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Facts About...


Brand names

Isoniazid, Isotamine

Reason for taking this medicine

Isoniazid (INH) is used to treat or prevent tuberculosis (TB). It is used with other TB medicines.

How to take this medicine

  • It is very important that you take INH as prescribed
  • If you think you might be pregnant, or you are breastfeeding, tell your doctor/health care provider before starting INH
  • If you miss a dose, take it as soon as possible, but never take two doses at one time
  • It is best to take INH on an empty stomach (one hour before meal or two hours after)
  • If you get an upset stomach from INH, you can take it with foods that are low in fat and sugar
  • Antacids may help your stomach upset, but they must be taken one hour before or after INH
  • Do not drink alcohol when taking INH
  • Do not store INH in areas where there is direct sunlight, heat and/or moisture
  • Pyridoxine (vitamin B6) may be taken with INH to prevent numbness and/or tingling in your hands or feet
  • Your doctor/health care provider will order blood work to check your liver function regularly during your treatment


  • Tell your doctor/health care provider and pharmacist about any drug allergies before starting INH
  • Always tell your doctor/health care provider and pharmacist if you are taking other medicine or vitamins
  • Diabetic clients should know that INH may cause false test results with some urine sugar tests. Check with your doctor/health care provider
  • Avoid medicines that affect the liver (e.g., Tylenol)
  • Birth control pills may not work as well when taking INH. Use condoms or other birth control methods
  • Avoid foods containing tyramine (Swiss or Cheshire cheese, red wine), and fish (tuna, skipjack Sardinella). INH and foods with tyramine can cause flushing and/or itching of the skin with or without a rash, hot flashes, palpitations, headache, and/or increased blood pressure. This usually gets better within 2 hours

While most people can take INH with no problem, INH may cause some side effects. Tell your doctor/health care provider if you have:

  • Dizziness
  • Upset stomach
  • Feeling very tired
  • Clumsiness
  • Blurred eye sight (with or without pain)
  • Vomiting
  • Weight loss
  • Nausea
  • Skin rash
  • Numbness and/or tingling in hands or feet

INH can sometimes affect your liver. This is called hepatitis. Stop taking your TB medicines and call your doctor/health care provider right away if you have any of the following symptoms:

  • Yellowing of eyes and skin
  • Loss of appetite for a few days that is not going away
  • Severe nausea and vomiting
  • Stomach cramps or stomach pain
  • Fever, chills
  • Very dark urine
  • Feeling very tired or weak
August 2016