Isoniazid (also called isonicotinyl hydrazine or INH; sold as Laniazid, Nydrazid)'s an organic compound that's the first-line antituberculosis medication in prevention and treatment. First discovered in 1912 as an inhibitor of the MAO enzyme, it was first used as an antidepressant, but discontinued due to side effects. In 1951, it was later discovered that isoniazid was effective against TB. Isoniazid's never used on its own to treat active tuberculosis because resistance quickly develops. The… (More on Isoniazid)