Isoniazid Tablets Side Effects Center

Last updated on RxList: 3/15/2022
Isoniazid Tablets Side Effects Center

What Is Isoniazid?

Isoniazid is an antibacterial recommended for all forms of tuberculosis in which organisms are susceptible. Active tuberculosis must be treated with multiple concomitant anti-tuberculosis medications to prevent the emergence of drug resistance. Isoniazid is recommended as preventive therapy for certain individuals. Isoniazid is available in generic form.

What Are Side Effects of Isoniazid?

Common side effects of isoniazid include:

Dosage for Isoniazid

The usual adult oral dosage of isoniazid to treat tuberculosis is 5 mg/kg up to 300 mg daily in a single dose; or 15 mg/kg up to 900 mg/day, two or three times/week. Isoniazid is used in conjunction with other effective anti-tuberculosis agents.

What Drugs, Substances, or Supplements Interact with Isoniazid?

Isoniazid may interact with alcohol, acetaminophen, carbamazepine, ketoconazole, phenytoin, theophylline, and valproate. Tell your doctor all medications and supplements you use.

Isoniazid During Pregnancy and Breastfeeding

Tell your doctor if you are pregnant or plan to become pregnant before using isoniazid. Isoniazid should be used as a treatment for active tuberculosis during pregnancy because the benefit justifies the potential risk to the fetus. Isoniazid passes into breast milk in small amounts but is not harmful to nursing infants. However, the amount that passes is so low it cannot be relied upon for prophylaxis or therapy of nursing infants. Consult your doctor before breastfeeding.

Additional Information

Our Isoniazid Side Effects Drug Center provides a comprehensive view of available drug information on the potential side effects when taking this medication.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.


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Get emergency medical help if you have signs of an allergic reaction (hives, difficult breathing, swelling in your face or throat) or a severe skin reaction (fever, sore throat, burning in your eyes, skin pain, red or purple skin rash that spreads and causes blistering and peeling).

Seek medical treatment if you have a serious drug reaction that can affect many parts of your body. Symptoms may include: skin rash, fever, swollen glands, flu-like symptoms, muscle aches, severe weakness, unusual bruising, or yellowing of your skin or eyes. This reaction may occur several weeks after you began using isoniazid.

Call your doctor at once if you have:

  • sudden weakness or ill feeling, or fever for 3 days or longer;
  • pain in your upper stomach (may spread to your back), nausea, loss of appetite;
  • dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes);
  • vision changes, pain behind your eyes;
  • confusion, memory problems, unusual thoughts or behavior;
  • a seizure (convulsions); or
  • pale skin, easy bruising or bleeding (nosebleeds, bleeding gums).

Common side effects may include:

  • numbness, tingling, or burning pain in your hands or feet;
  • nausea, vomiting, upset stomach; or
  • abnormal liver function tests.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.


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The most frequent reactions are those affecting the nervous system and the liver.

Nervous System Reactions

Peripheral neuropathy is the most common toxic effect. It is dose-related, occurs most often in the malnourished and in those predisposed to neuritis (e.g., alcoholics and diabetics) and is usually preceded by paresthesias of the feet and hands. The incidence is higher in “slow inactivators”.

Other neurotoxic effects, which are uncommon with conventional doses, are convulsions, toxic encephalopathy, optic neuritis and atrophy, memory impairment and toxic psychosis.

Hepatic Reactions

See BOXED WARNING. Elevated serum transaminase (SGOT; SGPT), bilirubinemia, bilirubinuria, jaundice and occasionally severe and sometimes fatal hepatitis. The common prodromal symptoms of hepatitis are anorexia, nausea, vomiting, fatigue, malaise and weakness. Mild hepatic dysfunction, evidenced by mild and transient elevation of serum transaminase levels occurs in 10 to 20 percent of patients taking isoniazid. This abnormality usually appears in the first 1 to 3 months of treatment but can occur at any time during therapy. In most instances, enzyme levels return to normal and generally, there is no necessity to discontinue medication during the period of mild serum transaminase elevation. In occasional instances, progressive liver damage occurs, with accompanying symptoms. If the SGOT value exceeds three to five times the upper limit of normal, discontinuation of the isoniazid should be strongly considered. The frequency of progressive liver damage increases with age. It is rare in persons under 20, but occurs in up to 2.3 percent of those over 50 years of age.

Gastrointestinal Reactions

Nausea, vomiting, epigastric distress, and pancreatitis.

Hematologic Reactions

Agranulocytosis; hemolytic, sideroblastic or aplastic anemia, thrombocytopenia; and eosinophilia.

Hypers ens itivity Reactions

Fever, skin eruptions (morbilliform, maculopapular, purpuric or exfoliative), lymphadenopathy, vasculitis, toxic epidermal necrolysis, and drug reaction with eosinophilia syndrome (DRESS).

Metabolic And Endocrine Reactions

Pyridoxine deficiency, pellagra, hyperglycemia, metabolic acidosis and gynecomastia.

Miscellaneous Reactions

Rheumatic syndrome and systemic lupus erythematosus-like syndrome.

Read the entire FDA prescribing information for Isoniazid Tablets (isoniazid)

© Isoniazid Tablets Patient Information is supplied by Cerner Multum, Inc. and Isoniazid Tablets Consumer information is supplied by First Databank, Inc., used under license and subject to their respective copyrights.

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