Amoxicillin is one of the most widely prescribed antibiotics in the world, used to treat bacterial infections in the ears, lungs, sinuses, throat, skin, and urinary tract. It belongs to the penicillin family and works by stopping bacteria from building their protective cell walls, which kills them off as they try to grow and multiply.
Ear, Nose, and Sinus Infections
Middle ear infections (otitis media) are one of the most common reasons amoxicillin is prescribed, especially in children. When a child develops ear pain and fever after a cold, amoxicillin is typically the first antibiotic a pediatrician reaches for. It penetrates well into the fluid that builds up behind the eardrum, targeting the bacteria most often responsible.
Sinus infections follow a similar pattern. Most sinus infections start as viral illnesses and clear up on their own, but when symptoms last longer than 10 days or get worse after initially improving, bacteria are likely involved. Amoxicillin is the standard first-line treatment in those cases. It’s also prescribed for bacterial infections of the nose and surrounding passages that don’t resolve with time and symptom management alone.
Strep Throat and Tonsillitis
Amoxicillin is the go-to antibiotic for strep throat, an infection caused by Group A Streptococcus bacteria. The CDC recommends a 10-day course for strep, which is longer than many people expect. That full duration matters: cutting the course short increases the risk of the infection returning and, in rare cases, can lead to complications like rheumatic fever, which affects the heart.
Tonsillitis caused by bacteria (rather than a virus) is treated the same way. Most people start feeling better within two to three days of starting amoxicillin, but finishing the entire prescription is what actually clears the infection completely.
Lower Respiratory Infections
Amoxicillin treats bacterial infections in the lungs, including some forms of pneumonia and acute bacterial bronchitis. Community-acquired pneumonia, the kind you pick up in everyday life rather than in a hospital, is one of the more serious conditions it’s used for. It’s effective against many of the bacteria that commonly cause pneumonia, though more severe cases or drug-resistant bacteria may require a different antibiotic or a combination approach.
Urinary Tract and Skin Infections
Urinary tract infections (UTIs) caused by susceptible bacteria can be treated with amoxicillin, though it’s not always the first choice for UTIs. Some of the bacteria that commonly cause bladder infections have developed resistance to amoxicillin over the years, so your doctor may choose a different antibiotic depending on local resistance patterns or urine culture results.
For skin infections, amoxicillin works against certain bacteria that cause cellulitis, wound infections, and other soft tissue infections. It’s most useful when the infection is caused by bacteria known to be sensitive to penicillin-type drugs.
H. Pylori and Stomach Ulcers
Amoxicillin plays a key role in treating Helicobacter pylori, the bacterium responsible for most stomach ulcers and a significant portion of chronic gastritis. It’s never used alone for this purpose. Instead, it’s combined with other medications, typically an acid-reducing drug and one or two other antibiotics, taken together for about 14 days.
H. pylori burrows into the stomach lining where a single antibiotic can’t reliably reach it, which is why the combination approach is necessary. The acid-reducing medication changes the stomach environment to make the antibiotics more effective. Treatment regimens have evolved over the years as H. pylori has become resistant to some antibiotics, but amoxicillin remains a core part of most protocols because resistance to it is still relatively uncommon.
Preventing Infections Before Dental Work
Some people take a single dose of amoxicillin before dental procedures to prevent bacteria from the mouth entering the bloodstream and infecting the heart. This is called antibiotic prophylaxis, and it’s recommended for a specific group of patients: those with artificial heart valves, a history of infective endocarditis, certain congenital heart defects, or a heart transplant with valve problems.
The dose is taken before the procedure so the antibiotic is already circulating in the blood when bacteria are released during dental work. If the dose is accidentally missed beforehand, it can still be taken up to two hours after the procedure, according to the American Dental Association.
Why It Only Works on Bacteria
Amoxicillin has no effect on viral infections. It won’t help with the common cold, the flu, COVID-19, or most sore throats (which are viral about 70% of the time). Taking antibiotics for a viral illness doesn’t speed recovery and contributes to antibiotic resistance, which makes these drugs less effective for everyone over time.
This distinction matters because many of the conditions amoxicillin treats, like sinus infections and bronchitis, start as viral illnesses. Antibiotics only become appropriate when a bacterial infection is confirmed or strongly suspected based on symptom duration and severity.
Common Side Effects
The most frequent side effects are digestive: nausea, diarrhea, and stomach discomfort. These happen because amoxicillin doesn’t distinguish between harmful bacteria and the beneficial bacteria in your gut. Taking it with food can help reduce stomach upset.
A non-allergic rash is fairly common, especially in children. It typically appears as flat, pink spots that spread across the trunk and isn’t itchy or dangerous. This rash is particularly well-known in people who take amoxicillin while they have mononucleosis (mono), where it occurs in a large percentage of cases. A non-allergic rash doesn’t mean you’re allergic to amoxicillin, though it can be hard to tell apart from a true allergic reaction without medical evaluation.
Penicillin Allergy: Often Overreported
Because amoxicillin is a penicillin-type antibiotic, people with a documented penicillin allergy are often told to avoid it. But true penicillin allergy is far less common than people think. In studies using skin testing and controlled oral challenges, only 1.5% to 6.1% of people who reported a penicillin allergy actually tested positive. One study at a Baltimore clinic found that just 7.1% of patients who said they were allergic had an objective positive test result.
Many people are labeled as penicillin-allergic based on childhood reactions that may have been viral rashes or side effects rather than true immune-mediated allergies. Penicillin allergy also fades over time in many people. If you’ve been told you’re allergic but aren’t sure, allergy testing can clarify whether amoxicillin is safe for you. This matters because penicillin-type antibiotics are often the most effective and least expensive option for common infections, and unnecessarily avoiding them can mean getting a broader-spectrum antibiotic with more side effects.