Local anaesthetic (LA) is a medication injected near the tooth and surrounding area to numb the nerves, so you do not feel pain during dental treatment. It is the most common way dental procedures are made comfortable.
Unlike a general anaesthetic, you remain fully awake and alert. Only the area around the tooth being treated is numbed — the rest of your body is unaffected.
What does the injection feel like?
Many people are more anxious about the injection than the dental treatment itself. Here is what to expect:
Your dentist will often apply a topical (surface) anaesthetic gel to the gum first, to reduce the sensation of the injection
You will feel a small scratch or pinch as the needle enters the gum — this lasts only a second
As the anaesthetic is injected, you may feel a slight pressure or mild stinging sensation
The area begins to feel numb within 2–5 minutes for most teeth. Lower back teeth can take up to 10 minutes to become fully numb.
The numbness typically lasts 1–4 hours depending on the type and amount of anaesthetic used
What will I feel during treatment?
Once numb, you should not feel pain during treatment. However, you may still feel:
Pressure — the sensation of something pushing or moving is carried by different nerve fibres than pain and is not blocked by local anaesthetic. This is normal.
Vibration — from the drill or instruments
Cold water — from the drill coolant spray in some cases
If at any point you feel sharp pain, raise your hand to signal the dentist. They will give you more anaesthetic before continuing.
After the anaesthetic wears off
Once the anaesthetic begins to wear off (usually 1–4 hours after the injection), some soreness is normal. The tooth, gum, and jaw area may be tender for 24–48 hours, particularly after surgical or more invasive procedures.
Take over-the-counter painkillers (ibuprofen or paracetamol) as directed if needed — ideally before the anaesthetic fully wears off
Be careful eating or drinking while numb — you cannot feel heat and may accidentally bite your cheek or lip
Avoid very hot food or drinks until sensation has fully returned
Risks and possible side effects
Local anaesthetic in dentistry has an excellent safety record and is used millions of times a year in the UK. However, rare side effects can occur:
Common:
A small bruise or soreness at the injection site — resolves within a few days
Prolonged numbness if a large volume was used
Uncommon:
A rapid heartbeat (palpitations) — some local anaesthetics contain adrenaline, which can cause a brief awareness of your heartbeat. This 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 a dental chair. Tell your dentist if you feel dizzy or unwell.
Rare:
A true allergy to local anaesthetic — genuine allergy is extremely rare. If you have been told you are allergic, inform your dentist before treatment so an alternative can be arranged.
Prolonged numbness beyond 8 hours — contact the practice if this occurs
Questions to ask your dentist
Which teeth are you numbing, and how long will the numbness last?
Can I drive after my appointment?
I am on blood pressure medication — will the adrenaline in the anaesthetic affect me?
I am anxious 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 dentist about your individual options, risks, and treatment plan. Treatment outcomes vary between patients depending on individual circumstances. Your dentist will confirm exact fees and what is suitable for your specific circumstances before you agree to any treatment.