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Flagyl® & Stevens-Johnson Syndrome (SJS)

January 4, 2021

Like most medications, Flagyl® may cause a variety of side effects. Some of these side effects can lead to complications that may be fatal. Among such severe side effects is Stevens-Johnson syndrome, which is a life-threatening skin reaction. Patients are reportedly at a higher risk of developing Stevens-Johnson syndrome if they take Flagyl® in conjunction with mebendazole (a drug prescribed to treat worm infestations, including tapeworm, hookworm and roundworms).


Generically known as metronidazole, Flagyl® is an antibiotic medication used to treat infections caused by anaerobic bacteria or protozoa. Specifically, Flagyl® is designed to treat infections of the stomach, skin, respiratory tract, joints and the vagina (though it's important to note that Flagyl® is not appropriate for the treatment of yeast infections). In the U.S., Flagyl® is distributed by Pfizer (worldwide it's distributed by Sanofi-Aventis also under the brand name Flagyl®).

Minor Flagyl® Side Effects

In addition to Stevens-Johnson syndrome, Flagyl® has been associated with a list of other side effects that may include the following:

  • Loss of appetite
  • Constipation
  • Headache
  • Dizziness
  • Upset stomach
  • Vomiting or nausea

Severe Flagyl® Side Effects

Patients should be advised to seek medical attention should they experience any of the following symptoms as they may be a sign of an allergic reaction in the form of Stevens-Johnson syndrome:

  • Red/purplish, blotchy skin rash
  • Blistered or peeling of the skin
  • Swelling of the face, mouth or tongue
  • Tightness in the chest
  • Sores in the mucous membranes of the eyes, nose, mouth or vagina
  • White patches in the mouth

Other serious side effects to watch out for may include:

  • Dry mouth
  • Nasal congestion
  • Abdominal cramping
  • Sudden weight loss
  • Depressed feelings
  • Confusion
  • Unexplained irritability
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