Antibiotics are prescription drugs that help treat infections caused by bacteria. Some of the more common infections treated with antibiotics include bronchitis, pneumonia, and urinary tract infections.

Antibiotics work by killing the bacteria causing the infection, or by stopping the bacteria from growing and multiplying.

Antibiotics only work to treat bacterial infections. They don’t work for infections caused by viruses, which can include:

  • common cold
  • runny nose
  • most coughs and bronchitis
  • flu

There are many different groups, or classes, of antibiotics. These classes have side effects and typically affect men and women the same way. However, certain side effects are more common from some antibiotics than from others.

Read on to learn about common side effects, how to manage them, and which antibiotics are more likely to cause them.

Stomach upset

Many antibiotics cause stomach upset or other gastrointestinal side effects. These can include:

Macrolide antibiotics, cephalosporins, penicillins, and fluoroquinolones may cause more stomach upset than other antibiotics.

What to do

Ask your doctor or pharmacist whether to take your antibiotic with food. Eating can help reduce stomach side effects from certain antibiotics such as amoxicillin and doxycycline (Doryx).

However, this approach won’t work for all antibiotics. Some antibiotics, such as tetracycline, must be taken on an empty stomach.

Talk to your doctor to make sure you know how you’re supposed to take your drug and if there are other ways you can ease stomach side effects.

When to call your doctor

Mild diarrhea usually clears up after you stop taking the drug. However, if the diarrhea is severe, it may cause:

  • abdominal pain and cramping
  • fever
  • nausea
  • mucus or blood in your stool

These symptoms can be caused by an overgrowth of harmful bacteria in your intestines. In these cases, call your doctor right away.


If you’re taking an antibiotic, such as tetracycline, your body can become more sensitive to light. This effect can make light seem brighter in your eyes. It can also make your skin more prone to sunburn.

Photosensitivity should go away after you finish taking the antibiotic.

What to do

If you know you’ll be out in the sun, take certain precautions to stay safe and comfortable.

Be sure to wear sunscreen with UVA and UVB protection, and reapply sunscreen as directed on the label.

Also, wear protective clothing and accessories, such as a hat and sunglasses.


Fevers are a common side effect of many medications, including antibiotics. A fever may occur because of an allergic reaction to a medication or as a bad side effect.

Drug fevers can occur with any antibiotic, but they’re more common with the following:

  • beta-lactams
  • cephalexin
  • minocycline
  • sulfonamides

What to do

If you get a fever while taking an antibiotic, it will likely go away on its own. But, if your fever doesn’t go away after 24 to 48 hours, ask your doctor or pharmacist about using over-the-counter pain relievers such as acetaminophen (Tylenol) or ibuprofen (Motrin) to help reduce the fever.

When to call your doctor

If you have a fever greater than 104°F (40°C), a skin rash, or trouble breathing, call your doctor or 911 right away.

Vaginal yeast infection

Antibiotics decrease the amount of a helpful bacteria, lactobacillus, in the vagina. This “good bacteria” helps keep a naturally occurring fungus called Candida in check. When this natural balance is tipped in favor of Candida growth a yeast infection may occur.

Symptoms include:

  • vaginal itching
  • burning during urination or sex
  • swelling around the vagina
  • soreness
  • pain during sex
  • redness
  • rash

A whitish-gray and clumpy discharge from the vagina, sometimes said to look like cottage cheese, is another sign you have a yeast infection.

What to do

For simple yeast infections, your doctor may prescribe a vaginal antifungal cream, ointment, suppository, or an oral tablet. Examples include:

  • butoconazole
  • clotrimazole
  • miconazole
  • terconazole
  • fluconazole

Many of the creams, ointments, and suppositories are also available without a prescription.

For severe or complicated yeast infections, your doctor may prescribe longer duration of medication treatment.

If the infection recurs, your sexual partner may also have a yeast infection. You should use condoms when having sex if you suspect either of you has a yeast infection.

Antibiotics such as tetracycline and doxycycline can cause permanent tooth staining in children whose teeth are still developing. This effect mostly occurs in children who are younger than 8 years of age.

If a pregnant woman takes these drugs, they may stain the developing child’s primary teeth.

What to do

Ask your doctor why they’re prescribing one of these antibiotics for you if you’re pregnant or for your child. Also, ask if there are other drug options that might work that don’t have this side effect.

Serious side effects from antibiotics aren’t common, but they can occur. Some of the main serious side effects include:

Allergic reactions

Allergic reactions are possible with any medication, including antibiotics. Some allergic reactions can be mild, but others can be serious and need medical attention.

If you’re allergic to a certain antibiotic, you’ll have symptoms right after taking the drug. These symptoms can include trouble breathing, hives, and swelling of your tongue and throat.

When to call your doctor

If you have hives, stop taking the drug and call your doctor. If you have swelling or trouble breathing, stop taking the drug and call 911 right away.

