Understanding Dental Local Anaesthetic
A calm guide to how the numbing injection (local anaesthetic) works at the dentist, what it feels like, and what is normal afterwards.
Urgent help: who to contact
Call 999 straight away if your lips, mouth, throat or tongue suddenly swell, or you are struggling to breathe or swallow, after a numbing injection — this could be a very rare but severe allergic reaction (anaphylaxis).
What is local anaesthetic?
Local anaesthetic (LA) is a medicine injected near the tooth and the area around it. It numbs the nerves so you do not feel pain during dental treatment. It is the most common way to make dental treatment comfortable.
It is not like a general anaesthetic. You stay fully awake and alert. Only the area around the tooth being treated goes numb. The rest of your body is not affected.
What does the injection feel like?
Many people worry more about the injection than the treatment itself. Here is what to expect:
- Your dental team will often put a numbing gel (topical anaesthetic) on the gum first. This makes the injection feel less sharp.
- You will feel a small scratch or pinch as the needle goes into the gum. This lasts only a second.
- As the medicine goes in, you may feel slight pressure or mild stinging.
- For most teeth, the area starts to feel numb within 2–5 minutes. Lower back teeth can take up to 10 minutes to go fully numb.
- The numbness usually lasts 1–4 hours. This depends on the type and amount of medicine used.
What will I feel during treatment?
Once you are numb, you should not feel pain during treatment. But you may still feel:
- Pressure. The feeling of pushing or moving travels along different nerve fibres from pain. Local anaesthetic does not block it. This is normal.
- Shaking (vibration) from the drill or tools
- Cold water from the drill's cooling spray, in some cases
If you feel sharp pain at any point, raise your hand to tell the dentist. They will give you more anaesthetic before carrying on.
After the anaesthetic wears off
As the numbness starts to wear off (usually 1–4 hours after the injection), some soreness is normal. The tooth, gum and jaw may be tender for 24–48 hours. This is more likely after surgery or bigger treatments.
- If you need painkillers, take ones you can buy in a shop (ibuprofen or paracetamol) as directed. It is best to take them before the numbness fully wears off.
- Adults: follow the dose on the packet. Children: use children's paracetamol or ibuprofen and give the dose on the packet for their age. Check with a pharmacist, dentist or doctor before you take ibuprofen if you have asthma, have had a stomach ulcer, have heart, kidney or liver problems, take blood-thinning medicines, or are pregnant.
- Take care eating or drinking while you are numb. You cannot feel heat, and you may bite your cheek or lip by accident.
- Children: watch them until the numbness wears off. They may bite, chew or suck their numb lip, cheek or tongue without noticing. This can cause a painful sore. Do not give them food or chewing gum until normal feeling has returned.
- Avoid very hot food or drinks until feeling has fully come back.
Risks and possible side effects
Local anaesthetic at the dentist has an excellent safety record. It is used millions of times a year in the UK. But rare side effects can happen:
Common:
- A small bruise or soreness where the needle went in. This goes within a few days.
- Numbness that lasts longer than usual if a large amount was used
Uncommon:
- A fast heartbeat (palpitations). Some local anaesthetics contain adrenaline. This can make you aware of your heartbeat for a short time. It is harmless and settles within a minute or two.
- Feeling faint. Anxiety, rather than the anaesthetic itself, is the most common cause of fainting in the dental chair. Tell your dental team if you feel dizzy or unwell.
Rare:
- A true allergy to local anaesthetic. A real allergy is extremely rare. If you have been told you are allergic, tell your dental team before treatment. They can then arrange another option.
- Nerve injury. Very rarely, an injection to numb the lower teeth can bruise or injure a nerve. This can cause numbness, tingling or a change in taste in the lip, chin or tongue. It can last for weeks or months. In very rare cases it is permanent.
- Numbness that has not worn off after 6 hours. Contact the practice if this happens.
Questions to ask your dental team
- Which teeth are you numbing, and how long will the numbness last?
- Can I drive after my appointment?
- I take blood pressure medicine. Will the adrenaline in the anaesthetic affect me?
- I am nervous about injections. What can you do to make this as comfortable as possible?
This leaflet is for general information only and does not replace professional dental advice. It is intended to support — not replace — the discussion with your dental team about your individual options, risks, and treatment plan. Treatment outcomes vary between patients depending on individual circumstances. Your dental team will confirm exact fees and what is suitable for your specific circumstances before you agree to any treatment.
Sources
- Local anaesthetic. NHS website (nhs.uk), reviewed December 2025.
- Drug Prescribing for Dentistry, 3rd edition; online version updated for BNF 91. Scottish Dental Clinical Effectiveness Programme (SDCEP), 2016, updated 2026.
Links checked 18 October 2026.
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