Amoxicillin Side Effects You Should Know About

Amoxicillin Side Effects – Overview

Amoxicillin is a penicillin-class antibiotic available in the U.S. since 1974. The difference between amoxicillin and penicillin is that amoxicillin is more effective against more and different types of bacteria. After that, doctors have prescribed amoxicillin to treat infections in different parts of the human body: ear, nose, throat, genitourinary tract, skin, and lower respiratory tract. (1)

Those infections caused by β-lactamase–negative bacteria (Streptococcus species, Staphylococcus spp., Haemophilus influenza, Proteus mirabilis, or Enterococcus faecalis) can be effectively treated only with amoxicillin. The antibiotic can also be used in combination with other medications, for instance, clarithromycin and lansoprazole, for the treatment of Helicobacter pylori infection. (1)

Although well-established and effective, amoxicillin may cause diarrhea, nausea, and vomiting, usually manageable at home. In rare cases, this antibiotic may cause an allergic reaction or other side effects that need immediate medical care. (1)

This article is all about the amoxicillin side effects. Keep reading to discover the mild conditions you can manage and when to call your doctor. Also, learn how to take amoxicillin properly and prevent it from becoming resistant.

Amoxicillin’s common side effects

The most common adverse reactions in patients treated with amoxicillin (>1%) are rash and gastrointestinal symptoms: diarrhea, nausea, and vomiting. (1)

Amoxicillin Side Effects

Amoxicillin Side Effects – Common side effects

Skin rash

Skin rash is a common penicillin antibiotic side effect. It can appear in 5-10% of children taking amoxicillin. If it is an allergic rash, it will appear a few hours after the first dose. (2)

The non-allergic rash appears a few days after the patient takes amoxicillin and disappears after a couple of days, up to 6 days, often when the treatment is completed. This skin rash looks like small pink spots that appear on the chest, stomach, or back. (2)

Skin rash can be misdiagnosed as an allergic reaction to amoxicillin; therefore, consult your doctor even if it looks like a non-allergic rash, especially if it happens to your kid. Don’t stop taking the medication without consulting your doctor. (1-2)


Trillions of microorganisms such as bacteria, viruses, fungi, and parasites live in our healthy bodies and make the so-called microbiome. Many of these bugs are helpful and stimulate the immune system, break down toxic food, and synthesize specific vitamins and amino acids. Yet, some of those bugs can be harmful; in healthy individuals, both bugs coexist in balance. (3)

Using antibiotics like amoxicillin kills not only the bacteria that cause the infection but also helpful bacteria living in the bowels. As a result, harmful bacteria may become overnumbered and may cause diarrhea. (3)

In many patients that use antibiotics, diarrhea lasts for a few days. However, it is essential to keep your body hydrated, so drink plenty of water and electrolyte solutions. Talk to your doctor if you have diarrhea; the doctor may recommend you take probiotics. Be aware that in some cases, when the bacteria Clostridium difficile causes diarrhea, it would need specific medical care, as described later in this article in more detail.

You can get probiotic supplements in pills containing live active bacteria, ready to use. Another option is a diet, food rich with fibers that feed beneficial microbiota in the body. Garlic, onion, asparagus, leeks, bananas, fruits, beans, and whole grains are good sources of prebiotic fibers. (3)

Nausea and vomiting

Nausea is feeling sick to your stomach and feeling the urge to vomit. Vomiting is when you force the content in the stomach up through the esophagus (food pipe) and out from the mouth to through up. Amoxicillin may cause these symptoms, as do other conditions, such as food poisoning, migraine headaches, or severe pain due to kidney problems. (4)

Vomiting can make you dehydrated, so you should get enough fluids. It may cause trouble keeping the liquid, so drink small amounts frequently. While having these symptoms avoid spicy, fatty, or salty food with a strong smell that can irritate your stomach; instead, eat bland or boiled food. Talk to your doctor, who may recommend a medication that can treat nausea and vomiting. (4-5)

Rash, diarrhea, nausea, vomiting, and changes in taste or headache can be severe or don’t go away. If this happens to you, you should tell your doctor. Your doctor may decide to reduce the dose, recommend dietary changes, or change the antibiotic.

