A penicillin antibiotic
Amoxicillin
A widely used penicillin antibiotic for many common bacterial infections — not for colds and other viral illnesses, and not for anyone allergic to penicillin.
What is Amoxicillin?
Amoxicillin is a penicillin antibiotic and one of the most commonly prescribed in the UK. It treats a broad range of bacterial infections, including some chest, ear, sinus, throat, dental and urinary infections.
Education and reference only. This is a plain-language guide to Amoxicillin — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Amoxicillin is one of the most commonly prescribed antibiotics in the UK. It is a penicillin and is used for a broad range of bacterial infections — chest infections, ear infections, dental infections, sinus and throat infections, and some urine infections — as well as in specific combinations to treat stomach-ulcer bacteria (Helicobacter pylori). It is taken as a short course, just long enough to clear the infection. Like all antibiotics, it works only against bacteria, so it does nothing for colds, flu or most sore throats, which are usually caused by viruses.
How it works
Amoxicillin attacks the cell wall that bacteria need to hold themselves together. By stopping the bacteria from building and repairing this wall, the medicine causes them to break apart and die, which lets the body clear the infection. Because it acts on a structure that human cells do not have, it targets bacteria while leaving the body's own cells alone. It is well absorbed when swallowed, so it can be taken with or without food.
Company & origin
Originated / developed by: Beecham Research Laboratories (now GSK).
Amoxicillin is a broad-spectrum semisynthetic penicillin discovered by scientists at Beecham Research Laboratories in the UK around 1972. It was marketed under the brand Amoxil; Beecham later became part of GlaxoSmithKline (GSK).
Practical use
How to take Amoxicillin
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Take the full course exactly as prescribed, even if you feel better before it is finished, to clear the infection and reduce resistance.
- Can be taken with or without food, spaced as evenly as you can through the day.
- If you miss a dose, take it as soon as you remember, then space the next doses out; do not double up.
- Tell your prescriber if you have ever had a penicillin allergy before taking it.
- Report a rash, wheezing, facial swelling or breathing difficulty straight away, and persistent or severe diarrhoea during or after the course.
Weighing it up
Advantages & disadvantages of Amoxicillin
Advantages
- Effective against a wide range of common bacterial infections.
- Well established with a long safety record, including use in children and pregnancy where appropriate.
- Usually well tolerated by people who are not penicillin-allergic.
- Can be taken with or without food, which is convenient.
Disadvantages
- Must not be used by people with a true penicillin allergy, in whom it can cause serious reactions.
- Can cause nausea, diarrhoea and thrush.
- Like all antibiotics, overuse contributes to antibiotic resistance.
- May rarely trigger Clostridioides difficile diarrhoea, which needs prompt attention.
Practical use
Good to know
Amoxicillin is taken as a short, defined course — and it is important to take it exactly as prescribed and to finish the course as advised, rather than stopping early when you feel better. Using antibiotics only when truly needed, and completing the agreed course, is part of antimicrobial stewardship — using these medicines carefully so they keep working for everyone and to slow the rise of resistant bacteria. The single most important safety point is allergy: anyone who has had a reaction to penicillin should not take amoxicillin. It can be taken with or without food, and loose stools are a common, usually mild, side effect.
Who should not take it / use with caution
- Anyone allergic to penicillin or to any penicillin antibiotic — this is the key safety rule, and a clear penicillin allergy means amoxicillin must be avoided.
- People who have had a severe allergic reaction (such as swelling, breathing difficulty or anaphylaxis) to any beta-lactam antibiotic need an alternative and should make sure this is recorded.
- Used with care in people with glandular fever (infectious mononucleosis), where it commonly causes a widespread rash, and the dose is adjusted in significant kidney impairment.
Monitoring
- Whether the infection is improving as expected
- For any sign of allergy (rash, swelling, breathing problems)
- For persistent diarrhoea after a course; kidney function where relevant
Side effects
- Loose stools or mild diarrhoea, feeling sick, or an upset stomach — common and usually settle.
- Thrush (a fungal overgrowth) in the mouth or vagina, as the antibiotic can disturb the body's normal balance of microbes.
- A rash, which can sometimes signal allergy — and rarely a serious allergic reaction with swelling of the face or throat, wheeze or collapse, which is a medical emergency (call 999). Persistent or severe watery diarrhoea after antibiotics should also be reported.
Key interactions
- It can occasionally enhance the effect of warfarin, so anticoagulant monitoring may be needed during and after a course.
- Methotrexate levels can rise when taken alongside penicillins, which needs care.
- Some other antibiotics and certain other medicines interact; always tell your pharmacist what else you take, including anything bought over the counter.
Available as: Capsules, tablets and an oral suspension (liquid) for those who cannot swallow capsules; also given by injection in hospital.
Answers
Amoxicillin: frequently asked questions
Can I take amoxicillin if I am allergic to penicillin?
No. Amoxicillin is a penicillin, so anyone with a penicillin allergy should not take it and needs a different antibiotic. Make sure any penicillin allergy is clearly recorded on your records and mention it whenever an antibiotic is prescribed.
Why do I need to finish the whole course?
You should take amoxicillin exactly as prescribed and finish the course as advised. Stopping early — even if you feel better — can leave some bacteria behind and is part of how resistance develops. If you have side effects or think you no longer need it, speak to your prescriber or pharmacist rather than simply stopping.
Will amoxicillin help my cold or sore throat?
Usually not. Colds, flu and most sore throats are caused by viruses, and antibiotics do not work against viruses. Taking an antibiotic when it is not needed gives you the side effects without the benefit and helps resistance to spread. Your prescriber will judge whether an infection is bacterial and likely to benefit.
It is giving me diarrhoea — is that normal?
Mild loose stools are common with amoxicillin and usually settle. Keep well hydrated. However, severe, watery or bloody diarrhoea, or diarrhoea that comes on after the course, should be reported promptly, as antibiotics can occasionally upset the gut more seriously.
What is the difference between amoxicillin and Amoxil?
They are the same medicine — amoxicillin is the generic (active-ingredient) name and Amoxil is a brand name. Generic amoxicillin contains the identical active ingredient.
The wider class
About Penicillins
Amoxicillin belongs to the penicillins class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.
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Authoritative sources
- BNF: Amoxicillin.
- electronic Medicines Compendium (SmPC): Amoxicillin.
- NICE CKS: Amoxicillin.
- NICE: Antimicrobial stewardship.
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