Emergency & antidotes
Adrenaline auto-injectors
Adrenaline pens for anaphylaxis (e.g. EpiPen) — The first and most important treatment for a severe allergic reaction — given without delay into the outer thigh.
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.
Quick answer
What is Adrenaline auto-injectors?
An adrenaline auto-injector is a pre-filled, spring-loaded pen that delivers a single emergency dose of adrenaline into the thigh muscle to treat anaphylaxis — a rapid, severe allergic reaction affecting breathing, circulation or both. It is the first thing to use in that emergency.
- How it works: Adrenaline rapidly reverses the dangerous features of anaphylaxis: it opens up swollen, narrowed airways, tightens leaking blood vessels to restore blood pressure, reduces swelling, and settles the allergic release driving the reaction.
- In practice: In practice an adrenaline auto-injector is the life-saving first-line treatment for anaphylaxis (a severe, whole-body allergic reaction), and the dominant message is that it must be used early and without hesitation — delay, not the injection itself, is what costs lives.
What it is
An adrenaline auto-injector is a pre-filled, spring-loaded pen that delivers a single emergency dose of adrenaline into the thigh muscle to treat anaphylaxis — a rapid, severe allergic reaction affecting breathing, circulation or both. It is the first thing to use in that emergency.
How it works
Adrenaline rapidly reverses the dangerous features of anaphylaxis: it opens up swollen, narrowed airways, tightens leaking blood vessels to restore blood pressure, reduces swelling, and settles the allergic release driving the reaction. Because it acts within minutes on the very problems that make anaphylaxis life-threatening, giving it early is what saves lives.
In practice
In practice an adrenaline auto-injector is the life-saving first-line treatment for anaphylaxis (a severe, whole-body allergic reaction), and the dominant message is that it must be used early and without hesitation — delay, not the injection itself, is what costs lives. It is given into the outer thigh (it works through clothing), an ambulance is called straight away saying "anaphylaxis", and the person is kept lying down with their legs raised (or sat up if breathing is hard) and not stood up suddenly. A second pen is given after a short interval if there is no improvement, so people at risk carry two pens at all times and keep them in date. Because symptoms can return hours later (a biphasic reaction), everyone who has used one needs assessment in hospital even if they feel better. The practical work around these devices is training (the person and those around them — family, school, workplace — knowing how and when to use it), checking expiry and storage (not refrigerated, protected from extremes), and a personalised allergy action plan. They are extremely safe used in an emergency; common after-effects like a racing heart, shakiness and pallor are expected and pass.
Examples
Practical use
How to take it & use it well
- If someone is having a severe allergic reaction, use the pen early without hesitation, as giving it promptly is far safer than waiting to see whether things get worse.
- Press the pen firmly against the outer thigh, where it works even through clothing, and hold it in place for the few moments you have been shown before removing it.
- Call 999 straight away and say clearly that it is anaphylaxis, so the right help is sent quickly, and do this even after the pen has been used.
- Help the person lie down with their legs raised to keep blood flowing to the heart, but let them sit up if they are struggling to breathe, and never let them stand up suddenly.
- If there is no improvement after a short interval, use a second pen in the other thigh, which is why you should always carry two in-date pens with you.
- Always go to hospital even if the person seems completely better, because a second wave of the reaction can come hours later and needs to be watched for.
Common uses
- Emergency treatment of anaphylaxis
- Carried by people at risk of severe allergy (food, insect sting, drug)
- Held in schools, workplaces and first-aid settings
Monitoring
- That the person and their carers/school/workplace are trained and confident
- Pen expiry dates and correct storage (not refrigerated)
- An up-to-date personal allergy action plan and known triggers
Weighing it up
Advantages & disadvantages
Advantages
- It is the only treatment that reverses the life-threatening parts of a severe allergic reaction quickly.
- It is designed to be used by anyone, including family and bystanders, with simple training.
- It works through clothing into the outer thigh, so there is no need to undress in an emergency.
- Carrying it means people with serious allergies can get on with daily life with a vital safety net.
- Using it early greatly improves the chance of a full recovery from anaphylaxis.
Disadvantages
- It is a rescue treatment only and does not cure or prevent the underlying allergy.
- Its effect can wear off, so a single pen is sometimes not enough and a second may be needed.
- The pens have an expiry date and must be replaced, as an out-of-date pen may not work properly.
- It commonly causes a racing heart, shakiness and a pale, anxious feeling, which is expected and passes.
- Hospital assessment is still always needed afterwards, so it does not remove the need for emergency care.
Key safety principles
What to watch for
- Use it EARLY — at the first signs of a severe reaction; into the outer thigh (works through clothing). Delay is the main danger.
- Call 999 saying "anaphylaxis", keep the person lying with legs raised (or sitting up if breathing is hard), and give a second pen after a short interval if no improvement.
- Always go to hospital afterwards even if better (symptoms can return); carry two in-date pens and stay trained in their use.
Key interactions
What to avoid or check alongside
- In a true emergency the pen is always used regardless of other medicines, as the benefit far outweighs any concern.
- Some heart and blood-pressure medicines can blunt how well it works, which is one more reason a second pen and emergency help may be needed.
- Store the pens away from extremes of heat and cold, not in a fridge or a hot car, as this can spoil them.
- Check the expiry date and the liquid through the window regularly, replacing any pen that is out of date or looks discoloured.
- Keep two pens together at all times and make sure family, school or work know where they are and how to use them.
Patient & carer advice
- If in doubt during a severe reaction, use it — it is far safer to give it than to wait
- Press it firmly into the middle of the outer thigh and hold it in place; you can give it through clothes
- Carry two pens everywhere, check the dates, and always call an ambulance and go to hospital after using one
Answers
Adrenaline auto-injectors: frequently asked questions
When should I use my adrenaline auto-injector?
Use it as soon as you suspect a severe allergic reaction, such as trouble breathing, swelling of the throat or tongue, a widespread rash with faintness, or sudden collapse after a trigger. It is much safer to use it early than to wait. After using it, call 999 and say it is anaphylaxis.
Why do I need to carry two pens?
One pen is sometimes not enough, because its effect can wear off before help arrives or the reaction can be severe. If there is no improvement after a short interval, a second pen is given in the other thigh. Always carrying two in-date pens means you are covered while you wait for the ambulance.
Do I still need hospital if I feel better after using the pen?
Yes, always. A second wave of the reaction can happen hours after the first, which is why everyone who has used a pen needs to go to hospital to be watched, even if they feel completely well again. Call 999 every time the pen is used.
Will the pen work through my clothes?
Yes. The pens are designed to be pressed firmly against the outer thigh and will work through ordinary clothing, so there is no need to undress in an emergency. Avoid thick seams, pockets or anything in the way, and hold it in place for the moments you were shown.
Is it normal to feel shaky and have a racing heart afterwards?
Yes. A pounding heart, shakiness, paleness and an anxious feeling are common and expected after using the pen, and they usually pass quickly. They are not a reason to avoid using it in an emergency, as treating the allergic reaction is far more important.
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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