Amoxicillin: what it treats, how to take it, side effects
Last updated September 3, 2026.
Amoxicillin is a penicillin-like antibiotic used to treat infections caused by bacteria. It works by stopping the growth of bacteria. It does not work for colds, the flu, or other viral infections, and taking it when it is not needed makes future infections harder to treat.
What does it treat?
Amoxicillin treats certain bacterial infections, including infections of the ear, nose, throat, skin, urinary tract, and lower respiratory tract such as pneumonia. It is also combined with other medications (clarithromycin and lansoprazole) to eliminate H. pylori, the bacteria behind many stomach ulcers. MedlinePlus notes it is sometimes used for Lyme disease and for anthrax exposure. Because it only works on bacteria, a clinician decides whether your infection is the kind it can treat.
How do you take it?
Amoxicillin comes as a capsule, tablet, chewable tablet, and liquid suspension. It is usually taken every 8 or 12 hours, at the same times each day, and it can be taken with food to prevent stomach upset. For strep infections, the label recommends at least 10 days of treatment to prevent complications like rheumatic fever. Shake the liquid well and measure it with a dosing syringe or marked medicine spoon, not a kitchen spoon. Finish the entire prescription even if you feel better, because stopping early can let the infection come back stronger. If you miss a dose, take it when you remember unless it is almost time for the next one; never take a double dose.
Side effects to know
- Common: nausea, vomiting, and diarrhea. Temporary yellow, brown, or gray tooth discoloration can happen (mostly in children) and usually comes off with brushing or dental cleaning.
- Serious: rash, itching, or hives; blistering or peeling skin; wheezing, trouble breathing or swallowing, or swelling of the face, throat, tongue, or lips; and severe watery or bloody diarrhea, which can start up to 2 months or more after treatment ends. Stop taking it and get medical help right away if any of these appear.
Who should not take it?
Anyone who has had a serious allergic reaction (such as anaphylaxis or Stevens-Johnson syndrome) to amoxicillin or to another beta-lactam antibiotic like penicillin or a cephalosporin should not take it. Tell your clinician if you have mononucleosis, kidney or liver disease, asthma, hay fever, or hives, and if you are pregnant, planning pregnancy, or breastfeeding. Amoxicillin can make hormonal birth control less effective, so use a backup method while taking it. Taking allopurinol at the same time raises the chance of a rash.
When is it an emergency?
Call 911 for signs of anaphylaxis: trouble breathing or swallowing, swelling of the face, throat, tongue, or lips, or hives spreading quickly. Stop the medication and call your doctor immediately for a blistering or peeling rash or for severe, watery, or bloody diarrhea. For an overdose, call Poison Control at 1-800-222-1222. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper.
What a Pymander AI doctor consult looks like
Illustrative example, not a real member's messages.
Common questions
How long does amoxicillin take to work?
Most people start to feel better during the first few days of treatment, according to MedlinePlus. If your symptoms are not improving or are getting worse after that, call your doctor - the bacteria may be resistant or the diagnosis may need a second look.
Can I drink alcohol while taking amoxicillin?
Neither the DailyMed label nor MedlinePlus lists alcohol as a known interaction with amoxicillin. That said, alcohol can worsen nausea and slow your recovery from an infection, so many clinicians suggest skipping it until you are well. Ask your doctor what makes sense for you.
Should I take amoxicillin with food?
You can. Amoxicillin works with or without food, but MedlinePlus notes it may be taken with food to prevent stomach upset, which is the most common complaint with this antibiotic.
What should I do if I miss a dose?
Take the missed dose as soon as you remember it. If it is almost time for your next dose, skip the missed one and go back to your regular schedule. Do not take two doses at once to catch up.
Does amoxicillin affect birth control?
It can. MedlinePlus cautions that amoxicillin may decrease the effectiveness of hormonal contraceptives (pills, patches, rings, and injections), so you should use another method of contraception while taking it and talk to your doctor about backup options.
Why do I have to finish the whole course if I feel better?
Feeling better does not mean the bacteria are gone. Stopping amoxicillin too soon or skipping doses can leave the infection only partly treated and can help the bacteria become resistant to antibiotics, making them harder to kill next time.