Other Amoxicillin side effects

Some other side effects that patients reported when taking amoxicillin are:

  • Mucocutaneous candidiasis – is an infection caused by Candida fungi present in the mouth, gastrointestinal tract, and vagina. It appears like white or yellow plaques similar to a rash. This infection happens due to the change in the native bacteria in our body; (1, 6)
  • A liver dysfunction (including elevated liver enzymes), including cholestatic jaundice, hepatic cholestasis, and acute cytolytic hepatitis; (1)
  • Having crystals in the urine (crystalluria) due to too many crystals can cause stones which may produce a blockage, developing a kidney condition called acute kidney injury. It may happen when amoxicillin has overdosed; (1, 7)
  • Changes in the blood such as:
    • anemia – not enough red blood cells to transport oxygen in the body; (1, 8)
    • thrombocytopenia – a condition when the number of platelets in the blood is too low; (1, 9)
    • eosinophilia – increased number of eosinophils (a type of white blood cell) in the body; (1, 10) or
    • agranulocytosis – the body doesn’t make enough white blood cells. (1, 11)
  • Reversible hyperactivity, anxiety, insomnia, confusion, convulsions, behavioral changes, and dizziness; (1)
  • Tooth discoloration (brown, yellow, or gray staining) in pediatric patients. Often tooth discoloration can be reduced or eliminated with brushing or dental cleaning. (1)

You may find the whole list of side effects in the amoxicillin Patient Information sheet (1). You should read it carefully.

Serious side effects

Some side effects can be rare but serious such as:

  • Allergic rash;
  • Skin blisters or peeling;
  • Itching;
  • Hives;
  • Wheezing;
  • Difficulty swallowing or breathing;
  • Swelling of the face, throat, tongue, lips, and eyes;
  • Watery or bloody stools (severe diarrhea) that may occur with or without fever and stomach cramps. (1, 12)

If you experience any of the above side effects, you should stop taking amoxicillin and call your doctor or 911 to get emergency medical treatment.

Warnings and precautions

You should be aware of the following conditions and act accordingly. (1)

Anaphylactic Reactions

Patients with amoxicillin therapy, hypersensitive to penicillin, reported serious and occasionally fatal reactions. Anaphylaxis can be demonstrated with breathing problems, wheezing, rash, and swelling of the lips, face, or tongue. Signs of anaphylaxis require immediate medical attention.

This anaphylaxis occurs in patients taking amoxicillin orally but more frequently follows the parenteral therapy. Tell your doctor if you have had a hypersensitive reaction to penicillin, cephalosporin, or other allergens. (1)

Clostridium Difficile Associated Diarrhea

Clostridium difficile-associated diarrhea (CDAD) may occur when using nearly all antibacterial agents, including amoxicillin. Due to antibacterial treatment, C. difficile overgrowth and the normal flora become imbalanced. C. difficile produces toxins that cause CDAD, from mild diarrhea to fatal colitis. (1)

CDAD occurs over two months after the antibiotic was taken and can be refractory to antimicrobial therapy. In such a case, you will need a doctor’s consultation for diagnosis and medical treatment, including in the hospital. Fluid and electrolytes, protein supplementation, an antibiotic treatment appropriate for C. difficile, and surgical evaluation are usually recommended. (1) Most patients are given fixaxomicin for initial or recurrent infections. Those with severe infections are treated with oral vancomycin.

Other warnings and precautions

Another warning is related to patients with mononucleosis, where a high percentage of them develop an erythematous skin rash. Therefore, those patients should not take amoxicillin. (1)

The presence of phenylalanine amino acid in the tablets is another precocious measure (e.g., each Amoxil 200 mg chewable tablet contains 1.82 mg of phenylalanine). (1) In people with phenylketonuria, there is a lack or a reduced amount of the enzyme that breaks down phenylalanine. High phenylalanine levels may cause serious health problems that lead to intellectual disability. (13)

Amoxil suspension is an alternative for individuals with phenylketonuria because the suspension does not contain phenylalanine. (1)

Antibiotic resistance

Amoxicillin is a well-established antibiotic often used as first-line treatment of many infections caused by Streptococcus species, Haemophilus influenzae, or Salmonella spp. (1, 14) It works in a way that disrupts the synthesis of bacterial cell wall binding to proteins inside the bacterial cell walls. This binding results in bacterial lysis and death. (15)

Still, some bacteria, such as Escherichia coli, produce the enzyme ß-lactamase that inactivates ß-lactam antibiotics. This enzyme hydrolyzes the ß-lactam ring in the antibiotic structure. After that, bacteria become resistant to this group of antibiotics. (15)

Over the years, E.colli, the major cause of urinary tract infections (UTI), has developed resistance to amoxicillin. That is why the Infectious Diseases Society of America, American Family Physicians, and the American Urological Association do not recommend amoxicillin as a first-line treatment for UTIs. (16-18)

