Isoniazid is a bactericidal agent active against organisms of the genus Mycobacterium, specifically M. tuberculosis, M. bovis and M. kansasii. Isoniazid is recommended for all forms of tuberculosis in which organisms are susceptible. Isoniazid is a prodrug and must be activated by bacterial catalase. Isoniazid inhibits InhA, the enoyl reductase from Mycobacterium tuberculosis, by forming a covalent adduct with the NAD cofactor. The most frequent adverse reactions to isoniazid are those affecting the nervous system and the liver.

Isonicotinamide is the amide form of isonicotinic acid. It is often used as a scaffold for other synthetic compounds. Isonicotinamide has been identified as inducing apoptosis through DNA fragmentation in leukemia cell models and has been studied in mice or the prevention of diabetes. Isonicotinamide activates the NAD-dependent histone deacetylase SIR2 by raising intracellular NAD+ concentration.