Key takeaways
The most common side effects of amoxicillin are skin rash, nausea, vomiting, and diarrhea. It may also cause allergic reactions or serious side effects, but those are less common.
Gastrointestinal side effects and non-allergic rashes typically develop within the first several days of treatment, and they often subside as the body adjusts, although diarrhea and an altered gut microbiome are potential long-term side effects.
To help avoid side effects, tell your healthcare provider about all other medical conditions and drugs, take amoxicillin only as directed, always take it with food, and watch out for signs of allergic reaction.
Amoxicillin (brand name: Amoxil) is a penicillin-like antibiotic that can treat bacterial infections of the ears, nose, sinuses, skin, lungs, urinary tract, and more. Most people tolerate it well, although there’s always a risk of side effects. Here’s what to watch for if you’ve been prescribed amoxicillin and how to avoid side effects.
Common side effects of amoxicillin
According to data from clinical trials, the most common side effects of amoxicillin are diarrhea, skin rash, vomiting, and nausea. But there are several other possible side effects, including:
- Headaches
- Upset stomach
- Tongue discoloration
- Yeast infection
- Elevated liver enzymes
- High white blood cell counts (eosinophilia)
Serious side effects of amoxicillin
Serious adverse effects are rare but are still possible and require immediate medical attention. The serious side effects of amoxicillin include:
- Superinfections (from antibiotic resistance)
- Severe diarrhea (including Clostridium difficile-associated diarrhea)
- Liver problems such as swelling (hepatitis) and obstructive jaundice (cholestatic jaundice)
- Blood disorders such as hemolytic anemia (rapid red blood cell death), low platelets, or agranulocytosis (low counts of a certain type of white blood cell)
- Seizures
- Swelling of the brain and spinal cord membranes (aseptic meningitis)
- Severe allergic reactions (trouble breathing, hives, racing heart, swollen lymph nodes, swelling of the face or throat, vomiting, stomach pain, etc.)
- Severe skin reactions like Stevens-Johnson Syndrome (SJS) and Toxic Epidermal Necrolysis (TEN)
If you notice any of these symptoms, get in touch with a healthcare provider as soon as possible.
How soon do amoxicillin side effects start?
The onset of amoxicillin side effects depends on the type of side effect. For example, “gastrointestinal side effects like nausea, diarrhea, and stomach pain will develop within the first several days of beginning treatment,” says James J. Chao, MD, FACS, cofounder and chief medical officer of VedaNu Wellness. He says allergic reactions can develop anywhere between one hour and 12 days after beginning amoxicillin, and non-allergic rashes usually develop around days three to seven. So even if you get through the first few days of treatment without any side effects, you’re not necessarily in the clear. You may still experience new side effects several days after your first dose.
How long do amoxicillin side effects last?
A typical course of amoxicillin lasts five to 10 days, depending on the infection, and most side effects will subside after treatment ends. Some amoxicillin side effects, however, are delayed and may take longer to resolve, such as allergic reactions, blood disorders, rashes, and diarrhea from C. difficile.
According to Dr. Chao, rashes can persist for several days after discontinuing treatment, and diarrhea has been known to persist and develop up to two months after treatment.
Some side effects, such as yeast infections, allergic reactions, blood problems, superinfections, or C. difficile infection, may require further medical treatment.
What are the long-term side effects of amoxicillin?
Some serious side effects of amoxicillin, like antibiotic-related diarrhea, can potentially last for a while or appear months after taking it. Liver issues and blood disorders that can stem from amoxicillin use may have long-term effects as well. Antibiotic resistance and gut microbiome alterations are also possible long-term effects of amoxicillin.
Some bacteria, like E. coli and some streptococcus species, can become resistant to amoxicillin in people who take it frequently. This can make treating those infections especially tricky in the future because of a developed resistance to this antibiotic.
Dr. Chao says that dysbiosis, or altered gut microbiota, is a long-term side effect that causes dramatic changes in the friendly bacteria in your gut. “Recovering from changes in your microbiome can take one to six months, depending on your diet and pre-treatment microbiome health,” Dr. Chao says. “While most people will see species diversity return to normal after two months, the makeup of your gut and medications passed during digestion can stay changed for much longer.”
Amoxicillin interactions
While Amoxicillin has several minor drug interactions, a few prescription drugs will cause problems when combined with amoxicillin:
- Oral contraceptives: Amoxicillin may reduce the effectiveness of oral contraceptives, though there is some disagreement in the research. Still, women on birth control are advised to use backup birth control when taking amoxicillin.