Some reasons for developing antibiotic resistance include taking antibiotics when not needed, missing antibiotic doses, stopping treatment earlier, or using inappropriate antibiotics. Antibiotic resistance has become a global problem because a limited number of antibiotics are still effective in fighting bacterial infections. Some infections, if untreated, can lead to severe and life-threatening conditions such as pneumonia or sepsis. (19)

Therefore, you should take amoxicillin and other antibiotics as prescribed. (1)

Recommended dosage

Amoxicillin is available in the form of capsules (250 mg and 500 mg), tablets (500 mg), and powder for oral suspension (125 mg/5 mL, 200 mg/5 mL, 250 mg/5 mL, and 400 mg/5 mL). (1)

Your doctor will recommend the dose strength and the duration of the treatment depending on the type of bacteria that caused the infection and the infection severity, which can last from a couple of days to several weeks.

The recommended daily dose in adults is 750 to 1750 mg/day, divided into 2 or 3 doses every 8 or 12 hours. In children three months or older, the recommended daily dose varies from 20 to 45 mg/kg/day, divided into 2 or 3 doses. (1)

The purpose of antibiotics usage is to kill bacteria completely. Therefore, the treatment should continue as your doctor prescribed, although feeling better a few days after beginning the treatment. (1)

Take away

Amoxicillin is an established antibiotic with proven efficacy. Its side effects are well-known and mostly transitory and manageable. However, in rare cases of symptoms associated with an allergic reaction or severe diarrhea, don’t wait but call your doctor immediately.

Call your doctor if you experience a serious side effect or have unusual problems. You or your doctor may report side effects to the Food and Drug Administration’s (FDA) MedWatch Adverse Event Reporting program online ( or by phone (1-800-332-1088). (12)

When using amoxicillin as long as prescribed, it will keep it effective against bacteria. Keeping this broad-spectrum antibiotic as a long-term effective therapeutic option is in your hands. For a successful fight against bacterial infection, keep it for longer.

See Also

Amlodipine Side Effects

Sertraline Side Effects

Doxycycline Side Effects

Lisinopril Side Effects

Lexapro Side Effects

What is Meloxicam Used For?

Blood Thinners Side Effects

  1. Food and drug administration, AMOXIL Prescribing information, 2015 Sep,
  2. Pediatric Associates of the Northwest, Rashes On Amoxicillin – When Is It A True Allergy?
  3. Harvard T.H. Chan School of Public Health, The Microbiome
  4. MedlinePlus, Nausea and vomiting – adults, 2021 Jul,
  5. MedlinePlus, Nausea and Vomiting,
  6. Harvard medical school, Candidiasis, 2019 Jan,
  7. Cleveland Clinic, Crystals in Urine, 2021 Nov,
  8. Cleveland Clinic, Anemia, 2022 Sep,
  9. National Heart, Lung, and Blood Institute, Thrombocytopenia, 2022 Mar,,is%20called%20a%20blood%20clot.
  10. Cleveland Clinic, Eosinophilia, 2022 May,
  11. Cleveland Clinic, Agranulocytosis, 2022 Nov,
  12. MedlinePlus, Amoxicillin, 2022 Jan,
  13. Mayo Clinic, Phenylketonuria (PKU), 2022 May,
  14. Akhavan B.J., Khanna N.R., Vijhani P., Amoxicillin, Bookshelf ID: NBK482250PMID: 29489203,It%20is%20an%20amino-penicillin%2C%20created%20by%20adding%20an%20extra,negative%20coverage%20compared%20to%20penicillin
  15. National Library of Medicine, Leah R. Uto and Valerie Gerriets, Clavulanic Acid, 2022 Jun,
  16. K.Gupta et al., International Clinical Practice Guidelines for the Treatment of Acute Uncomplicated Cystitis and Pyelonephritis in Women: A 2010 Update by the Infectious Diseases Society of America and the European Society for Microbiology and Infectious Diseases, 2011 Mar,
  17. American Family Physician, R.Colgan MD and M.Williams, MD, Diagnosis and Treatment of Acute Uncomplicated Cystitis, 2011 Oct,
  18. American Urological Association, Recurrent Uncomplicated Urinary Tract Infections in Women: American Urological Association/Canadian Urological Association/Society of Urodynamics, Female Pelvic Medicine & Urogenital Reconstruction Guideline, 2022,
  19. Cleveland Clinic, Antibiotic resistance, 2021 May,

Follow us