What is the most significant adverse effect of isoniazid (INH) used in tuberculosis treatment?

Isoniazid (INH) is well known for causing hepatotoxicity, which can range from asymptomatic transaminase elevation to fulminant hepatic failure. The risk increases with age, alcohol use, and concurrent use of other hepatotoxic drugs (including acetaminophen in high doses). Liver function tests should be monitored in patients on INH therapy. Other notable INH side effects include peripheral neuropathy (prevented by pyridoxine/vitamin B6 supplementation) and drug interactions via CYP450 inhibition. Ototoxicity and nephrotoxicity are associated with aminoglycosides (e.g., streptomycin), not INH.