Cephalexin is a generic drug that’s prescribed for certain bacterial infections in adults and children. As with other drugs, cephalexin can cause side effects, such as diarrhea, nausea, or vomiting.

Cephalexin is not available in a brand-name version.

The active ingredient in cephalexin is cephalexin. Cephalexin comes as an oral tablet, oral capsule, and oral liquid suspension.

Read on to learn about potential common, mild, and serious side effects of cephalexin. For a general overview of the drug, including details about its uses, see this cephalexin article.

Cephalexin can cause certain side effects, some of which are more common than others. These side effects may be temporary, lasting a few days to weeks. However, if the side effects last longer than that, bother you, or become severe, be sure to talk with your doctor or pharmacist.

These are just a few of the more common side effects reported in cephalexin oral capsule, powder for oral suspension, and oral tablet clinical trials:

  • abdominal pain
  • diarrhea (See the “Cephalexin: Side effect specifics” section)
  • gastritis (stomach irritation)
  • indigestion
  • nausea or vomiting

Mild side effects can occur with cephalexin use. This list doesn’t include all possible mild side effects of the drug. For more information, you can refer to the prescribing information for cephalexin oral capsule, powder for oral suspension, and oral tablet.

Mild side effects that have been reported with cephalexin include:

  • abdominal pain
  • diarrhea*
  • dizziness
  • fatigue
  • gastritis (stomach irritation)
  • headache
  • indigestion
  • nausea or vomiting
  • vaginitis*

These side effects may be temporary, lasting a few days to weeks. However, if the side effects last longer than that, bother you, or become severe, be sure to talk with your doctor or pharmacist.

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks and reviews the side effects of the medication. If you develop a side effect while taking cephalexin and want to tell the FDA about it, visit MedWatch.

* For more information about this side effect, see “Cephalexin: Side effect specifics.”

Cephalexin may cause serious side effects. The list below may not include all possible serious side effects of the drug. For more information, you can refer to the prescribing information for cephalexin oral capsule, powder for oral suspension, and oral tablet.

If you develop serious side effects while taking cephalexin, call your doctor right away. If the side effects seem life threatening or you think you’re having a medical emergency, immediately call 911 or your local emergency number.

Serious side effects that have been reported and their symptoms include:

  • hemolytic anemia (destruction of red blood cells), which may include symptoms such as:
    • fast heart rate
    • fatigue
    • jaundice (yellowing of the skin or whites of the eyes)
    • shortness of breath
  • kidney problems that are usually reversible, which may include symptoms such as:
    • blood in the urine
    • changes in the amount of urine you make
    • fever
    • sudden, unintentional weight gain due to fluid buildup
  • temporary liver problems, which may include symptoms such as:
    • dark colored urine
    • fatigue
    • fever
    • jaundice (yellowing of the skin or whites of the eyes)
    • nausea or vomiting
  • yeast infections of the genitals, which may include symptoms such as:
    • burning, itching, or irritation of the genitals
    • painful genitals
    • sores on the genitals
    • thick, white discharge from the vagina or in folds on the penis that resembles cottage cheese
  • Clostridium difficile (C. diff)-associated diarrhea (See the “Cephalexin: Side effect specifics” section)
  • hallucinations (seeing or hearing things that aren’t really there)
  • seizures
  • severe bleeding
ALLERGIC REACTION

For some people, cephalexin can cause an allergic reaction.

In general, symptoms of an allergic reaction can be mild or serious.

Ways to manage

For mild allergic reaction symptoms, such as a mild rash, call your doctor right away. They may recommend treatments to help manage your symptoms. They’ll also let you know whether you should keep taking the medication.

For severe allergic reaction symptoms, such as swelling or trouble breathing, call 911 or your local emergency number right away. These symptoms require immediate medical care because they can become life threatening. If you’ve had a serious allergic reaction to cephalexin, your doctor may recommend taking a different medication instead.

Penicillin allergy

If you have an allergy to penicillin, there’s a chance you could also experience an allergic reaction to cephalexin. Be sure to tell your doctor about all of your drug allergies.

Cephalexin may cause several side effects. Here are some frequently asked questions about the drug’s side effects and their answers.

Are cephalexin side effects in older people different than in younger adults?

In general, the side effects of cephalexin are the same in people age 65 years and older as they are in younger adults. In cephalexin oral capsule, powder for oral suspension, and oral tablet clinical trials, there were no differences in safety in older adults compared to younger adults.

That said, it’s possible that older adults might be more sensitive to some of the side effects of cephalexin. This is because kidney function tends to decrease with age, and the kidneys clear cephalexin from the body. With slowed kidney function due to age, more cephalexin can stay in the body for a longer time. This increases the risk of side effects.

If you have concerns about taking cephalexin due to your age, talk with your doctor.

How long does it take for cephalexin side effects to go away?

It depends. Most often, the side effects of cephalexin are mild and will go away once you have finished the course of it. However, it’s possible to have certain side effects after stopping cephalexin. These side effects can be serious and include:

  • C. diff-associated diarrhea (See the “Cephalexin: Side effect specifics” section)
  • hemolytic anemia (destruction of red blood cells)
  • yeast infections of the genitals

Talk with your doctor or pharmacist if you have side effects that aren’t going away after stopping cephalexin.

Learn more about some of the side effects that cephalexin may cause. To find out how often side effects occurred in clinical trials, see the prescribing information for cephalexin oral capsule, powder for oral suspension, and oral tablet.

Diarrhea and Clostridium difficile-associated diarrhea

Diarrhea is the most common side effect of cephalexin. In most cases, diarrhea isn’t serious and gets better once you finish taking cephalexin. However, there’s a serious form of diarrhea that can happen with antibiotics, including cephalexin. It’s called C. diff–associated diarrhea.

Antibiotic treatment can affect normal bacteria that grow in the large intestine. Sometimes, this allows an overgrowth of dangerous bacteria, called C. diff, which causes diarrhea. C. diff-associated diarrhea can range from mild to severe. In severe cases, colitis (inflammation of the large intestine) can occur, which can be fatal.

Symptoms of C. diff-associated diarrhea include:

  • abdominal pain or cramping that may be severe
  • dehydration
  • fast heart rate
  • fever
  • frequent watery diarrhea that may also be bloody
  • loss of appetite
  • unintentional weight loss

C. diff-associated diarrhea can happen while you’re taking antibiotics or up to two months afterward.

What you can do

If you develop diarrhea during or after cephalexin treatment, call your doctor. They can determine the most likely cause and suggest ways to manage it.

If you have symptoms of C. diff-associated diarrhea, get medical care right away.

Vaginitis

Vaginitis is irritation of the vagina. There are many causes of vaginitis, including infections and other irritants. When you’re taking an antibiotic, such as cephalexin, a yeast infection is often the cause of vaginitis. This side effect was not common in the drug’s studies.

Symptoms of vaginitis may include:

  • discharge
  • itchiness
  • pain during sex
  • urinary symptoms, such as burning or discomfort during urination

What you can do

If you experience symptoms of vaginitis, talk with your doctor. They’ll likely recommend ways to treat your symptoms.

Below is important information you should consider before taking Cephalexin.

Other precautions

Before taking Cephalexin, discuss your health history with your doctor. Cephalexin may not be right for you if you have certain medical conditions or other factors affecting your health. Be sure to talk with your doctor if any of the following apply to you:

Disclaimer: Medical News Today has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.