Rapid-acting insulin usually contains 100 units of insulin per 1ml of liquid, but some brands are also available containing 200 units of insulin per 1ml of liquid. Make sure you know what strength of insulin you're taking.
You'll usually take a dose of rapid acting insulin around 10 to 15 minutes before each meal. Your doctor or diabetes nurse will advise you on when to take it. The exact timing may depend on which brand you take. See what timing works best for you and try to stick to it as closely as possible.
Taking it before meals means that your levels of insulin are highest as your body absorbs glucose from the meal, which helps to stop your glucose level from going too high.
Your doctor or diabetes nurse will tell you how many units of insulin you'll need to take. You'll usually need to calculate your dose depending on the amount of carbohydrate food (sugar and starches) in each meal. This is known as carb counting. If you have type 1 diabetes you'll be given training in how to do this.
The dose of rapid-acting insulin you need also depends on:
As well as adjusting your dose for what you eat, you may also need to change your dose:
It's a good idea to keep a record of the amount of insulin units you inject if possible.
Testing your blood glucose regularly will help you and your diabetes healthcare team know if you're taking the right dose for you. Your doctor or diabetes nurse will explain how to do this.
Information:Most people take rapid-acting insulin using an insulin pen or a pump. The type of pen you'll use depends on which brand of insulin you've been prescribed. There are different types of pre-filled pens, reusable pens and pumps so check the instructions for the type you're using.
If you use vials and syringes to inject instead of a pen, your diabetes nurse will show you how to do this.
When you start taking insulin your diabetes nurse will show you how to use your pen to inject. Always follow the instructions for your pen.
Using an insulin pen does not usually hurt. The needles are very small as you only inject a small amount into the layer of fat just under your skin.
It's important to vary the places you inject so that you're less likely to get fatty lumps under your skin (lipohypertrophy). Although these are usually harmless, they can mean that insulin is not always absorbed at the same speed when you inject into them. This can affect your blood glucose levels.
Information:Rapid-acting insulin can also be taken using an insulin pump, which you attach to your body.
How to use an insulin pump
An insulin pump is a small device you wear all the time that delivers short acting or rapid-acting insulin throughout the day and night.
Insulin flows into your body from the pump through a tiny tube (cannula) which you insert under your skin.
Using a pump means you do not have to take injections, and you can easily adjust the dose to get the amount of insulin you need. Pumps can help to improve your blood glucose levels compared to injections. Most people find their blood glucose does not go too high or low as often.
The pump is programmed to deliver tiny amounts of insulin over 24 hours to give you the background insulin you need. This means you do not need a separate intermediate or long-acting insulin. You also use the pump controls to give a larger dose before meals.
When you start using a pump, you'll be shown how to initially programme and adjust the pump settings to change the insulin dose, and how to change the cartridge or fill the insulin reservoir in the pump, attach the infusion set to the pump, prime the pump to remove any air, and attach the infusion set to your body.
There are 2 types of pump:
Pumps are available on the NHS to:
They're not usually available on the NHS for people with type 2 or gestational diabetes.
It's important to always take the right amount of insulin. To avoid making any mistakes with your insulin dose:
Insulin pens are designed to stand up to a lot of wear and tear. But they can sometimes become faulty, and this can affect your blood glucose levels.
If you're concerned that your pen is not reliably giving the right dose of insulin, contact your doctor or diabetes nurse for advice.
If you have type 1 diabetes you'll need to take insulin for your whole life.
If you have type 2 diabetes you'll need to take insulin if other treatments for diabetes are not reducing your blood glucose enough. Once you start taking insulin it's likely that you'll need to take it for the rest of your life, provided it improves your blood glucose and you cope well with the treatment.
If you're taking insulin to treat gestational diabetes you can usually stop taking it once your baby is born, as the condition usually goes away after you give birth.
It's important to take insulin as recommended by your doctor or nurse. Speak to them if you have any problems with taking it.
When your blood glucose is well managed you're less likely to get the short-term symptoms of high blood glucose (hyperglycaemia) such as blurred vision, needing to pee more, tiredness and feeling very thirsty. You're also less likely to get serious long-term problems that can damage your heart, kidneys, eyes, nerves and feet.
Stopping insulin suddenly can lead to severe hyperglycaemia and a life-threatening condition called diabetic ketoacidosis.
If you have any concerns about your insulin treatment, talk to your diabetes specialist, doctor or diabetes nurse.
Taking too little insulin increases the risk of high blood sugar (hyperglycaemia) and long-term complications from diabetes.
If you forget to take your rapid-acting insulin before a meal, and you've already eaten, consider taking a slightly smaller dose or correction dose, or contact your doctor or diabetes nurse for advice.
Look out for any signs of high or low blood glucose levels, and check your blood glucose levels more often than usual. Contact your doctor or diabetes nurse if you're concerned.
Never take 2 doses to make up for a forgotten dose.
Taking too much insulin can make your blood sugar go too low, causing hypoglycaemia (a hypo). You might also have a hypo if you:
Symptoms of low blood sugar include:
It's also possible for your blood sugar to go too low while you're asleep. If this happens, you may wake up at night feeling sweaty and confused, or you may feel tired or have a headache in the morning. Speak to your diabetes team if you think you might be having hypos at night.
These symptoms happen when your blood glucose falls below 4 mmol/L.
If you get hypo symptoms, follow the instructions you've been given to treat a hypo:
Always carry glucose tablets or high sugar snacks with you in case you have a hypo.
Do not drive, cycle or use machinery if you've taken too much insulin, even if you do not have symptoms. If you have a hypo, do not drive for at least 45 minutes after you've recovered.
Try to make sure someone stays with you if you've taken too much insulin.
If you have very low blood glucose (a severe hypo) you may become drowsy or unconscious. Make sure your family or friends know what to do if this happens, including how to give a glucagon injection, and when to call 999 for an ambulance.
Find out more about side effects of rapid-acting insulin including severe hypos.
Page last reviewed: 6 July 2023
Next review due: 6 July 2026