Pain
Local anaesthetics
Numbing medicines (e.g. lidocaine) — Numb a specific area for procedures and pain — safe within limits, with dose ceilings that matter.
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 Local anaesthetics?
Local anaesthetics temporarily numb a specific part of the body so a procedure can be done painlessly or an area of pain can be relieved, without affecting consciousness. They are given as injections, creams, sprays and patches.
- How it works: They block the sodium channels that nerves use to send signals, so pain messages from the treated area cannot reach the brain and the area goes numb.
- In practice: In practice local anaesthetics numb a defined area for stitches, dental work, minor surgery, joint injections and procedures, and are used as creams, sprays, injections and patches (for some nerve pain).
What it is
Local anaesthetics temporarily numb a specific part of the body so a procedure can be done painlessly or an area of pain can be relieved, without affecting consciousness. They are given as injections, creams, sprays and patches.
How it works
They block the sodium channels that nerves use to send signals, so pain messages from the treated area cannot reach the brain and the area goes numb. The same channel-blocking action on the heart and brain is what causes toxicity if too much reaches the bloodstream — which is why the total dose is capped.
In practice
In practice local anaesthetics numb a defined area for stitches, dental work, minor surgery, joint injections and procedures, and are used as creams, sprays, injections and patches (for some nerve pain). The dominant safety theme is the maximum dose: because absorption into the bloodstream causes local-anaesthetic systemic toxicity — tingling around the mouth, a metallic taste, ringing in the ears, then potentially seizures and dangerous heart effects — the total amount is carefully limited by body weight, and emergency treatment (lipid emulsion) is kept available where larger amounts are used. Some are combined with adrenaline to make them last longer and reduce bleeding, but adrenaline-containing solutions are avoided in fingers, toes and other end-arteries. Topical preparations are useful before needles in children but have their own absorption limits, especially over broken skin or large areas. People are warned that the area stays numb for a while, to protect it from heat and injury, and clinicians always check for allergy and inject carefully to avoid going into a vessel.
Examples
Practical use
How to take it & use it well
- For a procedure, the anaesthetic is usually injected or applied to a small area by a trained professional, who will check it has fully numbed the area before starting.
- Tell the person treating you about any heart conditions, liver problems, allergies or all the medicines you take, as these affect how the anaesthetic is used and how much is safe.
- After the area is numb, take care not to bite your lip, cheek or tongue, or to burn or injure the numb skin, as you will not feel pain to warn you until the effect wears off.
- Some products contain adrenaline to make the numbing last longer and reduce bleeding, but these are never used on fingers, toes, the nose, ears or the penis, where they could cut off the blood supply.
- Numbing creams and sprays bought for minor uses should be applied only to the area and amount stated, as applying too much over broken or large areas can lead to too much being absorbed.
- Stay until you are told it is safe to leave after a procedure, and follow any aftercare advice as the numbness gradually fades.
Common uses
- Numbing for stitches, dental and minor surgery
- Numbing skin before needles (topical)
- Some nerve-related pain (lidocaine patches)
Monitoring
- Adequacy of numbing and the total dose used
- Early signs of systemic toxicity during larger procedures
- The numb area afterwards (protect from burns/injury)
Weighing it up
Advantages & disadvantages
Advantages
- They allow many procedures, from dental work to stitches and minor surgery, to be done painlessly while you stay awake.
- They numb only the area treated, avoiding the risks of being put fully to sleep.
- They work quickly and their effect wears off in a predictable way.
- Adding adrenaline to some preparations makes the numbing last longer and reduces bleeding during a procedure.
- Numbing creams and sprays can take the sting out of needles, minor procedures and some skin discomfort.
Disadvantages
- If too much enters the bloodstream, it can cause serious effects on the heart and brain, so the amount is carefully limited.
- The numb area cannot feel pain, so there is a risk of accidentally biting or burning it before sensation returns.
- Some people can have allergic reactions, though true allergy is uncommon.
- Preparations containing adrenaline must never be used on fingers, toes or other end areas.
- Numbness, tingling or clumsiness can persist for a while after a procedure until the effect fully wears off.
Key safety principles
What to watch for
- There is a maximum dose by body weight — exceeding it risks local-anaesthetic systemic toxicity (mouth tingling, metallic taste, seizures, heart effects).
- Adrenaline-containing solutions are avoided in fingers, toes and other end-artery sites.
- Numbness persists after the procedure — protect the area from heat and injury; always check for allergy.
Key interactions
What to avoid or check alongside
- Other medicines that affect the heart's rhythm can add to the heart effects if too much anaesthetic reaches the bloodstream.
- The adrenaline in some preparations can interact with certain antidepressants and beta-blockers, affecting blood pressure and heart rate.
- Using several numbing products at once, or over large or broken areas, increases how much is absorbed and the risk of toxicity.
- Liver problems can slow how the anaesthetic is cleared, so less may be needed, which the professional will take into account.
- Always tell the person treating you about all your medicines and any heart or liver conditions before a procedure.
Patient & carer advice
- The area will stay numb for a while — take care with hot drinks and avoid biting a numb lip or cheek
- Tell us about any previous reaction to local anaesthetic or dental injections
- Report dizziness, tingling around the mouth, ringing in the ears or a racing heart during treatment
Answers
Local anaesthetics: frequently asked questions
What are the signs that a local anaesthetic has affected my whole body?
If too much enters the bloodstream, early signs can include a numb or tingling mouth, a metallic taste, ringing in the ears, dizziness or feeling odd, which can progress to confusion, fits or heart problems. Tell the person treating you immediately if you feel any of these during or after an injection.
Why isn't adrenaline used to numb my finger or toe?
Adrenaline narrows blood vessels, which is helpful in most areas but dangerous in fingers, toes, the nose, ears and the penis, where it could cut off the blood supply. For these areas, an anaesthetic without adrenaline is used instead.
How long will I stay numb after a procedure?
Numbness usually wears off gradually over a few hours, depending on the anaesthetic used and whether it contained adrenaline. While the area is numb, take care not to bite, scratch or burn it, as you will not feel the warning of pain.
Can I be allergic to local anaesthetic?
True allergy to local anaesthetics is uncommon, and many reactions people report are actually to other ingredients or to anxiety. If you think you have reacted before, tell the person treating you so they can choose carefully and watch you closely.
Is it safe to use numbing cream at home?
Numbing creams and sprays are fine for minor uses if you apply only the amount stated to the area stated. Applying too much, or using it over large or broken areas of skin, can let too much be absorbed, so always follow the instructions.
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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