Insulin

What is insulin?

Insulin is a hormone made by the pancreas that plays a vital role in regulating blood sugar (glucose) levels. After eating, insulin helps move glucose from the bloodstream into your body’s cells, where it can be used for energy or stored for later. People with diabetes may need insulin if their body does not make enough or cannot use it properly[1].

What is insulin used for?

Insulin is prescribed to manage high blood sugar in several forms of diabetes, particularly when the body is unable to produce or respond to insulin effectively. It is commonly used in the following situations[1]: 

• Type 1 diabetes – where the body stops producing insulin altogether 

• Type 2 diabetes – when other treatments such as tablets and lifestyle changes are not sufficient 

• Gestational diabetes – a form of diabetes that develops during pregnancy 

• Other causes of high blood sugar – such as illness or steroid use, where insulin may be needed temporarily

How does insulin work?

Insulin works by helping to lower blood glucose levels in several ways[1]: 

• It allows glucose to enter cells so it can be used for energy 

• It promotes the storage of excess glucose in the liver and muscles 

• It reduces the amount of glucose released by the liver 

There are different types of insulin, each with a different onset and duration of action[1]: 

• Rapid-acting: begins working in 10-20 minutes and lasts 2-5 hours 

• Short-acting: starts in around 30 minutes and lasts 6-8 hours 

• Intermediate-acting: starts in 1-2 hours and lasts 12-18 hours 

• Long-acting: starts in 1–2 hours and can last up to 24 hours or more

Who can take insulin?

Insulin can be used by a wide range of people, depending on their health needs and the type of diabetes they have. It may be prescribed for[1]: 

• People with type 1 diabetes, where insulin is essential for life 

• Some people with type 2 diabetes, particularly when tablets are no longer effective 

• Pregnant women with gestational diabetes who cannot manage blood sugar with diet and exercise alone 

• Individuals with temporary high blood sugar, for example due to surgery or illness 

Please tell your doctor or pharmacist about any conditions you may have or medication you take before you start treatment, and always follow the instructions in the Patient Information Leaflet[2]. 

What is the typical dosage of insulin?

Insulin dosing is highly individualised and depends on a range of factors such as body weight, diet, activity level, and how well blood sugar is controlled[1].

The dose is measured in units, and it may be taken once a day or several times a day, depending on the type. Several types of insulin may be prescribed[1]:

○ Rapid-acting: e.g. NovoRapid, Humalog

○ Short-acting: e.g. Actrapid

○ Intermediate-acting: e.g. Insulatard

○ Long-acting: e.g. Lantus, Levemir

○ Mixed insulin (a combination of types): e.g. Humulin M3

How do you take insulin?

Insulin is usually injected just under the skin, and there are a few different ways to do this depending on what is most suitable for you[1]: 

• Injection methods include: 

  ○ Pre-filled pens 

  ○ Refillable pens 

  ○ Syringes 

  ○ Insulin pumps (continuous delivery)

• Common injection sites are the abdomen, thighs, buttocks, and upper arms 

• It is important to rotate injection sites regularly to prevent skin thickening or lumps (a condition called lipodystrophy) 

Can you stop taking insulin?

Whether or not you can stop taking insulin depends on the type of diabetes you have[1]: 

• For people with type 1 diabetes, insulin is essential and must be continued for life 

• For people with type 2 diabetes, it may be possible to reduce or stop insulin if blood sugar improves through other treatments. Always speak to your doctor or pharmacist before making any changes to your insulin treatment.

What do you do if you take too much insulin?

Taking too much insulin can lead to hypoglycaemia, or low blood sugar. This can be dangerous if not treated quickly[1]. 

• Common symptoms include sweating, shaking, dizziness, hunger, and confusion 

• If this happens[1]: 

  ○ Check your blood sugar if possible. If it is below 4mmol/l or you are unable to check, treat this immediately. 

  ○ Take a fast acting carbohydrate such as a small glass of fruit juice or sugary fizzy drink, or four to five glucose tablets. You want to aim for around 15g of fast acting carbohydrate. 

  ○ Wait 10 to 15 minutes then recheck your blood sugar. If it still reads below 4mmol/l have some more fast acting carbohydrates. 