Stevens-Johnson syndrome

Stevens-Johnson syndrome (SJS) is a rare, but serious, disorder of the skin and mucous membranes. Mucous membranes are the moist linings of certain parts of your body, such as your nose, mouth, throat, and lungs.

SJS is a reaction that can happen with any medication, including antibiotics. It occurs more often with antibiotics such as beta-lactams and sulfamethoxazole.

Typically, SJS begins with flu-like symptoms, such as a fever or sore throat. These symptoms may be followed by blisters and a painful rash that spreads. Following that, the top layer of your skin can shed. Other symptoms can include:

  • hives
  • skin pain
  • fever
  • cough
  • swelling of your face or tongue
  • pain in your mouth and throat

What to do

You can’t prevent this condition, but you can try to reduce your risk.

You’re at increased risk for SJS if you have a weakened immune system, have had SJS in the past, or have a family history of SJS.

If you believe any of these conditions apply to you, talk to your doctor before taking an antibiotic.

When to call your doctor

Call 911 or go to the nearest emergency room right away if you have symptoms of SJS and think you have the condition.

Blood reactions

Some antibiotics can cause changes to your blood.

For example, leukopenia is a decrease in the number of white blood cells. It can lead to increased infections.

Another change is thrombocytopenia, which is a low level of platelets. This can cause bleeding, bruising, and slowed blood clotting.

Beta-lactam antibiotics and sulfamethoxazole cause these side effects more often.

What to do

You can’t prevent these reactions. However, you’re at higher risk if you have a weakened immune system. If your immune system is weak, discuss it with your doctor before you take an antibiotic.

When to call your doctor

Call your doctor if you have a new infection or one that appears abruptly after taking an antibiotic.

Call 911 or go to the nearest emergency room right away if you:

  • have serious bleeding that doesn’t stop
  • have bleeding from your rectum
  • cough up a substance like coffee grounds

Heart problems

In rare cases, certain antibiotics can cause heart problems such as an irregular heartbeat or low blood pressure.

The antibiotics most often linked with these side effects are erythromycin and some fluoroquinolones such as ciprofloxacin. The antifungal terbinafine can also cause this problem.

What to do

If you have an existing heart condition, tell your doctor before you start taking any kind of antibiotic. This information will help your doctor choose the right antibiotic for you.

When to call your doctor

Call your doctor if you have new or worsening heart pain, an irregular heart rhythm, or trouble breathing. If your symptoms are severe, call 911 or go to the nearest emergency room.


Tendonitis is inflammation or irritation of a tendon. Tendons are thick cords that attach bone to muscle, and they can be found throughout your body.

Antibiotics such as ciprofloxacin have been reported to cause tendonitis or tendon rupture. This is when the tendon tears or rips.

All people are at risk for tendon problems when taking certain antibiotics. However, certain people are at increased risk of tendon rupture. These include people who:

  • have existing kidney failure
  • have had a kidney, heart, or lung transplant
  • have had past tendon problems
  • are taking steroids
  • are older than 60 years

What to do

Talk to your doctor before starting a new antibiotic if you meet any of the increased risk factors. This information will help your doctor choose the correct antibiotic for you.

When to call your doctor

If you have new or worsening tendon pain after taking your antibiotic, call your doctor. If the pain is severe, go to the nearest emergency room.


It’s rare for antibiotics to cause seizures, but it can happen. Seizures are more common with ciprofloxacin, imipenem, and cephalosporin antibiotics such as cefixime and cephalexin.

What to do

If you have epilepsy or a history of seizures, be sure to tell your doctor before you start taking any kind of antibiotic. That way, your doctor can choose an antibiotic that won’t make your condition worse or interact with your seizure medications.

When to call your doctor

Call your doctor if you have new seizures or your seizures get worse when you take an antibiotic.

If your doctor prescribes antibiotics for you, know that there are ways to manage side effects. Some questions you may want to ask your doctor about antibiotic side effects include:

  • Am I likely to have side effects with this drug?
  • What are your suggestions for dealing with side effects?
  • Are there any antibiotics that could help me that are known to have fewer side effects?

It may also help to show your doctor this article and discuss it. Together, you can manage any side effects you may have from your antibiotic.


If I have bad side effects from my antibiotic, can I stop taking the medication?

Anonymous patient


That’s a big “No.” You should never stop taking an antibiotic without first talking with your doctor.

Stopping an antibiotic treatment before it’s finished can cause the infection to return, perhaps even stronger than before. If it returns, it could be resistant to the antibiotic you were taking. That means the drug wouldn’t work to treat your infection.

Bad side effects from your antibiotic can be difficult, though, so call your doctor. They can suggest ways to reduce your side effects. If those don’t work, they may suggest another medication. The important part is to finish your full course of antibiotics.

Healthline Medical TeamAnswers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.
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