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Drug Profile

The information on this site is intended to supplement and enhance, not replace, the advice of a physician who is familiar with your medical history. Decisions about your health should always be made ONLY after detailed conversation with your doctor.

Generic drug name: isoniazid (eye soe NYE a zid)
GENERIC: available FAMILY: Drugs for Tuberculosis
Find the drug label by searching at DailyMed.

Pregnancy and Breast-feeding Warnings [top]

Pregnancy Warning

Isoniazid crossed the placental barrier and caused harm to developing fetuses in animal studies. Because of the potential for serious adverse effects to the fetus, this drug should not be used by pregnant women.

Breast-feeding Warning

Isoniazid is excreted in human milk. Because of the potential for serious adverse effects in nursing infants, you should not take this drug while nursing.

Safety Warnings For This Drug [top]


Severe and sometimes fatal hepatitis associated with isoniazid therapy may occur and may develop even after many months of treatment. The risk of developing hepatitis is age related. Approximate case rates by age are: 0 per 1,000 for persons under 20 years of age, 3 per 1,000 for persons in the 20–34 year age group, 12 per 1,000 for persons in the 35–49 year age group, 23 per 1,000 for persons in the 50–64 year age group, and 8 per 1,000 for persons over 65 years of age. The risk of hepatitis is increased with daily consumption of alcohol. Precise data to provide a fatality rate for isoniazid-related hepatitis is not available; however, in a U.S. Public Health Service Surveillance Study of 13,838 persons taking isoniazid, there were 8 deaths among 174 cases of hepatitis.

Therefore, patients given isoniazid should be carefully monitored and interviewed at monthly intervals. Serum transaminase concentration becomes elevated in about 10–20% of patients, usually during the first few months of therapy, but it can occur at any time. Usually enzyme levels return to normal despite continuance of drug, but in some cases progressive liver dysfunction occurs. Patients should be instructed to report immediately any of the prodromal symptoms of hepatitis, such as fatigue, weakness, malaise, anorexia, nausea, or vomiting. If these symptoms appear or if signs suggestive of hepatic damage are detected, isoniazid should be discontinued promptly, since continued use of the drug in these cases has been reported to cause a more severe form of liver damage.

Patients with tuberculosis should be given appropriate treatment with alternative drugs. If isoniazid must be reinstituted, it should be reinstituted only after symptoms and laboratory abnormalities have cleared. The drug should be restarted in very small and gradually increasing doses and should be withdrawn immediately if there is any indication of recurrent liver involvement. Treatment should be deferred in persons with acute hepatic diseases.[1]


There have been a number of case reports of liver damage involving a possible drug interaction between isoniazid, a medication used to prevent and treat tuberculosis (TB), and acetaminophen, an over-the-counter painkiller and the active ingredient in Tylenol. Isoniazid alone, especially as people get older, has been documented to cause liver damage. Acetaminophen, alone in large doses or probably in combination with alcohol, also increases the risk of liver damage. The combination of acetaminophen with isoniazid, according to the authors of these case reports, may also be dangerous.

If you are taking isoniazid for tuberculosis or have a positive TB skin test and are using the drug, consult your physician before using acetaminophen or any combination product containing acetaminophen. Discuss alternatives to acetaminophen with your physician.


If you have nausea, vomiting, yellow eyes, dark urine, unexplained fatigue, or abdominal pain, stop taking this medication and call your doctor immediately. These are symptoms of possible liver toxicity.

Facts About This Drug [top]

Isoniazid is used to treat and prevent tuberculosis (TB). If you are an older adult who has had a positive TB skin test, you do not necessarily need preventive treatment for TB. You should be treated only if you are at special risk, for example, if you have cancer, if you are taking high doses of corticosteroid drugs on a long-term basis, or if you had a negative TB skin test until recently. If you have sudden, serious liver disease, you should not get preventive TB treatment.


Isoniazid is used to treat and prevent tuberculosis (TB). If you are an older adult who has had a positive TB skin test, you do not necessarily need preventive treatment for TB. You should be treated only if you are at special risk, for example, if you have cancer, if you are taking high doses of corticosteroid drugs on a long-term basis, or if you had a negative TB skin test until recently. If you have sudden, serious liver disease, you should not get preventive TB treatment.

Isoniazid can cause serious damage to your liver. Some people who have taken this drug, especially people over age 50, have developed severe and even fatal hepatitis (a liver disease). You are more likely to get hepatitis if you drink alcohol daily, so do not drink while taking this drug. Call your doctor immediately if you have any of the symptoms of hepatitis: fatigue, weakness, malaise (vague feeling of being unwell), loss of appetite, nausea, vomiting, or yellow eyes or skin. Schedule monthly visits with your doctor while taking this drug. If you have impaired liver function or severe kidney failure, you should probably be taking less than the usual adult dose of isoniazid.