  ○ Once your blood sugar is back to normal, eat a slower acting carbohydrate such as toast or a banana. This helps keep it stable. 

  ○ If you are the person who is hypoglycaemic is unconscious, drowsy, or unable to swallow you must call 999 immediately. If prescribed and trained to use it, the glucagon injection should be administered. 

What do you do if you forget to take insulin

If you forget to take your insulin dose[1]: 

• Take it as soon as you remember, unless it’s almost time for your next scheduled dose 

• Do not take two doses at once 

• Monitor your blood sugar closely and contact your doctor or pharmacist if you are unsure what to do 

What medicines can’t you take with insulin?

Insulin can interact with other medications, so it is important to be cautious. You can usually take insulin safely with[1]: 

• Metformin 

• Statins 

• Blood pressure medicines (such as ACE inhibitors or ARBs) 

Medications that may require caution include[1]: 

• Steroids 

• Diuretics (water tablets) 

• Beta-blockers 

• Certain antidepressants 

Always inform your doctor or pharmacist about all medications and supplements you take before you start a new medicine, and follow the instructions in the Patient Information Leaflet[2]. 

What are the side effects of insulin?

Like all medicines, insulin can cause side effects. Most are mild and manageable, but some may need attention[1]. 

Common side effects include[1]: 

• Low blood sugar (hypoglycaemia) 

• Weight gain 

• Reactions at the injection site (e.g. redness, swelling, or itching) 

Less common side effects include[1]: 

• Allergic reactions 

• Lipodystrophy (lumpy or thickened skin from repeated injections in the same area) 

• Insulin resistance (where your body stops responding as well to insulin) 

You should contact your GP if you experience any of these symptoms. In rare cases, the medicine may cause severe hypos or a serious allergic reaction (anaphylaxis). You should call 999 or visit A&E immediately if you believe either of these is happening[1]. 

Symptoms of anaphylaxis include[1]:  

• Difficulty breathing  

• Tightness in throat and chest  

• Swelling of the tongue or throat  

• Feeling faint or dizzy  

• Blue/grey skin or lips  

• Loss of consciousness  

If you experience any side effects, including those not listed, you are encouraged to report them via the Yellow Card Scheme or contact your doctor, pharmacist, or nurse. This information is intended as a summary for general awareness and does not replace professional medical advice. 

The information provided in the side effects section is not a comprehensive list of all possible side effects associated with this medication. For a complete list of side effects, please refer to the Patient Information Leaflet (PIL) provided with your medication or consult your healthcare professional[2].

Frequently asked questions about insulin

Is insulin addictive? 
No. Insulin is a natural hormone and not addictive[1]. 

Can I travel with insulin? 
Yes. Keep your insulin cool (using an insulated pouch or cool bag) and carry a letter from your doctor for airport security. Ask your doctor or pharmacist about an insulin passport. This useful document allows you to make a record of your insulin type(s), dose and delivery method. It can be shown to healthcare professionals, particularly when travelling and may prevent dangerous medication errors and speeds up treatment in emergencies[1]. 

Can I drink alcohol while using insulin? 
Yes, in moderation. However, alcohol can affect blood sugar levels, so it’s important to monitor closely[1]. 

How should insulin be stored? 
Unopened insulin should be kept in the fridge. Once opened, it can usually be stored at room temperature for up to 28 days – check the instructions for your specific product[1]. It is important not to expose your insulin to high temperatures as this may prevent it from working. 

Can insulin be taken as a tablet? 
No. Insulin must be injected or delivered  subcutaneously, or injected just under the skin. Insulin is a protein and so stomach acid would break it down before it can work[1]. 

Can I exercise while taking insulin? 
Yes. Exercise is encouraged, but you should monitor your blood sugar before and after activity to avoid low levels[1]. 

Can insulin cause weight gain? 
Yes. Insulin can sometimes lead to weight gain indirectly, especially if your body is storing more calories because your blood sugar levels are more controlled[1]. 

Is insulin safe during pregnancy? 
Yes. Insulin is considered safe and is often used to treat gestational diabetes[1]. 

For the official NHS guide to insulin, visit their website.