What is Isoniazid?

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  • Written By: Jacquelyn Gilchrist
  • Edited By: O. Wallace
  • Last Modified Date: 11 October 2019
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Isoniazid is a medication used to treat tuberculosis (TB). It may also be used as a preventative measure for those who have had contact with a person infected with TB. This antibiotic works by inhibiting the TB bacteria from growing and multiplying. Since it can only treat active tuberculosis infections, people with inactive infections may need to continue treatment for up to a year.

This medication is typically taken once daily with a full glass of water. It should be taken on an empty stomach, unless it causes upset stomach. Isoniazid is available in a tablet or a capsule, and patients who have difficulty swallowing may use the syrup form. Often, the doctor will prescribe a B6 vitamin along with this treatment to counteract potential numbness or tingling.

Alcohol should be strictly avoided while a person is taking isoniazid, as it may be more likely to cause liver damage. Certain foods must also be avoided or eaten with caution, such as ginseng, chocolate, and soy products. Prepared meats, chicken livers, and some dairy products, such as sour cream and yogurt can also interact with isoniazid. Avocados, bananas, and raisins, as well as many types of cheeses, such as mozzarella, American, and cheddar cheese should be restricted. All sources of caffeine, sauerkraut, and figs should also be consumed with extreme caution.


Consuming these foods while taking isoniazid may lead to an interaction. This can cause vomiting, nausea, and diarrhea. Chest pain, irregular heartbeat, and flushing may also occur. Some patients report a severe headache, flushing, and neck stiffness. Medical care must be sought immediately if a patient experiences these symptoms.

Patients should also be aware of other possible side effects from isoniazid. These can include eye pain and other vision problems, fever, and tenderness or pain in the stomach. Skin rash, swollen glands, sore throat and numbness or tingling in the extremities may occur. Those who experience these symptoms should contact a physician immediately.

Isoniazid may also interact with certain laboratory tests, such as urine glucose tests. Acetaminophen, antifungal medications, and phenytoin may also interact with isoniazid. Patients should discuss all their other medications and supplements with the prescribing physician prior to use.

There is insufficient evidence regarding the potential risk to an unborn or nursing baby while taking this drug, as of 2011. Patients should inform their doctor right away if they become pregnant. In addition, patients who have liver or kidney disease, diabetes, or human immunodeficiency virus (HIV) may need an adjusted dose of this drug.


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