A small number of people using isoniazid develop nerve pain and tenderness in their hands and feet. Taking 15 to 50 milligrams of vitamin B6 every day can prevent this problem. If necessary, your doctor can give you a prescription for vitamin B6 along with the isoniazid prescription.

Before You Use This Drug [top]

Tell your doctor if you have or have had:

  • pregnancy or are breast-feeding
  • an unusual reaction to isoniazid, ethionamide, pyrazinamide, niacin, or other chemically related drugs
  • liver problems
  • alcohol dependence
  • epilepsy or seizures
  • severe kidney disease
  • diabetes (drug can affect test results)

Tell your doctor about any other drugs you take, including aspirin, herbs, vitamins, and other nonprescription products.

When You Use This Drug [top]

  • Do not drink alcohol.
  • You may need more vitamin B6 and niacin than usual. Ask your doctor.
  • If you plan to have any surgery, including dental, tell your doctor that you take this drug.
  • Check with your doctor if you have flushing after eating cheese or fish.
  • Have regular visits with your eye doctor if you have problems with vision.
  • Check with your doctor immediately if you have loss of appetite, nausea or vomiting, or unusual tiredness or weakness.
  • Check with your doctor if there is no improvement within two to three weeks.

How to Use This Drug [top]

  • If you miss a dose, take it as soon as you remember, but skip it if it is almost time for the next dose. Do not take double doses.
  • Do not share your medication with others.
  • Take the drug at the same time(s) each day.
  • Take with food if gastrointestinal irritation occurs.
  • If you take aluminum-containing antacids, take them at least one hour before or after you take your isoniazid.
  • Take pyridoxine to prevent or minimize nerve problems
  • Take this drug for the prescribed length of time, which may be six months to two years. If you stop too soon, your symptoms could come back.
  • Store at room temperature with lid on tightly. Do not store in the bathroom. Do not expose to heat, moisture, or strong light. Keep out of reach of children.

Interactions with Other Drugs [top]

The following drugs, biologics (e.g., vaccines, therapeutic antibodies), or foods are listed in Evaluations of Drug Interactions 2003 as causing “highly clinically significant” or “clinically significant” interactions when used together with any of the drugs in this section. In some sections with multiple drugs, the interaction may have been reported for one but not all drugs in this section, but we include the interaction because the drugs in this section are similar to one another. We have also included potentially serious interactions listed in the drug’s FDA-approved professional package insert or in published medical journal articles. There may be other drugs, especially those in the families of drugs listed below, that also will react with this drug to cause severe adverse effects. Make sure to tell your doctor and pharmacist the drugs you are taking and tell them if you are taking any of these interacting drugs:

carbamazepine, DILANTIN, GLUCOPHAGE, GLUCOVANCE, itraconazole, METAGLIP, metformin, phenytoin, RIFADIN, rifampin, RIMACTANE, SPORANOX, TEGRETOL.

The following acetaminophen-containing drugs should not be taken with isoniazid (see warning box): acetaminophen, ESGIC, FIORICET, PERCOCET, TYLENOL, TYLENOL NO. 3, TYLOX, VICODIN

Adverse Effects [top]

Call your doctor immediately if you experience:

  • numbness, tingling, pain, or weakness in hands or feet
  • clumsiness or unsteadiness
  • dark urine
  • yellow eyes or skin
  • loss of appetite
  • light-colored stools
  • headache
  • pain in stomach or abdomen
  • unexplained fatigue
  • nausea or vomiting
  • abnormal tiredness or weakness
  • blurred or changed vision
  • seizures
  • fever or sore throat
  • joint pain
  • depression, mood, or other mental changes
  • skin rash
  • Caution diabetics: Isoniazide may increase blood sugar.
  • unusual bleeding or bruising

Call your doctor if these symptoms continue:

  • nausea or vomiting
  • diarrhea
  • stomach pain

Signs of overdose:

  • severe nausea or vomiting
  • dizziness
  • slurred speech
  • unusual tiredness or weakness
  • seizures
  • confusion
  • coma

If you suspect an overdose, call this number to contact your poison control center: (800) 222-1222.

Periodic Tests[top]

Ask your doctor which of these tests should be done periodically while you are taking this drug:

  • liver function tests, before treatment and regularly thereafter (during nine months of treatment, you should have them at the end of months one, three, six, and nine)
  • ophthalmologic exams

last reviewed October 31, 2023