What Are the Side Effects of Taking Antibiotics?

Antibiotics can help fight bacterial infections that won't clear up on their own, but they can have side effects ranging from mild to severe.

Antibiotics are drugs that help treat certain bacterial infections such as strep throat, whooping cough, or urinary tract infections. The medications work by killing bacteria or preventing the bacteria from growing. They can also cause a multitude of side effects, ranging from mild to severe. Taking precautions may help you avoid or better manage certain side effects.

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Antibiotic Side Effects

Knowing which side effects you might experience when taking antibiotics can help you identify whether you’re experiencing any reaction to the medication. Being able to identify the symptoms can also help you know when to get medical attention.


Headaches are a common side effect of taking certain antibiotics. These antibiotics include:

Augmentin (amoxicillin plus clavulanate): This treats bacterial infections of the ears, lungs, sinus, skin, and urinary tract, and certain sexually transmitted infections (STIs).

Keflex (cephalexin): This treats pneumonia and other respiratory tract infections.

Monurol (fosfomycin): This treats urinary tract infections.

Nitrofurantoin: This treats urinary tract infections. Brand names include Furadantin, Macrobid, and Macrodantin.

Vancomycin: This treats bacteria-caused colitis and inflammation of the colon. Brand names include Firvanq and Vancocin.

Quinolones: This group of antibiotics includes norfloxacin, ciprofloxacin, levofloxacin, and moxifloxacin which all treat different types of bacterial infections.

If your antibiotic treatment is causing headaches, over-the-counter (OTC) painkillers like Tylenol or Motrin may help bring relief.

Digestive Problems

Most antibiotics can cause a range of gastrointestinal issues. Some side effects may include:

  • Abdominal discomfort
  • Abdominal pain
  • Lack of appetite
  • Bloating
  • Constipation
  • Nausea and vomiting
  • Diarrhea

While you may not be able to completely avoid gastrointestinal distress while taking antibiotics, you can help manage your symptoms. Staying hydrated can help manage some digestive issues.

If you're experiencing severe digestive upset that doesn't go away, speak with a healthcare provider. This could be a sign of Clostridium difficile, an antibiotic-resistant bacterial infection that causes diarrhea that can lead to severe colon damage. This infection can even be life-threatening.

Sensitivity to Sunlight

Some antibiotics can cause photosensitivity, meaning your eyes and skin become more sensitive to sunlight. Photosensitivity can cause skin irritations or even an allergic reaction due to sun exposure, though that reaction may be delayed up to several days.

Antibiotics that may cause photosensitivity include:

  • Cipro (ciprofloxacin): This treats pneumonia, gonorrhea, infectious diarrhea, and bacterial infections of the skin, bone, joint, abdomen, and prostate.
  • Levofloxacin: This treats pneumonia, and bacterial infections of the kidneys, prostate, and skin.
  • Ofloxacin: This treats pneumonia, and bacterial infections of the skin, bladder, reproductive organs, and prostate.
  • Primsol (trimethoprim): This treats urinary tract infections, traveler’s diarrhea, and can be used in combination with other drugs to treat pneumonia.
  • Achromycin V (tetracycline): This treats pneumonia, infections of the skin, eye, lymphatic, intestinal, genital, and urinary systems, and certain infections carried by ticks, lice, and mites.
  • Doxycycline: This is used to treat or prevent anthrax. It can also be used with other medications to treat rosacea.

It is not possible to prevent the development of photosensitivity while taking antibiotics, but you can take steps to protect yourself from its effects by limiting sun exposure. You can take precautions against the sun by:

  • Wearing UV-protected sunglasses to shield your eyes
  • Choosing long-sleeved shirts and long pants when going out in the sun
  • Opting for a broad-spectrum sunscreen that is SPF 30 or higher to protect against UV rays
  • Staying in the shade or indoors when the sun is at its strongest, between 10 a.m. and 4 p.m.
  • Grabbing a wide-brimmed hat to keep the sun off your head and face

Yeast Infections and Other Fungal Infections

Antibiotics work to fight bacteria causing your infection, but they can also kill off the “good” bacteria in your body. By getting rid of beneficial bacteria, antibiotics can make you more likely to develop a fungal infection like a yeast infection.

Here are a few things you can do to prevent this from happening:

  • Ask your doctor about taking an antifungal with your antibiotics if you're prone to fungal infections.
  • Avoid taking antibiotics unless absolutely necessary.
  • Practice good hygiene like promptly changing out of wet or sweaty clothes.

Tooth Staining

Older-class tetracycline antibiotics may cause permanent tooth staining in children under 8 years old.

Evidence suggests that a short course of doxycycline, a newer type of tetracycline, doesn't cause teeth-related side effects like staining.

Make sure to talk to a healthcare provider about the risk of tooth staining before taking tetracycline.


Research shows there may be a link between tendon damage and antibiotics, though this side effect is uncommon.

One study suggests that the antibiotic levofloxacin may increase the risk of tendon ruptures. Levofloxacin is part of a group of antibiotics called fluoroquinolones. Other antibiotics within this same class are not associated with the same risk.


There may also be some complications while taking antibiotics. Here are a few potential reactions to keep in mind. 

Medication Interactions

Taking antibiotics alongside other medications can sometimes have harmful effects. A healthcare provider or a pharmacist can tell you whether antibiotics will interact with your current medications.

Some antibiotics may interact with blood thinners. For example, taking the antibiotic cephalosporin may not be safe if you are currently taking a blood thinner such as Warfarin.

One type of antibiotic, rifamycin, may interact with birth control pills by lowering the pill’s effectiveness.

Additionally, tetracyclines, macrolides, and fluoroquinolones can interact with various medications.

Avoid mixing alcohol with antibiotics since this may increase your risk of adverse effects like nausea, headache, and dizziness. In some cases, alcohol may reduce the efficacy of certain antibiotics. However, the relationship between alcohol and antibiotics needs more research.

Allergic Reactions

Some people are allergic to certain antibiotics. Healthcare providers will typically ask whether you're allergic to antibiotics before prescribing them. If you've never taken them before, you might not know you have an allergy until you develop symptoms of a reaction.

A mild allergic reaction might involve:

  • Hives
  • Itching
  • Skin rash
  • Skin flushing

A severe reaction to antibiotics can be life-threatening. Signs of a severe allergic reaction, or anaphylaxis, may include hives; swelling of the tongue, throat, or lips; trouble breathing, or difficulty swallowing.

If you're having what you suspect is an allergic reaction to antibiotics, seek immediate medical care.

Bacterial Resistance

Overuse of antibiotics can contribute to bacterial resistance, leaving people vulnerable to serious complications from bacterial infections.

Bacterial resistance occurs when bacteria in your body develop a defense against antibiotics. This can cause antibiotics to become ineffective against new bacterial infections. Bacteria can then instead grow and multiply.

A Quick Review

Antibiotics are drugs that help treat certain bacterial infections such as strep throat or a urinary tract infection by killing bacteria or preventing the bacteria from growing. Like most other medications, antibiotics can cause certain side effects, some more serious than others. These side effects may include a headache, digestive problems, or a rash on the skin. 

There are ways to limit your risk of experiencing minor side effects. For instance, taking OTC pain relievers can help treat a headache. Taking OTC medicines like Pepto-Bismol can help treat diarrhea while taking antibiotics.

Antibiotics can also lead to complications, such as medication interactions, allergic reactions, and risk for bacterial resistance. 

If you are concerned about your side effects, talk to a healthcare provider about your options. 

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