Disease and Illness

Algoma Public Health

Isoniazid (INH)

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A patient’s guide to taking medicine for TB

What is INH?

Isoniazid (INH) is an antibiotic medicine used to treat tuberculosis (TB). There are two ways it is used:

1. To treat inactive (latent) TB
2. To cure TB disease (when taken with other medicines)

The TB germs are very strong and are hard to get rid of. You will need to take this medicine for 6 to 12 months in order to kill all the TB bacteria and cure TB disease. Your doctor will decide exactly how many months you will take the medicine.

How do I take this medicine?

  • It is very important that you take the medicine every day or as instructed by your doctor
  • Tell your doctor right away if you stop taking your medicine
  • If you miss a dose take it as soon as possible, but never take two doses at one time
  • Remember to tell your doctor about other medicines you are taking or any new medicines that you start taking
  • Try to take the medicine on an empty stomach. If it upsets your stomach, take it with food
  • Store INH in a cool, dry place
  • Birth Control pills may not work as well when taking INH. Use condoms or other birth control methods
  • Tyramine poisoning is rare, but may occur after ingesting foods or beverages with high monoamine content. If flushing occurs avoid these foods and drinks (e.g. Swiss cheese, beer, wine)
  • DO NOT drink alcohol while taking this medicine. You could damage your liver.


Why I might need to take Vitamin B6 (Pyridoxine) at the same time?

Vitamin B6 will help to prevent numbness and tingling in your fingers and toes that can be caused by INH. You may not need to take this vitamin if you are able to get enough as part of a healthy diet.

What are some side effects I should watch out for?


  • Most people have no problems while taking INH
  • You will need to be monitored regularly by your doctor while taking INH
  • Some common side effects are:
    - Skin rash
    - Loss of appetite

  • If you have any of the following more serious side effects, stop taking the medicine and call your doctor
    - Nausea / vomiting
    - Stomach cramps / pain
    - Fatigue / feeling very tired
    - Very dark urine
    - Painful or tingling feeling in fingers or toes
    - Yellowish skin or eyes
    - Fever for three days or more

Tips for taking your TB medicine

  • Take your medicine at the same time every day, for example
    - Before going to bed
    - First thing in the morning
  • Use a weekly pill container
  • Mark off each day you take your pills on a calendar
  • Ask a family member or friend to remind you
  • Consider Directly Observed Therapy (DOT)


If you have any questions about your medicines or TB, please contact your doctor or Algoma Public Health at 705-942-4646.