- Tetracyclines: Antibiotics such as doxycycline are generally avoided in combination with penicillins. These drugs, called tetracyclines, reduce the effectiveness of amoxicillin.
- Live vaccines: Live, weakened bacteria vaccines, such as BCG or typhoid vaccine, are less effective when given to a person taking amoxicillin. The bacteria are killed off before they can elicit a strong antibody response.
- Warfarin: Close monitoring is required when combining amoxicillin with warfarin. Many types of antibiotics, including amoxicillin, reduce the body’s ability to form blood clots when combined with warfarin, a blood-thinning drug. Other blood thinners, however, are safe to take with amoxicillin.
- Allopurinol: An allergic reaction to amoxicillin is more likely when it is combined with the gout medication, allopurinol. In some cases, allopurinol has even precipitated severe allergic reactions to amoxicillin.
Some amoxicillin drug interactions are beneficial. The gout medication probenecid increases the effectiveness of amoxicillin. Some people without gout may be prescribed both drugs to treat certain types of infections. The effectiveness of amoxicillin is also enhanced by aminoglycoside antibiotics.
Additionally, be mindful of your diet while taking amoxicillin, as certain foods can affect how it works. For example, grapefruit and grapefruit juice are known to interfere with the effectiveness of certain drugs, including antibiotics. Drinking alcohol in moderation typically won’t affect how penicillin drugs work, but it might exacerbate some of amoxicillin’s gastrointestinal side effects, so it’s often best to avoid it.
Coffee and amoxicillin don’t directly interact with each other, so your morning pick-me-up isn’t at risk. And some foods might actually help with certain side effects: Amoxicillin and bananas, rice, toast, or other bland foods (the BRAT diet) might help calm an upset stomach, nausea, or other gastrointestinal side effects.
Safety measures while using amoxicillin
Amoxicillin is FDA approved for use in both children and adults, including people over age 65. But anyone who has had a serious hypersensitivity reaction, like anaphylaxis or Stevens-Johnson syndrome, shouldn’t take it.
Other than that, amoxicillin is often safe, although certain groups should take it with caution. “Patients with kidney disease should be very cautious when taking antibiotics like amoxicillin,” Dr. Chao says. “Amoxicillin is cleared by the kidneys, so if your kidneys aren’t functioning at 100%, the medication doesn’t clear from your body as fast.”
People with Crohn’s disease and ulcerative colitis should also be careful, since antibiotic use may cause flare-ups, Dr. Chao says. “Basically, the medication strips good bacteria from your intestines, which is already compromised in these patients.”
While studies on mice show that amoxicillin might have negative effects on the ovaries, there’s very little evidence of those effects in humans. It is important to tell your healthcare provider if you are pregnant or planning to become pregnant, because when taken during the first trimester, it can increase the risk of certain congenital disabilities. While there is no evidence that amoxicillin will harm a breastfeeding baby, healthcare providers are cautious. Since the infant may develop allergies to the drug, a healthcare provider may choose a different antibiotic or encourage the mother to stop breastfeeding the infant while taking the antibiotic.
Taking too much amoxicillin can result in unpleasant side effects such as upset stomach and diarrhea, but usually does not cause serious problems. However, in rare cases, an amoxicillin overdose can damage the kidneys or result in renal failure. If an amoxicillin overdose is suspected, immediately call a poison control center.
How to avoid amoxicillin side effects
Side effects are common when taking amoxicillin or any other penicillin antibiotic. A few tips can help minimize these effects and help the drug work as well as possible.
1. Tell your healthcare provider about all medical conditions and medications
Start by informing the healthcare provider prescribing amoxicillin about all past and present medical conditions, especially:
- Kidney problems
- Drug allergies or reactions to antibiotics
- Mononucleosis
- Any history of diarrhea when taking antibiotics
- Gastrointestinal problems
- Gout
Some problems may arise when amoxicillin is combined with other drugs, but these drug interactions are uncommon. Always give the healthcare provider a complete list of all prescription and nonprescription medications you’re taking, especially birth control pills, antibiotics, or drugs that require precise dose adjustments, such as methotrexate or warfarin.
