Isoniazid is an approved antibiotic, which, in combination with other drugs, is the standard treatment for tuberculosis. In the United States, it is also commonly used as tuberculosis prophylaxis, although this is not common in the United Kingdom.

Isoniazid is also effective prophylaxis against tuberculosis in people with HIV, both in preventing infection and in preventing relapse after infection.1 2 Isoniazid preventive therapy is recommended by WHO for HIV-positive patients with exposure to TB confirmed by tuberculin skin test.3

Isoniazid comes as tablets, an elixir to be drunk or a liquid for intravenous injection. Its side-effects can include rash, fever, jaundice, peripheral neuropathy (nerve damage) and hepatitis. The risk of liver problems may be less than commonly believed: a literature search of published data and a survey sent to tuberculosis officers across the United States found that isoniazid was very safe especially when monitoring guidelines were followed, with no increase in the rate of fatal liver toxicity above that seen in the general population.4

Stomach upsets from isoniazid are reduced if it is taken with food. Supplements of vitamin B6 may help to reduce the risk of neuropathy and avoiding alcohol may help to minimise the chances of liver problems. Aluminium-containing antacids or laxatives should be avoided, as they reduce the amount of isoniazid that is absorbed from the gut.

Isoniazid does not interact with any currently available protease inhibitors or non-nucleoside reverse transcriptase inhibitors (NNRTIs).

Isoniazid is available as a generic (non-brandname) product. It is sometimes abbreviated to INH.


  1. Bucher HC et al. Isoniazid prophylaxis for tuberculosis in HIV infection: a meta-analysis of randomized controlled trials. AIDS 13: 501-507, 1999
  2. Fitzgerald DW et al. Effect of post-treatment isoniazid on prevention of recurrent tuberculosis in HIV-1-infected individuals: a randomised trial. Lancet 356: 1470-1474, 2000
  3. Grant AD et al. Effect of routine isoniazid preventive therapy on tuberculosis incidence among HIV-infected men in South Africa: a novel randomized incremental recruitment study. JAMA 293: 2719-2725, 2005
  4. Salpeter S et al. Isoniazid-related fatal hepatitis. West J Med 165: 323, 1996