Isoniazid is also called isonicotinyl hydrazine or INH. Isoniazid is a first-line antituberculous medication used in the prevention and treatment of tuberculosis. Isoniazid is never used on its own to treat active tuberculosis because resistance quickly develops.

Isoniazid has no use except in the treatment of mycobacterial infection. It was discovered in 1952, when for the first time, a cure for tuberculosis was considered reasonable. It is available in tablet, syrup, and injectable forms (given intramuscularly or intravenously). Isoniazid is available world-wide, is inexpensive to produce and is generally well tolerated.