2. Take amoxicillin as directed
Your healthcare provider will give you instructions for taking amoxicillin, and you should follow them exactly. If you miss a dose, take it as soon as you remember, unless it is almost time for your next dose, and never double up to make up for a missed dose. Above all, take the medicine for the full duration of the prescription, even if your symptoms subside. This will ensure the bacterial infection is completely wiped out.
Most people need to take amoxicillin multiple times a day so that its concentration in the body stays high, continuously killing bacteria. Late or missed doses allow the bacteria to start growing again and increase the risk of the infection developing drug resistance. Amoxicillin may also be prescribed with other drugs, such as clarithromycin or lansoprazole, for certain infections. It is important to take all prescribed drugs on schedule. If there’s a problem with late or missed doses, a pharmacist can suggest alarms, apps, and other tools to help.
3. Do not use amoxicillin for other infections
Amoxicillin is effective against some bacterial infections but will not help eradicate other bacterial or viral infections. To avoid unnecessary side effects, take amoxicillin solely for the bacterial infection indicated. If any medicine is left over, don’t save it. Ask a pharmacist how to dispose of unused amoxicillin safely.
4. Take amoxicillin with food
You can technically take amoxicillin with or without food. But unless you’re instructed otherwise, take it with food, since this will help avoid side effects like nausea, vomiting, stomach cramps, and abdominal pain.
5. Watch for signs of an allergic reaction
Allergic reactions are among the most common side effects of amoxicillin and other penicillin antibiotics. Most are mild reactions, but they should still be taken seriously. Watch for signs of an allergic reaction, such as:
- Skin rash
- Hives
- Swelling
If you notice these symptoms (or any other signs of an allergic reaction), get medical advice as soon as you can. Get emergency medical help at any sign of trouble breathing, wheezing, lightheadedness, clammy skin, confusion, fever, sore throat, skin pain, or blistering.
6. Watch for diarrhea
Diarrhea is another common side effect of amoxicillin. Typically, this isn’t serious and responds to over-the-counter (OTC) antidiarrheal medications. It may, however, be a sign of a more serious problem if the diarrhea is watery or bloody. If this happens, see a healthcare provider immediately rather than treat the diarrhea on your own.
How to treat the side effects of amoxicillin
Most of amoxicillin’s most common side effects are mild, and you can treat them with OTC medications, dietary changes, or at-home remedies.
For upset stomach or other gastrointestinal side effects, taking amoxicillin with a meal or switching to a bland diet may help, as will OTC medicines like Pepto-Bismol. If you experience mild diarrhea, it’s important to stay hydrated with water or electrolyte beverages, and OTC anti-diarrheal medications like Imodium may also work.
Headaches are common as well, but OTC pain relievers like NSAIDs or acetaminophen can make them much more tolerable or eliminate them completely.
Skin rashes can be a little trickier, since amoxicillin can cause both non-allergic and allergic rashes. Hives from an allergic reaction will typically appear within hours, manifesting as raised, itchy patches. A non-allergic amoxicillin rash often appears days later as flat pink spots that may or may not itch. For a non-allergic rash, it’s generally okay to keep taking amoxicillin, and Benadryl can help with any itching. For hives from a serious allergic reaction, stop taking amoxicillin and see a healthcare provider right away. And if you’re having trouble breathing, swelling, dizziness, or a drop in blood pressure, seek emergency medical attention.
Bottom line: Is amoxicillin safe?
Yes, amoxicillin is generally very safe to take for certain infections, including pneumonia, bronchitis, tonsillitis, ear infections, skin infections, and urinary tract infections. As long as you take it exactly as your healthcare provider prescribes and keep an eye out for serious side effects like allergic reactions, it’s a safe and effective treatment. And if you experience any mild side effects, remember that they’re typically temporary and easily treatable.
Frequently asked questions about amoxicillin
Can amoxicillin cause diarrhea?
Yes, and it’s one of the drug’s most common side effects. Around 8% of patients experienced it in pediatric clinical trials.
Can amoxicillin cause UTIs?
Amoxicillin won’t directly cause a UTI, but taking it frequently might lead to certain antibiotic-resistant strains of the infection.
Can amoxicillin cause yeast infections?
Yes, amoxicillin can cause yeast infections by clearing out the good bacteria that typically moderate yeast growth.
Can amoxicillin cause a rash?
Rash is one of the most common side effects of amoxicillin. Most often, these rashes aren’t related to an allergic reaction, but sometimes they might be, so it’s important to pay close attention to their features and accompanying symptoms.
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