What Are the Most Common Isoniazid Side Effects?

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  • Written By: Meshell Powell
  • Edited By: Melissa Wiley
  • Last Modified Date: 21 February 2020
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The most common isoniazid side effects include dizziness, insomnia, and stomach upset, although more serious side effects may also occur. This antibiotic may also cause nerve inflammation, seizures, and difficulty urinating. Elevated blood sugar levels, abnormal blood test results, and psychosis are among the potential isoniazid side effects and may be more pronounced when this drug is combined with certain other medications. Life-threatening liver damage has been reported among some people using this antibiotic. Any new or bothersome isoniazid side effects should be reported to a doctor for further medical evaluation.

Digestive problems are among the most frequently reported isoniazid side effects and may include nausea, vomiting, or heartburn. Abdominal cramps, constipation, and diarrhea have also been documented. Persistent vomiting or diarrhea, especially if blood is present, should be evaluated by a medical professional to rule out stomach or intestinal damage. Severe abdominal pain accompanied by fever should prompt a visit to a doctor or emergency department at the nearest hospital.

Blood disorders may develop as isoniazid side effects and often resolve themselves after the medication has been discontinued. Elevated blood sugar levels and decreased levels of vitamin B6 are the most common blood-related problems associated with the use of this drug. Women may notice menstrual irregularities and should not use this medication if pregnant or breastfeeding. Patients with diabetes or other diseases affecting the blood may not be able to safely use isoniazid.


Mental changes and mood swings should be reported to a doctor immediately, as these isoniazid side effects almost always require treatment with a different antibiotic. Confusion, irritability, and psychosis caused by this medication can lead to destructive behavior and often require emergency medical care. If a patient taking isoniazid becomes combative or exhibits signs of self-injury, emergency medical services should be contacted for transportation assistance to the nearest hospital.

Severe liver damage may occur as a result of this drug, and this risk increases with prolonged use. Jaundice is characterized by a yellow tint affecting the skin or the white portion of the eyes and often indicates that the liver is not able to function properly. This damage can be fatal and sometimes requires a liver transplant in order to save the life of the patient. Those who already have impaired renal function may experience complete kidney failure when using this medication. Dialysis or transplant may be needed if the medication is not discontinued before permanent kidney damage develops.


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