Health Guide

Isoniazid (By mouth)

Isoniazid (eye-soe-NYE-a-zid)

Treats tuberculosis (TB).

Brand Name(s):

There may be other brand names for this medicine.

When This Medicine Should Not Be Used:

You should not use this medicine if you have ever had an allergic reaction to isoniazid or reactions such as fever, chills, or arthritis from taking this medicine. You should not use isoniazid if you have liver damage from taking it before, or if you have severe liver disease of any type.

How to Use This Medicine:

Tablet, Liquid

  • Your doctor will tell you how much medicine to take and how often. It is very important to take this medicine on a regular schedule.
  • You may need to take isoniazid for several weeks or months. Keep taking it even if you have no symptoms. Your doctor will tell you when you can stop taking it.
  • Take on an empty stomach (1 hour before or 2 hours after a meal). May be taken with food to avoid stomach upset.
  • Shake the oral liquid well just before each use. Measure the dose using a marked measuring spoon or medicine cup.

If a dose is missed:

  • Take the missed dose as soon as possible.
  • Skip the missed dose if it is almost time for your next regular dose.
  • You should not use two doses at the same time.

How to Store and Dispose of This Medicine:

  • Store at room temperature, away from heat, moisture, and direct light. Do not freeze.
  • Keep all medicine out of the reach of children.

Drugs and Foods to Avoid:

Ask your doctor or pharmacist before using any other medicine, including over-the-counter medicines, vitamins, and herbal products.

  • Do not drink alcohol while taking isoniazid.
  • Make sure your doctor knows if you are taking blood thinners (such as Coumadin®), birth control pills, Dilantin®, or Antabuse®.
  • If you take antacids (such as Mylanta®, Maalox®, or Amphojel®), wait at least 1 hour after taking them before taking your isoniazid dose.
  • Foods such as cheese (Swiss, Cheshire, or Gruyere) or fish (tuna or skipjack) may cause headache, flushing, pounding heartbeat, sweating, dizziness, chills, or diarrhea. If you have these symptoms, call your doctor.

Warnings While Using This Medicine:

  • If you are pregnant or breastfeeding, talk to your doctor before taking this medicine.
  • Check with your doctor before taking if you have kidney or liver disease, or if you are being treated for seizures.
  • Isoniazid can cause liver problems. It is very important that you see your doctor on a regular schedule and have blood tests done as ordered.
  • Isoniazid can affect the results of some urine sugar tests. If you have diabetes do not change your medicine or diet unless you have checked with your doctor.
  • If you notice tingling, numbness, or pain in your hands or feet, contact your doctor.

Possible Side Effects While Using This Medicine:

Call your doctor right away if you notice any of these side effects:

  • Yellow skin or eyes
  • Dark or amber-colored urine
  • Severe stomach pain, nausea and vomiting
  • Weakness
  • Blurred vision, eye pain
  • Fever

If you notice these less serious side effects, talk with your doctor:

  • Stomach pain
  • Diarrhea

If you notice other side effects that you think are caused by this medicine, tell your doctor

Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088

Last Updated: 7/4/2018
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