Isoniazid Fact Sheet
Medication Information
Isoniazid is an antibiotic medication used to treat Tuberculosis (TB) disease along with other medications. Isoniazid is also used to treat Tuberculosis Infection (TBI).
The TB germs (bacteria) are very strong and are hard to get rid of. You will need to take this medication for six to 12 months to kill the TB bacteria. Your health care provider will decide how many months you will need to take the medication.
Taking the Medication
- It is important to take this medication every day at the same time, for example, always before going to bed or always first thing in the morning.
- This medication works best on an empty stomach (one hour before or two hours after a meal). However, if it upsets your stomach, you may take it with food.
- Take all the medication that you are prescribed.
- Even if you start to feel better, it is important to keep taking this medication until the healthcare provider tells you to stop. Contact your healthcare provider immediately if you stop taking your medication.
- See your healthcare provider on a regular basis while you are taking this medication and follow instructions regarding blood work.
- Your doctor may ask you to also take vitamin B6 (Pyridoxine). Vitamin B6 helps prevent numbness and tingling in your fingers and toes which may be caused by Isoniazid.
Possible Side Effects
Contact your healthcare provider immediately if you experience any of the following side effects:
- Painful or tingling feeling in fingers or toes
- Skin rash
- Loss of appetite
- Nausea, vomiting
- Stomach cramps and pain
- Dark urine
- Yellowing of the skin or eyes
- Unexplained fatigue, tiredness, weakness
Other possible side effects include:
- Heartburn
- Diarrhea (can occur with liquid medication)
- Feeling week, or unwell
- Fever
- Difficulty with speech, inability to concentrate or altered mood
- Headache
- Mild hair loss
- Flushing (if flushing occurs avoid aged cheeses, cured meats, fermented cabbage (e.g. sauerkraut), soya sauce, fish or shrimp sauce, yeast-extract spreads (e.g., marmite), broad bean pods (e.g., fava beans).
If you are concerned about these or any other side effects, call your healthcare provider.
Precautions
- Do not drink alcohol. Drinking alcohol can increase the chance of liver problems while you are taking Isoniazid.
- Talk to your healthcare provider about other medications you are taking or any new medications that you start taking including any drugs, vitamins, minerals, natural supplements, or alternative medicines.
- Follow your healthcare provider’s advice about taking this medication if you are pregnant or breastfeeding.
- Do not share your medication with anyone.
Drug Interactions
- If you take antacids (e.g., Tums®, Rolaids®), take Isoniazid at least one hour before or two hours after taking an antacid.
Missed Doses
- If you miss a dose, take it as soon as possible. If it is almost time to take your next dose, do not take the missed dose. Do not take two doses at the same time.
Storage
- Store the medication at room temperature in a cool dry place. Do not put in in the refrigerator. Keep our of reach and sight of children.
A public health nurse will contact you on a regular basis while taking Isoniazid.
For further information, please contact the Communicable Disease Control Program at 705-474-1400 or toll free at 1-800-563-2808, ext. 5229 or email us at cdc@healthunit.ca.
References
- Pendopharm, Division de/of Pharmascience Inc. (2020). Prescribing Information pdp-Isoniazid Isoniazid Tablets USP 50mg, 100mg, 300mg, Isoniazid Oral Solution USP 50mg/5mL. Retrieved from: https://pdf.hres.ca/dpd_pm/00059225.PDF.
- James C. Johnston, Ryan Cooper & Dick Menzies (2022) Chapter 5: Treatment of tuberculosis disease, Canadian Journal of Respiratory, Critical Care, and Sleep Medicine, 6:sup1, 66-76, DOI: https://www.tandfonline.com/doi/full/10.1080/24745332.2022.2036504
Created: Sep 2026, by CDC