Endocrine / Diabetes
Insulin
The essential hormone replacement for type 1 diabetes and advanced type 2 diabetes.
Education and reference only. This is a plain-language class overview — it deliberately contains no doses. Always check the current Summary of Product Characteristics (SmPC), the BNF and your local formulary before prescribing or administering any medicine.
What it is
Insulin is used in everyone with type 1 diabetes and in many people with type 2 diabetes when other treatments are not enough. It comes in several types that differ in how quickly they act and how long they last, allowing regimens to be tailored to the person.
How it works
Injected insulin replaces or supplements the body's own insulin, moving glucose from the blood into cells and switching off the liver's glucose output. Matching the type and timing of insulin to meals and activity is the key to good, safe control.
In practice
In practice insulin safety is about systems and education: never confuse units with millilitres, use the right device, and teach every patient to recognise and treat a hypo. Requirements shift with illness, activity, alcohol and steroids, so regimens need review rather than "set and forget". In type 1 diabetes insulin must never be stopped — even when not eating — because of the risk of ketoacidosis.
Examples
Practical use
How to take it & use it well
- Inject it into the fatty layer just under the skin, usually in the tummy, thighs or upper arms, and rotate the spot each time to avoid lumps.
- Match the timing to the type you use; some are taken with meals and others once or twice a day, so follow your specific plan.
- Store unopened insulin in the fridge and keep the pen or vial you are using at room temperature, away from heat and direct sunlight.
- Check your blood sugar as advised and always carry a fast-acting sugar source in case of a hypo (low blood sugar).
- Never share pens or needles, and dispose of needles safely in a sharps bin.
- If you miss or are unsure about a dose, do not simply guess or double up; follow your sick-day or missed-dose plan or contact your diabetes team.
Common uses
- Type 1 diabetes
- Type 2 diabetes not controlled on other agents
- Diabetes in pregnancy
- Acute management (e.g. DKA — specialist setting)
Monitoring
- Blood glucose (self-monitoring and/or continuous monitoring)
- HbA1c
- Injection sites for lipohypertrophy
- Episodes of hypoglycaemia
Weighing it up
Advantages & disadvantages
Advantages
- It directly and effectively lowers blood sugar and can be adjusted to your needs.
- It is essential and life-saving for people with type 1 diabetes.
- It can be used when other diabetes medicines are no longer enough.
- Different types allow flexible plans to match meals and daily routine.
- It can be used safely in pregnancy to control diabetes.
Disadvantages
- It can cause low blood sugar (hypos), which can be serious if not treated promptly.
- It is given by injection, which some people find inconvenient or difficult at first.
- It often leads to some weight gain.
- It requires blood sugar monitoring and careful timing around meals and activity.
- Injecting in the same spot repeatedly can cause skin lumps that affect absorption.
Key safety principles
What to watch for
- Hypoglycaemia is the main risk — recognise and treat it promptly.
- Insulin errors are a major source of harm: never confuse units with millilitres, and never use the wrong device or strength.
- Requirements change with illness, activity, alcohol and other medicines such as steroids.
Key interactions
What to avoid or check alongside
- Alcohol can cause delayed low blood sugar, sometimes hours later, so eat with it and monitor carefully.
- Other diabetes medicines can add to the blood-sugar-lowering effect and increase hypo risk.
- Steroids raise blood sugar and may mean your insulin needs adjusting.
- Beta-blockers can mask the early warning signs of a hypo, such as a racing heart.
- Illness, vomiting and reduced eating can change your insulin needs and require a sick-day plan.
- Strenuous exercise lowers blood sugar and may need extra carbohydrate or dose changes.
Patient & carer advice
- Learn to recognise and treat a "hypo" and carry fast-acting sugar
- Rotate injection sites
- Have a "sick day" plan — do not stop insulin in type 1 diabetes even if not eating
Use with
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Answers
Insulin: frequently asked questions
What is a hypo and what do I do?
A hypo is low blood sugar, causing shakiness, sweating, confusion or hunger. Treat it quickly with fast-acting sugar such as glucose tablets or a sugary drink, then a snack, and check your level.
Where should I inject it?
Into the fatty layer under the skin of the tummy, thighs, buttocks or upper arms. Rotate the site each time to prevent lumps that can affect how the insulin works.
How do I store it?
Keep spare insulin in the fridge but not frozen. The pen or vial in use can stay at room temperature for a limited time, away from heat and sunlight. Check the leaflet for details.
Can I drink alcohol?
In moderation and with food, yes, but alcohol can cause low blood sugar that may come on hours later, so monitor your levels and avoid drinking on an empty stomach.
Is it safe in pregnancy?
Yes. Insulin is the usual treatment for diabetes in pregnancy because it controls blood sugar well and does not cross to the baby in a harmful way. Your team will guide your doses.
Authoritative sources
Always verify against the source
This overview is for orientation. For doses, interactions, contra-indications and the full monograph, use:
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