injection under the skin (sometimes called subcutaneous injection); this is because insulin cannot be taken by mouth, as it is destroyed by the digestive juices in your digestive system. They are available as vials to be injected with a separate syringe, as a cartridge to be used with an injection device (pen), or in pre-filled injection devices. Insulins can also be given continuously by a pump.

Your doctor or diabetes nurse will show you how to inject yourself with insulin. It is usually injected under the skin into your upper arms, thigh, buttocks or abdomen. Most people take 2-4 injections of insulin each day. The type and amount of insulin you need may also vary each day, depending on what you eat and the amount of exercise you do.

It is important to remember that insulin doses are referred to in terms of units. Make sure you know how much to use - ask your doctor or nurse if you are unsure.

What types of insulins are available to be prescribed?

  1. Rapid-acting analogue: can be injected just before, with or after food. It tends to last between 2 and 5 hours and only lasts long enough for the meal at which it is taken.
  2. Long-acting analogue: is usually injected once a day to provide background insulin lasting approximately 24 hours.
  3. Short-acting insulin: should be injected 15-30 minutes before a meal, to cover the rise in blood glucose levels that occurs after eating. It has a peak action of 2-6 hours and can last for up to 8 hours.
  4. Medium-acting and long-acting insulin: are taken once or twice a day to provide background insulin or in combination with short-acting insulins/rapid-acting analogues. Their peak activity is between 4 and 12 hours and can last up to 30 hours.
  5. Mixed insulin: is a combination of medium-acting and short-acting insulin.

Which insulin is usually prescribed?

The type of insulin or device that you are prescribed will be tailored to your needs. It may consist of one or more types of insulin and the amounts you use will be carefully chosen to suit you.

What is hypoglycaemia?

Hypoglycaemia (which is often called a 'hypo') occurs when the level of glucose becomes too low, usually under 60 mg%. People with diabetes who take insulin are at risk of having a hypo. A hypo may occur if you have taken too much insulin, delayed or missed a meal or snack, or have taken part in unplanned exercise or physical activity.

Symptoms of hypoglycaemia include: trembling, sweating, anxiety, blurred vision, tingling lips, paleness, mood change, vagueness or confusion. To treat hypoglycaemia you should take a sugary drink or some sweets. Then eat a starchy snack such as a sandwich.

Do I need any special monitoring or tests?

You will usually need to monitor your blood glucose levels at home. You will also need to have a special blood test called HbA1c every few months.

Blood glucose monitoring

It is likely you will need to monitor your glucose levels by using a monitor at home. This is to make sure that your insulin is working. Your doctor or diabetes clinic will provide you with a blood glucose monitor, test strips and a lancing device. A lancing device makes a very small cut in the skin so you can place a small drop of blood on the test strip.


This test measures a part of the red blood cells. Glucose in the blood attaches to part of the red blood cells. This part can be measured and gives a good indication of your blood glucose control over the previous 1-3 months. This test is usually done regularly by your doctor or nurse. Ideally, the aim is to maintain your HbA1c to less than 6.5% but this may not always be possible to achieve and the target level of HbA1c should be agreed on an individual basis between you and your doctor.

What are the side-effects?

Apart from hypo (described earlier), insulin has very few side-effects. Lipodystrophy (lumpiness at the site of the injection) has been reported. To help avoid this happening, try varying the places you inject.

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