Isoniazid is used for all forms of tuberculosis. It can be used on its own for latent TB, or in combination with other drugs for active TB.

Why have I been prescribed Isoniazid?

  • Isoniazid is recommended for all forms of tuberculosis.
  • It can be used on its own for latent TB, or in combination with other drugs for active TB.

How does it work?

Isoniazid stops the growth of the bacteria that causes TB.

When and how do I take it?

Do NOT take with food. Take with a glass of water and at intervals indicated by your doctor.

What’s the dose?

Usual Oral Dosage (depending on the regimen used):


  • 5 mg/kg up to 300 mg daily in a single dose; or
  • 15 mg/kg up to 900 mg day, two or three times/week


  • 10-15 mg/kg up to 300 mg daily in a single dose; or
  • 20-40 mg/kg up to 900 mg/day, two or three time/week

Could it interact with other tablets?

Tell your doctor or pharmacist if you are taking any of the following:

  • Paracetamol
  • Carbamazepine for seizures/epilepsy/neuropathic pain
  • Sodium Valproate for epilepsy
  • Ketoconazole for fungal infections
  • Phenytoin for epilepsy
  • Theophylline for asthma and respiratory conditions.

Herbal products should also only be taken after talking with your doctor.

What are the possible risks or side-effects?

The most frequent reactions are those affecting the nervous system and the liver.

Nervous System Reactions:

  • Peripheral neuropathy (Nerve Damage) is the most common toxic effect. It is dose-related, occurs most often in the malnourished and in those predisposed to neuritis (e.g. alcoholics and diabetics), and is usually preceded by pins and needles type symptoms of the feet and hands.
  • Other neurotoxic effects, which are uncommon with conventional doses, are convulsions, toxic encephalopathy, optic neuritis and atrophy, memory impairment, and toxic psychosis.

Liver Reactions:

  • Abnormal liver function tests and levels, jaundice, and occasionally severe and sometimes fatal hepatitis. The common symptoms of hepatitis are weight loss, nausea, vomiting, fatigue, malaise, and weakness.This abnormality usually appears in the first 1 to 3 months of treatment but can occur at any time during therapy.
  • The frequency of progressive liver damage increases with age. It is rare in persons under 20, but occurs in up to 2.3 percent of those over 50 years of age. It is more likely in patients with a daily alcohol intake.

Gastrointestinal Reactions:

  • Nausea
  • vomiting
  • epigastric distress

Can I drink alcohol while taking it?

Alcohol should be avoided while taking Isoniazid.

What if I’m pregnant/breastfeeding?

Tell your doctor if you are pregnant as he/she will have to weigh the benefits aginst the risks of treating you with isoniazid while pregnant.

It is OK to take Isoniazid while breast feeding, but again, let your doctor know first.

If you have any more questions please ask your Pharmacist.

Remember to keep all medicines out of reach of children
Please Note:
We have made every effort to ensure that the content of this information sheet is correct at time of publish, but remember that information about drugs may change. This sheet does not list all the uses and side-effects associated with this drug. For full details please see the drug information leaflet which comes with your medicine. Your doctor will assess your medical circumstances and draw your attention to any information or side-effects which may be relevant in your particular case.



Health Reference: Tuberculosis